Study Unit - Automotive Cooling Systems

8/13/2019 Study Unit - Automotive Cooling Systems

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Study Unit

AutomotiveCooling Systems


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In this study unit, youll learn why proper temperature control is important to engine operation.As an engine operates, combustion produces a lot of heat. This heat must be removed to preventthe engine components from being damaged. At the same time, however, the engines temperature

must be kept high enough to ensure efficient operation. In an automotive engine, the cooling sys-tem is designed to maintain the proper operating temperature within an engine at all times.

In this study unit, youll learn how each of the individual cooling-system components works, andhow all the components work together to deliver coolant to all parts of an engine. Youll learnabout the different types of coolant, and how they help protect engines from heat damage as well

as from rust and corrosion. Finally, youll learn how to perform routine maintenance procedureson the cooling system, and how to troubleshoot problems within the system.

When you complete this study unit, youll be able to

Map the flow of coolant through an automotive cooling system

Explain the function of each cooling-system component

Describe the steps you would take to inspect, test, and repair an engines cooling system

List the common reasons why an engine overheats

Describe how to measure the pressure in a cooling system

Name the locations where coolant leaks are likely to occur in an automotive cooling system

Describe how to replace the different components in the cooling system

Analyze a description of a problem within an engine and determine the problem within thecooling system

Preview

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SUMMARY 97

POWER CHECK ANSWERS 99

E X A M I N A T I O N 1 0 1

vi Contents


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AUTOMOTIVE COOLING SYSTEMS

Introduction

As youve learned, an automotive engine produces a great deal of heatas it operates. This heat is produced by the burning air-and-fuel mix-ture inside the engines cylinders. Its normal for an engine to become

hot during operation; however, excessive heat can damage an engine.Too much heat in an engine can actually cause components to melt. Ifthe engine becomes too hot, the valve heads and the piston heads usu-ally experience the most damage, since these components are locatedin the combustion chamber, where temperatures are the highest. Highengine temperatures can also cause fuel to evaporate before it reachesthe combustion chamber, thus preventing the engine from running.

At this point, you may think that a cold engine runs better than a hotone. Well, this isnt really true. An engine thats too cold produces lesspower and is less efficient than a warm engine. In a cold engine, the in-take manifold is cold. As the fuel vapor comes in contact with the coldmanifold, the fuel condenses and forms droplets on the manifold walls.

This condensation causes a reduction in engine power, since vaporizedfuel burns better than liquid fuel. More fuel needs to be supplied to acold engine to compensate for condensation. This means a cold engineuses more fuel to produce the same amount of power as a warm engine.You may have noticed this when operating your own vehicle. Mostautomotive engines operate better after theyve run for a few minutes.

As you can see, an engine thats either too hot or too cold wont runproperly. Because an engines temperature is so important to its opera-

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Before you learn about cooling systems in detail, lets take a look atsome of the ways heat is removed from an engine.

Three Methods of Heat Removal

There are three different methods used to remove heat from an object,including an engine: conduction, convection, and radiation. Lets take

a look at these three heat removal methods in detail.

Conductionis the direct transfer of heat from one object to another.Burning your finger on a hot stovetop is one example of conduc-tionthe heat from the stovetop is transferred to your finger. Heatmay be transferred by conduction between any two solid ob-

jectssuch as the stove and your fingerbetween a solid object and a

liquid, or between two liquids. For example, if you place a hot metalobject into a bucket of cool water, the objects heat is transferred intothe water that surrounds it. As a result, the object is cooled.

Conduction is used to cool automotive engines. In most engines, a liq-uid coolant is circulated through the engine components to keep them

cool. As the liquid flows through the engine, it picks up heat from thehot metal parts that it touches. The heat from the engine is then con-ducted into the liquid.

Convectionis the transfer of heat from an object to the air that sur-rounds it. If you take a hot dish of food out of an oven and allow it tocool on your countertop, you have cooled the food by convection. Theheat of the food is absorbed into the cool air that surrounds it. Cooling

by convection would also occur if you placed the hot dish of food in-side a refrigerator. Even though the food isnt in direct contact with therefrigeration unit, its cooled by the cold air that surrounds it.

Some of the heat in an automotive engine is removed by convection.

Under the vehicles hood, cool outside air surrounds the engine. Someof the engines heat is absorbed by this air as it passes over the engine.

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The third possible method of heat removal isradiation. Radiation is thetransfer of heat through energy waves that are similar to light waves.

In this heat removal method, some of the heat energy from one objectis transferred through the air to another nearby object. The heat pro-duced by the sun is radiant energy. The suns heat is actually waves ofheat energy that move from the surface of the sun to the earth. We canall feel the suns heat from a great distance, so you can see how power-ful radiant heat can be.

An automotive engine loses some heat through radiation. A smallamount of heat produced by the engine radiates to and is absorbed byother nearby automotive parts, such as the frame and body panels. Ifyou place your hand on a cars hood after the engine has been runningfor a while, you can feel this radiant heat.

In order to remove as much heat as possible, a typical automotive en-gine uses a combination of all three heat removal methods to maintaina proper operating temperature. Radiation and convection removesome heat, but the vast majority of an engines heat is removed by con-duction. In a typical liquid-cooling system, heat is transferred from thehot engine parts to a liquid coolant through conduction. Then, the

warm liquid coolant is removed from the engine and circulatedthrough a radiator, where more heat is removed through convectionand radiation.

Now, lets look at the basic operation of an automotive cooling system.

Liquid-Cooling Systems

As you just learned, an automobile can contain either a liquid-coolingsystem or an air-cooling system. Liquid-cooling systems are the mostcommon. An engine that uses a liquid-cooling system is simply calledaliquid-cooled engine. In this type of system, a liquid coolant is pumped

through passages in the engine. The coolant absorbs heat from the hotmetal components as it flows through the engine passages. The liquid

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self. A typical engine block isnt a solid piece of metal. Instead, the en-gine block is somewhat hollow, especially in the area around each

cylinder. These hollow areas in the engine block are called the waterjackets, because they surround the cylinders just as a jacket would sur-round the person wearing it.

As the engine operates, coolant flows through the water jackets. Sincethe hottest areas of the engine block are the areas that surround eachcylinder, the coolant that flows through these areas removes most ofthe heat thats produced during combustion. So, as the air-and-fuelmixture is burned in the cylinders, the heat of combustion is trans-ferred to the liquid coolant that circulates around the outside of thecylinder walls. In most engines, the water jackets are relatively large,and allow a large volume of liquid coolant to flow through the engine.In general, the larger the water jackets, the easier it is to keep the en-

gine cool.

In addition to circulating in the water jackets, coolant also circulatesthrough the inside of the cylinder head. Like the engine block, the cyl-inder head also contains coolant passageways, particularly around thecombustion chambers. Coolant flows to the cylinder head through pas-

sageways that lead from the water jacket in the engine block.In order to properly remove heat from an engine, coolant must be con-tinually circulated through the cooling system. The component thatcirculates the coolant through an engine is thewater pump. The waterpump is usually mounted near the front of the engine, often right intothe engines front cover. The design of water pumps varies from en-

gine to engine, but they all work in a similar way. On most engines,the water pump is driven by the crankshaft. Usually, a pulley on thefront end of the crankshaft is connected to a pulley on the water pump

by a rubber fan belt(Figure 1A). The belt causes the water pump shaftto rotate as the crankshaft turns. As the water pump shaft rotates, cool-ant is pumped through the water jacket and the other water passages.

Running the water pump off the crankshaft ensures that the waterpump operates whenever the engine is running.


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A radiator contains many small tubes that coolant can flow through.Each of these tubes is surrounded by thin metal plates called fins. The

fins increase the amount of surface area on the radiator thats exposedto the air, allowing the radiator to cool better. As air flows through theradiator, it cools the coolant that flows inside the small tubes in theradiator.

Once the coolant has been cooled by the radiator, the coolant is circu-lated back into the engine by the water pump. The radiator is con-nected to the engine and to the water pump by rubber hoses calledradiator hoses. Most cooling systems contain two separate radiatorhoses: anupper radiator hoseand alower radiator hose(Figure 1B).Theupper radiator hose carries the coolant from the engine to the radiator.This hose is called the upper hose because its usually attached to thetop of both the engine and the radiator. The lower hose, also called the

inlet hose,carries coolant from the radiator back to the engine. Thishose is called the lower hose because its usually mounted on thelower part of the radiator and engine.

As you can see, the coolant in the radiator is cooled by the air thatblows through it. Therefore, the radiator is usually mounted at the

very front of the vehicle so air can blow through it. This positioning al-lows air to be directed into the radiator as the vehicle moves down theroad.

This system works well when a vehicle is moving, but what happenswhen a vehicle is standing still? When a vehicle is standing still, no airflows naturally through the radiator, so a fan is needed to keep the ra-

diator cool. The fan also helps to increase the flow of air through theradiator when a vehicle is moving. This is especially useful in very hotweather, when the radiator may need some additional air cooling.

In many automotive engines, the fan is mounted to the water pump.This allows the fan to be driven by the same rubber belt that drives the

water pump. This type of fan is called abelt-driven fan. However, insome engines, the fan may be operated by a small electric motor. This




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creases even more. Thus, if water is mixed with antifreeze and is thenplaced under pressure, it boils at a much hotter temperature than 212

degrees. Therefore, both methods are used to prevent the coolant in anautomotive cooling system from boiling.

Because pressurizing the coolant raises its boiling point, most automo-tive liquid-cooling systems are pressurized systems. This means thatthe coolant in the system is under pressure while the engine is operat-ing. This pressure in the system develops because as the coolantwarms, it expands. The amount of pressure in the system is controlled

by a special cap on the system called apressure cap. The pressure capprevents coolant from escaping out of the system as long as the pres-sure stays below a specified safe level, usually about 1015 psi. If thepressure in the system gets higher than that, the pressure cap opensand releases some coolant until the pressure once again falls below the

specified safe level. The coolant thats let out by the pressure cap flowsthrough a small rubber hose to a plastic holding bottle called a coolantrecovery tank. When the engine cools down, a valve in the pressure capopens to allow the coolant to reenter the cooling system.

Now, lets look at how the temperature in the cooling system is con-

trolled. The device that controls the cooling-system temperature iscalled athermostat. The thermostat is a check valve that controls whenthe coolant is allowed to leave the engine and pass through the radia-tor. When an engine is cold, the thermostat stays closed and blocks theflow of coolant out of the engine. The thermostat wont open until theengine reaches its proper operating temperature, which is usually be-tween 180 and 210 degrees Fahrenheit. When the engine reaches its op-

erating temperature, the thermostat opens and allows coolant to flowout of the engine and into the radiator to be cooled. Remember that anengine wont run efficiently if its too cold. If the coolant was allowedto flow through the engine before it was warm, the engine would becooled too much and would never reach its correct operating tempera-ture. This is why the thermostat wont open until the engine reaches its

proper operating temperature.




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Youll examine the operation of the heater system in much more detail

in a later study unit. However, keep in mind that some coolant is di-rected to a vehicles heating system.

Coolant may also be routed to other engine components. For example,a small amount of coolant may be used to cool a turbocharger unit(Figure 3),or to help cool the oil in an engines lubrication system.

Engine Coolant


FIGURE 2The compo-nents of a typicalheater system are

shown here.

FIGURE 3On manyturbocharged engines,a small amount ofcoolant from the cool-ing system is routedthrough the turbo-charger to prevent oilbreakdown or bearing

failure.


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the coolant, as well as lower its freezing point. Because of this, the en-gine temperature can rise well above its normal operating temperature

without causing the coolant to boil and turn to vapor.

Most antifreeze contains additives that prevent rust and corrosion inthe cooling system. In addition, many types also contain special lubri-cants that lubricate moving parts, such as the water pump. As you cansee, antifreeze greatly enhances the protective abilities of the coolant inan engine.

Types of Antifreeze

Up until a few years ago, all automotive antifreeze was made from thesame ingredients. However, in recent years, some new materials have

been added to the old antifreeze formula. The following three types of

antifreeze are commonly used today: (1) ethylene glycol antifreeze; (2)extended-life antifreeze; and (3) low-tox antifreeze.

Automotive antifreeze is produced by several different manufacturers;however, its all similar. The purpose of the antifreeze is the same, re-gardless of its type. All antifreeze is mixed in the same way, using thesame mixture ratios. A vehicles service manual usually lists the manu-facturers recommended antifreeze; however, in most cases, any typeof antifreeze can be used in any vehicle. Lets take a closer look at eachtype of antifreeze.

Ethylene Glycol Antifreeze

In the past, the most common type of antifreeze used in automobileswas made of a compound called ethylene glycol. This compound ismixed with plain water to form the coolant mixture thats used in anengine. Adding ethylene glycol antifreeze to the water in a cooling sys-tem raises the boiling point and lowers the freezing point of the cool-ant. In addition, special additives in the ethylene glycol antifreeze help

prevent corrosion in the system, and also provide some lubrication forthe water pump.

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Extended-Life Antifreeze

Because the life of traditional ethylene glycol is limited, some manufac-turers now produce an extended-life antifreeze that lasts much longerthan ordinary antifreeze. Extended-life antifreeze is a special type ofantifreeze that contains anticorrosion additives. These additives extendthe life of the antifreeze and allow it to be used much longer before ithas to be replaced. One type of extended-life antifreeze is calledDex-

Cool,and is produced by Havoline.Extended-life antifreeze is still based on ethylene glycol; however, un-like ethylene glycol antifreeze, extended-life antifreeze doesn't need to

be changed every year. Instead, extended-life antifreeze may need tobe changed only after every 100,000 miles, or every five years.Extended-life antifreeze lasts approximately five times as long as tradi-

tional antifreeze. Because it provides better protection and doesntneed to be changed as often, extended-life antifreeze is becoming verypopular.

Because ethylene glycol antifreeze and extended-life antifreeze containdifferent ingredients, the two types of antifreeze shouldnt be mixedtogether. Extended-life antifreeze is usually brownish-orange in color,

so it can be easily distinguished from traditional ethylene glycol anti-freeze, which is usually pale green.

Low-Tox Antifreeze

Youve learned that both ethylene glycol antifreeze and extended-life

antifreeze are commonly used in automobiles, and provide good pro-tection. However, antifreeze thats made from ethylene glycol is poi-sonous if ingested. If ethylene glycol antifreeze is ingested, it can causecrystals to form in the kidneys, which can cause permanent kidneydamage or even death. This makes these substances hazardous tosmall children and pets. Ethylene glycol antifreeze has a sweet taste

and smell thats very appealing to pets, and its bright color may attractsmall children. For this reason, its important to keep the antifreeze out

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Now, take a few moments to review what youve learned by complet-ingPower Check 1.

Power Check 1

At the end of each section ofAutomotive Cooling Systems,youll be asked to pause andcheck your understanding of what youve just read by completing a Power Check ex-ercise. Writing the answers to these questions will help you to review what youve stud-ied so far. Please completePower Check 1now.

1. Antifreeze made from propylene glycol is called _______ antifreeze.

2. A combination of three heat removal methods is used to remove the heat fromautomotive engines. These three methods are _______, _______, and _______.

3. A mixture thats one-half water and one-half antifreeze is called a _______.

4. The transfer of heat from an object to the air that surrounds it is called _______.

5. The coolant liquid thats used in a liquid-cooling system is usually a mixture of waterand _______.

6. The transfer of heat through energy waves is called _______.

7. In a liquid-cooled engine, the hollow areas around the cylinders that hold coolant arecalled _______.

8. The direct transfer of heat from one object to another is called _______.

Questions 920: Indicate whether the following statements are True or False.

_____ 9. A warm engine uses more fuel to produce the same amount of power as a coldengine



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COOLING-SYSTEM COMPONENTS AND THE FLOW OFCOOLANT

The Water Pump

Power Check 1

_____ 14. If you place pressure on liquid coolant, the boiling point of the coolant increases.

_____ 15. When antifreeze is added to plain water, the resulting mixture has a lower freez-ing point than plain water.

_____ 16. Most antifreeze contains additives that help prevent rust and corrosion, as wellas lubricants that help lubricate moving parts.

_____ 17. As a rule, regular ethylene glycol antifreeze should be drained from a vehicleand replaced at least once a year.

_____ 18. Extended-life antifreeze lasts approximately ten times longer than regularantifreeze.

_____ 19. Regular ethylene glycol antifreeze and extended-life antifreeze can be mixed

together and used in a cooling system.

_____ 20. Antifreeze made from ethylene glycol can be poisonous if ingested.

Check your answers with those on page 99.



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The construction of a water pump is relatively simple. Three views of atypical water pump assembly are shown inFigure 5. The main parts of

the pump are the cast-ironor aluminumpump housing, a steel shaft,and metal impeller blades(Figure 5A).The housing has two openings,acoolant inletand acoolant outlet. The impeller blades are attached tothe end of the rotating shaft, and the shaft and impeller assembly isheld inside the housing. Bearings are used to support the shaft and al-low it to spin freely. A pump also has a seal that holds coolant insidethe pump and prevents it from leaking out around the rotating shaft(Figure 5B).The impeller blades are designed to circulate waterthrough the cooling system. A gasket fits between the pump and blockto keep the assembly from leaking(Figure 5C).

Figure 6shows an external view of a typical water pump installation.This pump is bolted to the front of the engine block. A rubber drive

belt connects a pulley on the end of the water pump shaft to a pulleyon the end of the crankshaft. Once the engine is started, the belt trans-fers the rotation of the crankshaft to the water pump shaft, causing theshaft to rotate. As the water pump shaft rotates, the impeller bladesalso rotate, moving the coolant around in the cooling system. In mostvehicles, the water pump is mounted to the engines front cover in this

way and driven by the crankshaft. Running the water pump off thecrankshaft ensures that the pump operates whenever the crankshaft isturningthat is, whenever the engine is turned on.

InFigure 6,a fan is attached to the end of the water pump shaft. Thisfan is used to draw cool air through the radiator. In this system, the fanis driven by the same belt that drives the water pump.

Note the connection of the upper radiator hose and the lower radiatorhose to the water pump. Also, note that this water pump also has a by-pass hose attached to it. The bypass hose allows coolant to circulatefrom the engine block back into the pump when the thermostat isclosed. This type of bypass arrangement is used on many cars.

Now, lets take a closer look at the internal operation of a water pump. A



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FIGURE 6This figure shows an external view of a typical water pump installation. Note the connections ofthe hoses and the fan in the illustration.



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The Water Pump Drive Belt

In most engines, the water pump is driven by a rubber belt that connectsthat pump to the crankshaft. Once the belt is in place, the belt causes thewater pump shaft to operate whenever the crankshaft rotates.

Two common types of belts are used on automobiles: theV-type beltand theserpentine belt. The V-type belt gets its name from its cross-

section, which looks like the letterV. Several V-type belts may be usedin an engine to drive its accessories, such as the water pump.

A typical V-type drive belt is shown inFigure 8A,andFigure 8Bshows a cross-section of the belt construction. Note how the belt is aclosed loop. Most V-type belts are made of rubber with strands of fibermolded into the rubber to give the belt strength. V-type belts come in

different lengths and different thicknesses. Each make and model ofvehicle uses a different belt. For this reason, a belt must be replacedwith a belt thats specifically made for that vehicle.

The inner sides of the V-belt fit in the pulleys that are used to drive thebelt. Each pulley has a V-shaped groove in it to match the shape of the

belt. Once the belt is installed in the pulley groove, the sides of the beltare in contact with the inner sides of the pulley. Because a large area of

FIGURE 8A typical V-typedrive belt is shown in Figure8A, and Figure 8B shows a

cross-section of the beltconstruction.



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Figure 10Ashows an engine that uses a serpentine belt to drive all of

its accessories.Figure 10Bshows a more complex serpentine drive beltsystem that drives more accessories, including the water pump, thepower-steering pulley, the alternator, and the air-conditioning com-pressor.

In each of these figures, you can also see the idler pulley that the ser-

pentine belt wraps around. This idler pulley is used to keep the propertension on the belt at all times. The idler pulley is made so that it canmove side to side. A larger spring is built into the idler pulley thatkeeps the pulley pushing on the belt to keep the tension tight. The en-gines service manual contains a diagram of the proper routing of theserpentine belt.

The Coolant Passages

As you learned, coolant flows thorough passages in the engine blockand the cylinder head to help to keep the engine cool. As the coolantflows through these passages, it absorbs heat from the parts and trans-

fers it outside the engine to the radiator, where the heat can be re-leased. Coolant passages are machined into an engine block orcylinder head when theyre manufactured. The largest passages arefound near the cylinders, especially around the combustion chambers,where most of an engines heat is produced.

When coolant passages are machined into an engine block, openingsare often left in the block from the machining process, mainly around

FIGURE 9A cross-section of a typical ser-pentine belt is shown

here. (Courtesy of ChryslerCorporation)



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block. Core plugs are made of thin metal and are made to be slightlylarger than the openings in the engine block. The plugs are pressed

into the side of the engine block to form a tight seal. Usually, the plugsare installed by tapping them into place with a hammer and punch.Since the plugs are a little larger than the holes in the block, the plugsfit tightly, and they prevent any coolant from leaking out of the engine

block. In addition, since the plugs fit so tightly in the block, the plugswont come out, even with the pressure of the coolant in the system.

An engine block usually also contains a hole that leads into the waterjacket. This hole is usually much smaller than the other holes, and issealed off with a small threaded plug called ablock drain plug(Figure 12).An automotive technician uses this threaded plug to drainthe coolant from the block during servicing. The plug can be un-threaded from the block and removed, which allows the coolant to

drain from the block. Since the block drain plug is used to drain thecoolant out of the block, its usually located on the side of the engine

block, near the bottom of the water jacket. An in-line engine usuallycontains one block drain plug. However, a V-type engine that has twoseparate rows of cylinders usually contains two block drain plugs, oneon each side of the engine.

FIGURE 11This figureshows core plugs in-stalled in an engineblock.

FIGURE 12A hole inthe engine block thatleads into the waterjacket is sealed off witha small threaded plugcalled a block drain

plug. The block drainplug is removed from



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The Radiator

As youve learned, a radiator is a type of heat exchanger thats used toremove heat from the coolant that has circulated through a hot engine.A radiator usually has three main components: a core and two tanks.The core is the center section of the radiator where the cooling takesplace. The tanks on each end of the radiator direct the flow of coolantin and out of the radiator core. An external view of the components of

a typical radiator is shown inFigure 13.

FIGURE 13An external view of the components of a typical radiator is shown here.



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Small holding tanks made of brass or plastic are mounted directly toeach end of the radiator core. The holding tanks hold the coolant as itflows in and out of the core. The radiator tanks are usually solderedonto the radiator core if the tank is made of brass, or glued onto thecore if the tanks are plastic. (The glue thats used for this purpose issimilar to the glue used in a hot glue gun for hobbies and crafts.) Eachtank has an opening that allows the coolant to flow in or out. In a typi-cal cooling system, the coolant flows into the tank through a radiatorhose thats attached to the tank opening. The coolant then flows fromthis tank into the small tubes of the radiator core, and then out to thetank on the other side of the radiator. The coolant then flows out of thetank through another radiator hose, and back into the engine.

In addition to the openings where the radiator hoses attach, one radia-tor tank usually has an additional opening called thefiller neck. Thefiller neck holds the radiators pressure cap and is usually located atthe very top of the tank. This allows the cap to be removed easily sothat the cooling system can be filled with coolant.

An additional opening in the radiator tank is usually located on the

FIGURE 14A cutaway view of a typical radiator core is shown here.



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through a tube thats placed inside one of the radiator tanks. The tubeis sealed so that the transmission fluid cant mix with the coolant. One

line transfers fluid from the transmission to the radiator, and the otherline returns the fluid back to the transmission. As the transmissionfluid flows through the tube in the radiator tank, the heat is removed

by the coolant flowing around the outside of the tube. Youll learnmore about the operation of the transmission cooler in a later studyunit. For now, just keep in mind that many radiators perform thisfunction.

FIGURE 16Metal lines at-tached to the radiator tanks

connect a vehicles radiatorto its transmission.

FIGURE 15Figure 15Ashows the location of thepetcock on the radiator,and Figure 15B shows aclose-up view of the pet-cock after it has been re-

moved from the radiator.



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The flow of coolant through a cross-flow radiator system is shown inFigure 18A.In a cross-flow radiator, the radiator tanks are mounted oneach side of the radiator core, and the small tubes in the core run fromside to side. The coolant enters the radiator through one of the side

tanks, then flows across the radiator core to the tank on the other side.This type of radiator is used in most modern cars. Because the radiatortanks are mounted to each side, the overall height of the radiator iskept low. This allows the radiator to fit easily in smaller vehicles wherespace is somewhat limited.

Top-flow radiators are mainly seen in older cars and larger trucks. In a

top-flow radiator, the radiator tanks are mounted to the very top andb f h di Th ll b h h l

FIGURE 17A cross-flow radiator is shown in Figure 17A, and a top-flow radiator is shown in Figure 17B.



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from flying into its opening. If foreign objects or debris were to enterthe opening, they could damage the radiator core. In other vehicles, airis directed into the radiator from below the front of the car. A specialair deflector called afront air damor aspoilercatches the air and directsit up into the radiator core.



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No matter how air is brought into the radiator, once it gets there, theair flows through the core, removing heat from the coolant along theway. The air then leaves the radiator core, flows through the areawhere the engine is mounted, and then flows back outside the vehicle.

All radiators operate similarly. However, the height, width, and corethickness of a radiator depend on the model of the car. Different radia-tors may also use different mounting brackets and hose connections. Be-cause of these differences, the radiator from one vehicle cant usually be

used in another vehicle. If a radiator needs to be replaced, it must be re -placed with a radiator thats designed especially for that vehicle model.

The Radiator Pressure Cap

As you learned earlier in this study unit, one of the tanks on a radiator

has a filler neck where coolant can be added. This is the also where theradiators pressure cap is attached. Theradiator pressure capis used tocontrol the amount of pressure thats generated in the cooling system.The cap prevents coolant from escaping out of the radiator as long asthe pressure stays below a specified safe level.

When an engine is cold, theres no pressure in the cooling system.

However, when the engine is started and begins to warm up, the cool-ant in the system expands. Since an automotive cooling system is aclosed system, the expansion of the coolant causes the pressure in thesystem to rise. This increase in pressure isnt a problem. In fact, it actu-ally benefits the system. The higher the pressure in the system, thehigher the boiling temperature of the coolant. This means that the en-

gine can operate at a higher temperature without the coolant boilingand turning to a vapor.

Although the pressure in the cooling system is useful, too much candamage the system. If the pressure becomes excessive, the cooling sys-tem components may not be able to withstand the pressure. Usually,levels between 16 and 20 psi are considered excessive.

Thus, a cooling system must have a way to control this pressure. The



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drops below the caps rating, the valve closes and seals the systemagain.

InFigure 19,note the large round disk and rubber gasket at the bottomof the cap. Together, this disk and gasket are called the blow-off valve.The blow-off valve seals against the filler neck and prevents coolantfrom leaking out of the radiator. The metal disk is held in place by aheavy spring. The strength of this spring determines the caps rating.The stronger the spring, the more pressure is required to overcome the

spring pressure and move the metal disk up off the filler neck. A cuta-way view of the components of a radiator pressure cap can be seen inFigure 20.

FIGURE 19The radiatorcap is mounted to the ra-diator tank as shown here.



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As an engine heats up, the coolant begins to expand and push directlyagainst the metal disk and gasket on the cap. Once the pressure in thesystem becomes excessive, the coolant pushes hard enough on the capto overcome the spring and push the disk up off the filler neck. Oncethe disk is pushed up, coolant can leak around the outside of the diskand out of the radiator. In most vehicles, the coolant thats allowed tooverflow the radiator enters a tube called anoverflow tube,as shown inFigure 21A.The overflow tube leads to a storage tank called the cool-ant recovery tank.

As some of the coolant leaves the system, the pressure inside the cool-ing system drops. Once the pressure drops below the rating of the cap,the spring in the cap forces the disk and gasket back down against thefiller neck, thus sealing the cooling system once again. When the en-gine cools down and the coolant pressure is reduced, a vacuum pres-

sure is produced in the system. This vacuum pressure causes the smallvacuum valvein the center of thedisk to open, allowing some coolant toreturn to the system as shown inFigure 21B.

FIGURE 21The operation of a radiator pressure cap is shown here. In Figure 21A, rising pressure in the cool-ing system causes the blow-off valve to open and release coolant into the overflow tube. In Figure 21B, thepressure in the system has lowered, and the vacuum pressure created in the system causes the vacuumvalve to open. When the vacuum valve opens, some coolant returns to the system through the overflow



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Although this method was used for many years, it had several disad-vantages. First, the coolant draining onto the ground was bad for theenvironment. Second, each time the pressure cap valve opened, cool-ant would be permanently lost, so the system would require frequentrefilling.

To solve these problems, the coolant recovery system was developed.The coolant recovery system catches excess coolant that leaves thecooling system, and then returns it to the system after the engine has

cooled and the pressure has lowered. A coolant recovery system canbe found in almost every vehicle produced today.

The coolant recovery system contains two basic parts: the vacuumvalve in the radiator cap and a plastic recovery tank. A typical coolantrecovery system is shown inFigure 22. The recovery tank catches the

coolant that overflows the system when the radiator caps blow-offvalve opens. The vacuum valve in the center of the radiator cap diskallows coolant back into the system when the pressure drops.

I th t h i thi fi th t k i

FIGURE 22A typical cool-ant recovery system isshown here.



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Most recovery tanks have markings on them that indicate the coolantlevel. As you can see, this tank contains the marking COLD. Thismeans that when the engine is cold, the coolant level in the tankshould be at that level. Because an engine may not always be coolwhen youre checking the coolant level, many recovery tanks alsohave a HOT marking. This indicates the approximate coolant levelin the tank when the engine is hot. During routine maintenance, thecoolant level can easily be checked by using the marks on the coolantrecovery tank.

Once an engine is started, the coolant expands and raises the pressurein the cooling system. When the pressure becomes excessive, the pres-sure cap opens and allows some of the coolant to overflow out of theradiator and into the coolant recovery tank. Because the coolant flowsinto the recovery tank, its not lost, and the coolant can be used again

in the engine.

Later, when the engine cools down, the coolant stops expanding andbegins to return to its normalsmallervolume. As the coolant be-comes smaller in volume, the pressure in the system decreases, and avacuum develops in the system. The vacuum suction pulls open thesmall valve in the center of the radiator cap disk, and draws coolant

out of the recovery tank and back into the cooling system.

The valve in the radiator cap is a one-way check valve. That is, thevalve allows coolant to flow into the system, but not out of the system.The only way that coolant can flow out of the system is through the

blow-off valve in the pressure cap. Thus, the coolant recovery system

keeps the cooling system completely full of coolant, so the coolantlevel doesnt need to be checked as often.

Radiator Fans

As you learned, the radiator depends on air flowing through its core toremove heat from the coolant. Sometimes, an engine needs help blow-



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To ensure that all of the air blown by the fan actually passes throughthe radiator core, most fans are covered by afan shroud.The shroudsurrounds the outside of the fan and keeps any outside air away fromthe fan. A typical fan shroud is made of thin metal or plastic. The ac-tion of the fan shroud can be seen inFigure 24.Note how the shroudcompletely surrounds the fan, so that any air thats moved by the fan

must move through the radiator core.Automotive radiator fans can be driven in two different ways. The fanmay be operated by a small electric motor, or the fan may be driven bya rubber belt that connects it to a pulley on the end of the crankshaft.Lets take a look at each of these types of fans.

FIGURE 23A typical radia-tor fan assembly is shownhere. (Printed with permissionfrom the Honda Motor Co., Inc.)



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Electric Fans

Most newer automobiles contain electric radiator fan systems. In thistype of system, the fan is operated by a small electric motor thats at-tached to the center of the fan blades. The fans electric motor is oper-ated by the cars battery. When power from the battery is applied tothe fan motor, the motor rotates the fan blades and pulls air throughthe radiator core.

You may remember that an engine operates best within a specific op-erating temperature range, usually between 180 and 210 degrees Fahr-enheit. Because the engine isnt efficient if its operated below thistemperature, the radiator fan cant be allowed to operate all the time. Ifthe fan ran continually, the engine might become too cold, especially incold weather. However, when the engine temperature begins to rise,

the fan should begin to operate.

For these reasons, a cooling system needs a way to turn the radiatorfan on and off as its needed. This function is usually performed by acoolant temperature switch. A coolant temperature switch is tempera-ture-controlled, so the switch is mounted somewhere in the coolingsystem where its directly exposed to the coolant. The switch could bemounted almost anywhere in the system. However, in most cases, theswitch is mounted in one of the radiator tanks, or near the water outlet,where the hose attaches to carry water from the engine to the radiator.Figure 25shows a coolant temperature switch mounted in a radiatortank.

FIGURE 25In this fig-ure, you can see thecoolant temperatureswitch mounted in oneof the radiator tanks.



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On some engines, the coolant temperature switch operates even afterthe vehicle has been turned off. In such a vehicle, if the coolant is hotwhen the engine is turned off, the coolant switch keeps the radiator fanrunning until the coolant temperature decreases.

Belt-Driven Fans

Although most modern cars use electric fans, some vehicles still usebelt-driven fans. In a belt-driven radiator fan system, the fan blade is

usually attached to the end of the water pump shaft and is driven bythe samebelt that drives the water pump. A typical belt-driven fan isshown inFigure 26.Note how the fan blade is mounted to the end ofthe water pump shaft, and is driven by a rubber fan belt. The fan belt isconnected to the pulley on the crankshaft.

A belt-driven fan uses a radiator shroud much like the shroud on anl t i f H th h d d b lt d i f ll

FIGURE 26A typical belt-driven fan is shown here.



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so that the fan blades operates only when needed. If a belt-driven fanran continuously, the engine would take a long time to become warm,especially in cold weather.

The fan clutch design uses a fluid system that allows the fan blades tospin freely when the engine is cold. Then, when warm air from the ra-diator passes over the clutch hub, the hub warms and engages the fan

blades. When the fan blades are engaged, they rotate along with thecrankshaft. Then, when the air temperature cools down, the fan blades

are disconnected and allowed to rotate freely.

Its easy to determine if an engine uses this type of fan. Since the fanspins freely when the engine is cold, you can simply try to turn the fan

blades by hand. (Naturally, try this only when the engine is shut offand completely cooled). If the fan blades rotate easily, then the enginemost likely usesa fan clutch.Figure 27Ashows a cutaway side view ofa fan clutch, andFigure 27Bshows an end view of the fan clutch.

FIGURE 27Figure 27Ashows a cutaway side viewof a fan clutch, and Figure27B shows an end view of

the fan clutch.

(A) (B)



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radiator. In contrast, a transverse-mounted engine is mounted fromside to side in a vehicle. The front of a transverse-mounted enginefaces one side of the vehicle, far away from the radiator. Therefore,when a vehicle contains a transverse-mounted engine, it must use anelectric radiator fan.

Coolant System Hoses

On a typical vehicle, there are usually four major coolant systemhosestwo radiator hoses and two heater hoses. Radiator hoses con-nect the engine to the radiator. Heater hoses carry coolant to and fromthe heater core inside the passenger compartment. Radiator hoses arelarger in diameter than heater hoses. Radiator hoses usually measure

between 112and 2 12inchesin diameter,while heater hoses are usually1 2-,58-, or 34-inch in diameter.Figure 29shows an exploded view of the

FIGURE 28When a flex fan turns slowly, the fan spins and pulls air through the radiator. The fan blades areangled at this time, as shown in Figure 28A. However, once the vehicle is moving down the road and theengine speed increases, the thin, flexible fan blades flatten out, as shown in Figure 28B, and stop pulling asmuch air though the radiator.



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FIGURE 30 Th


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An engine may also contain a bypass hose that allows the coolant tocirculate inside the engine until the thermostat opens. This protects the

engine parts that heat rapidly, such as the exhaust valves, from beingdamaged. On some engines, the bypass is built into the engine, or theheater core is used as a bypass.

Cooling-system hoses are designed to slip over their connections onthe engine block or radiator, and are then held with special clamps

calledhose clamps. The most popular types of hose clamps are illus-trated inFigure 31.

FIGURE 30The upperhose carries coolantfrom the engine to theradiator, and the lowerhose carries coolantfrom the radiator back tothe engine. In most en-gines, the two hoses areattached as shown here.

FIGURE 31Coolant systemhoses are held in place byspecial clamps called hoseclamps. The most populartypes of hose clamps are il-

Th Th t t



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The Thermostat

Earlier in this study unit, you learned that an engine wont operateproperly if its too cold. If coolant began to circulate through a radiatoras soon as an engine was turned on, it would take a long time for theengine to become warm. In very cold climates, the engine might noteven reach its operating temperature. For this reason, the cooling sys-tem uses athermostatto help the engine warm up faster and to preventthe engine temperature from becoming too cold. The thermostat is

used to block the flow of coolant to the radiator when the engine iscold, which allows the engine to reach its proper operating tempera-ture faster.

An external cutaway view of a typical thermostat is shown inFigure 32. The thermostat contains a pellet of heat-sensitive material,

such as wax, sealed in a chamber with a piston at one end of the cham-ber. The piston connects to a valve or flap that closes the thermostat.

A thermostat is located at the cooling-system outlet that leads to the ra-diator where the warm coolant can pass under it and transfer heat to

FIGURE 32An externalcutaway view of a typicalthermostat is shown here.

Wh th i h it l ti t t th th



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When the engine reaches its normal operating temperature, the ther-mostat opens and coolant is allowed to pass, as shown inFigure 33B.

The location of the thermostat varies. However, in most cases, the ther-mostat is located at the top front of the engine, usually directly underthe location where the upper radiator hose connects to the engine. Thisconnection point is often called thethermostat housing. The thermostathousing is usually held in place with retaining bolts, and a gasket isused to seal the housing and prevent any coolant leakage. A typicalthermostat housing is shown inFigure 34.

FIGURE 33When an en-gine is cold, the thermostatblocks the flow of coolant,as shown in Figure 33A.

FIGURE 34A typicalthermostat housing as-sembly is shown here.

Temperature Gages



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Temperature Gages

In order to prevent engine damage, a driver must be notified immedi-ately if an engine is overheating. For this reason, every vehicle containssome sort oftemperature indicatoron its dashboard or instrument panel.The temperature indicator is designed to sense when the engine tem-perature is rising too high and send the temperature information to adisplay device on the vehicles instrument panel. There are two basictypes of temperature indicators: thetemperature gageand thewarning

light.

All modern temperature indicators are electric. An electric tempera-ture gage has an internal circuit that provides a gage reading based onthe amount of current that flows through it. When the ignition is on,electric current flows through the gage to a temperature sensor thats

installed in the engine block. The end of the sensor extends directlyinto a coolant passage. The location of a coolant temperature sensor isshown inFigure 35.

FIGURE 35The location ofa coolant temperature sen-sor is shown here. (Courtesy ofChrysler Corporation)

Warning lights rather than temperature gages are used in most mod



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Warning lights, rather than temperature gages, are used in most mod-ern vehicles. The warning light is installed in the instrument panel. Ifthe engine begins to overheat, the warning light simply lights up. A

warning light system contains a light bulb thats connected in serieswith a mechanical temperature sensor(Figure 36).Current can flowthrough the light only when the circuit is grounded. The sensor is a

bimetallic spring thats set to move when a preset temperature isreached. If the engine starts to overheat, the coolant temperaturereaches the preset sensor temperature. This causes the bimetallic

spring to move, and the spring then contacts and grounds the electricconnector from the light circuit. This completes the electric circuitthrough the light bulb, causing it to light up. The warning-light bulbalmost always contains a red lens so that the light cant be missed bythe driver.

Most modern vehicles contain warning lights because the lights aredifficult to overlook or ignore. The average driver often forgets tocheck gages, or may even be unaware of how to interpret the gagereadings. For this reason, the simple warning light is the quickest wayto warn the driver that something is wrong in the cooling system.

FIGURE 36A warning-lightsystem contains a light bulbthats connected in serieswith a mechanical tem-perature sensor, as shownhere. Note how the tem-perature sensor is mountedso its in direct contact with

the coolant.



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FIGURE 37A typical liquid-cooling system for a V-type engine is shown here. The arrows indicate the di-rection of the flow of coolant throughout the system. Note that this system has a cross-flow radiator. (Usedwith permission of Madza North American Operations)

Since the thermostat is closed at this point, the engine quickly reaches



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Since the thermostat is closed at this point, the engine quickly reachesits normal operating temperature when its turned on. Once the enginereaches its operating temperature, the thermostat opens and the cool-

ant flows through the radiator. In the radiator, the coolant is cooledbefore it reenters the engine.

The coolant flow shown inFigure 38is typical of that in most modernengines. The coolant enters the engine from the bottom of the radiator,and then passes through the water pump and into the lower part of the

water jacket in the engine block. Next, the coolant flows up throughthe water jacket and cylinder head, and exits out of the top of the en-gine. The coolant then passes by the thermostat and reenters the radia-tor. However, note that the coolant reenters at the top of the radiatorrather than at the bottom. Finally, the coolant flows through the radia-tor core to the bottom of the radiator, where it leaves the radiator andreenters the engine to remove more heat.

bottom of the water jacket. Reverse-flow cooling systems are used by



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j g y yonly a few vehicle manufacturers. The operation of the reverse-flowsystem is the same as that of the other system we discussedthe only

difference is the direction in which that the coolant flows.

Air-Cooling Systems

So far, youve learned about liquid-cooling systems. However, liquid

cooling isnt the only type of system thats used to keep automotive en-gines cool. Over the years, a few automobiles have contained air-cooling systems. Air-cooling systems use no liquid coolant at all. In-stead, only a flow of air across the outside of the engine is used forcooling.

Air-cooling systems are simple, both in construction and in operation.The engine parts that get the hottest are the cylinders and the cylinderheads, so the air-cooling system uses a fan to force air past these com-ponents. Heat is then transferred from the engine to the forced air byconvection.Figure 39shows an illustration of the operation of an air-cooling system.

The air-cooled engine has several design features that distinguish it



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g g gfrom the liquid-cooled engine.

The cylinders and cylinder heads are finned to increase theiroverall surface area, which allows more surface to be cooled bythe air(Figure 40).

The fan, sometimes called a blower, is belt-driven from the en-gines crankshaft.

The engine and fan are usually shrouded by sheet metal so thatmore air can be directed over the hottest parts of the engine.

Most air-cooled engines have an extra oil cooler, which transfersheat from the oil directly into the air stream.

The air-cooled engine has several advantages over the liquid-cooled en-gine. A typical air-cooled engine will run about 20 degrees Fahrenheithotter than an equivalent liquid-cooled engine. This increased operatingtemperature improves gas mileage and the operation of the emission

control system. An air-cooled engine has fewer cooling-system parts and

FIGURE 40In this cutawayview of an air-cooled V-type engine, you canclearly see the fins on thesurfaces of the cylinders.

Now, take a few moments to review what youve learned by complet-



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ingPower Check 2.

Power Check 2


_____ 1. In most engines, the water pump is mounted to the engines front cover and isdriven by the crankshaft.

_____ 2. A V-type engine usually contains one block drain plug, while an in-line engineusually contains two block drain plugs.

_____ 3. Like an oil pump, a water pump pressurizes the coolant and circulates itthrough the various passages in the cooling system.

_____ 4. A serpentine belt is much wider, thinner, and longer than a typical V-belt.

_____ 5. A typical vehicle usually contains four radiator hoses and two heater hoses.

_____ 6. When an engine reaches its proper operating temperature, the thermostat closesand blocks the flow of coolant out of the engine.

_____ 7. One V-type belt can drive several engine accessories at the same time.

8. In a serpentine drive belt system, the component that holds the belt at its proper ten-sion at all times is called the _______.

9. The openings at the ends of the machined coolant passages in the engine block aresealed with _______.

10 The opening at the top of a radiator tank that holds the radiators pressure cap is called



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COOLING-SYSTEM MAINTENANCE

As you know, the purpose of the cooling system is to keep the engines

temperature within a specific range. However, in order to do this, the

Power Check 2

13. In a vehicle that uses an electric radiator fan, the fan is operated by a small electric mo-tor that gets its power from the cars _______.

14. Radiator and heater hoses are designed to slip over their connections, and then areheld with _______.

15. The two basic types of temperature indicators are the temperature gage and the_______.

16. The coolant thats released by the pressure cap flows through an overflow tube to the_______.

17. In many coolant recovery systems, the recovery tank is mounted right next to the_______.

18. In a typical cooling system, the upper radiator hose carries the coolant from the engineto the radiator, and the _______ radiator hose carries coolant from the radiator back tothe engine.

19. A small valve called a _______ is located at the bottom of a radiator tank and is used todrain the coolant from the radiator for servicing.

Check your answers with those on page 99.

Checking the Coolant Level



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g

A proper coolant level is necessary to keep an engine at its proper op-erating temperature. The cooling system performs best when its com-pletely filled with coolant. Its also very important to get all of the airout of the system whenever you add coolant. If the coolant level is toolow, or if air gets into the system, the cooling system wont work effi-ciently. The air in the system may cause some coolant to be forced outeach time the engine is shut off.

Remember that a cooling system is pressurized when an engine be-comes warm. Since the coolant is a liquid, and liquids can't be com-pressed, the pressure affects only the boiling point of the coolant.However, air can be compressed. If the cooling system has air in it, theair tends to form a pocket at the highest point in the system. Then, as

the system is pressurized, this air is compressed, and the overall cool-ing-system pressure is less than normal. This lowered pressure causesthe boiling point of the coolant to be lowered.

When the engine is shut off, the air pocket expands, much like a largespring. As the air expands, it takes up more space in the system,thereby increasing the system pressure. When the pressure increases to

a certain point, the pressure cap forces some coolant out into the over-flow tube and into the coolant recovery tank to relieve the pressure.However, because of the air in the system, the coolant wont be drawn

back into the radiator once the engine cools down.

You learned in the last section that most modern engines use coolant

recovery systems. If an engine has a coolant recovery system, its rela-tively easy to check the coolant level. First, locate the plastic coolant re-covery container. These containers are usually semitransparentthatis, you can see through the side of the container to check the level ofthe coolant inside. To check the level, simply look at the side of thecontainer to see the coolant level. Then, match this level to the mark-ings on the side of the recovery tank. Most recovery tanks have twomarkings. One marking indicates the proper coolant level when the

Note: Never fill a coolant recovery tank to the very top, particularlyh i i ld If th t k i fill d t th t th



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when an engine is cold. If the recovery tank is filled to the top, thecoolant thats released from the hot engine has nowhere to go. This

causes the recovery tank to overflow, and coolant leaks out of the topof the tank. Although this probably wont harm the engine, it couldalarm the driver, who may believe that the system has a leak.

To check the coolant level on an older engine that doesnt have a cool-ant recovery system, remove the radiator cap and check the coolant

level directly at the radiator. You can also do this with a vehicle thathas a coolant recovery system, if you suspect that the vehicle is low oncoolant or has a leak. Either of these conditions may prevent coolantfrom being drawn back into the system from the recovery tank. There-fore, even if the recovery tank contains coolant, it doesn't always meanthat the rest of the system is full.

Before you remove a radiator cap to check the coolant level directly atthe radiator, you must follow several safety precautions. Rememberthat the coolant in a vehicle is often very hotover 200 degrees Fahr-enheitat times. In addition, the coolant is under pressure. Therefore,you must not remove a radiator cap until the engine and cooling sys-tem have cooled completely. If you attempt to remove the radiator cap

from a vehicle when it's hot, the pressurized coolant will spray out allover your hand and arm when the cap is released. The very hot cool-ant can severely burn your skin.

Remember that the pressure in the system helps raise the boiling pointof the coolant. When the coolant is under pressure, the boiling point ishigh enough to keep it from boiling. However, as soon as the cap is re-moved and the pressure is released, the boiling point of the coolant isinstantly lowered. Therefore, if an engine is very hot, the coolant will

boil quickly when you open the cap and a hot vapor will be forced outof the filler neck. This vapor can burn you severely.

To avoid injury, wait until the coolant has cooled completely. When an

engine is cold, theres very little, if any, pressure in the cooling system,

Step 3: Turn the radiator cap one-quarter turn counterclockwise, oruntil it stops When you turn the cap one quarter turn the



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until it stops. When you turn the cap one-quarter turn, thepressure in the system is released, but the cap wont come all

the way off. The cap is designed this way so that if any pres-sure remains in the system, coolant is prevented from flow-ing out around the cap when its loosened. Since the cap isstill attached, it deflects the coolant away from your hand.

Step 4: Once the pressure has been released, push in on the cap

while you continue to turn it counterclockwise. After aboutone-half turn, the cap can be lifted off the radiator.

Once the radiator cap is off, you can check the coolant level in the ra-diator.

In a vehicle that uses a coolant recovery system, the radiator should becompletely filled to the top with coolant, whether the engine is cold orwarm. In a vehicle that doesnt use a coolant recovery system, the ra-diator should be filled with coolant to the top if the engine is warm. Ifthe engine is cold, pour in coolant to about one inch below the top ofthe filler neck in a top-flow radiator, and to about three inches belowthe top of the filler neck in a cross-flow radiator(Figure 41). Remem-

ber, if a vehicle doesnt have a coolant recovery system, some space isneeded for the coolant to expand when the engine is hot. This is whythe radiator in such a vehicle isnt filled to the very top when the en-gine is cold.

FIGURE 41In a vehiclethat doesnt use a cool-ant recovery system,when the engine is cold,the radiator should befilled with coolant toabout one inch below thetop of the filler neck in a

top-flow radiator, andb t th i h b l

running, though, this task is dangerous and should be performed onlywith extreme caution Observe all safety procedures and wear gloves



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with extreme caution. Observe all safety procedures, and wear glovesto protect your hands from the hot coolant.

Adding Coolant to an Engine

Coolant is usually added to both the radiator and the coolant recoverytank until both levels are correct. When adding coolant to an engine, be

sure to use a 50-50 mix of antifreeze and water. Adding plain water toa system dilutes the coolant mixture and reduces its ability to protectthe engine against severe temperatures and corrosion.

If an engine is warm when youre adding coolant, its a good idea toadd the coolant while the vehicle is running. This causes the new cool-ant to quickly mix in with the coolant thats already in the system. Italso prevents the new coolantwhich is relatively coldfrom cominginto direct contact with the hot engine components, such as the radia-tor and engine block. A sudden temperature change could cause thesecomponents to crack.

Testing the Coolant

Its very important to check the percentage of antifreeze in a coolingsystem at least once a year. Even if you live in an area where the tem-perature never falls below freezing, the antifreeze percentage is stillvery important for cooling purposes. Antifreeze also contains the cor-

rosion inhibitors that an engine needs. Very old antifreeze wont haveany corrosion inhibitors left, and the cooling system is therefore un-protected. This can cause rusting and sludge buildup in the coolingsystem, which reduces the cooling abilities of the system. Once a cool-ing system becomes badly rusted, its almost impossible to clean it orrestore it to its original condition.

Thus you should test a sample of coolant from a vehicle on a regular ba-

green doesnt mean that it contains enough antifreeze to protect the en-gine The color is similar whether it contains a lot of antifreeze or just a



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gine. The color is similar whether it contains a lot of antifreeze or just alittle. The only truly accurate way to determine its strength is to use a

coolant tester specifically designed for this purpose.

The most common type of coolant tester is the hydrometer.Several dif-ferent types of hydrometers can be usedto test antifreeze. One com-mon type of hydrometer is illustrated inFigure 42.This tester consistsof a glass tube with a free-floating weighted bulb inside, a hose, and a

rubber bulb at the top of the tester.

To test a sample of coolant from a cooling system place the hydro-

FIGURE 42A typicalhydrometer is illus-trated here.

Another type of hydrometer contains a plastic needle that floats in thecoolant. A sample of coolant is drawn from the engine in the same way



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coolant. A sample of coolant is drawn from the engine in the same waywe described previously. Then, the amount of protection is read by

matching the point on the needle to the scale thats marked on the out-side of the tester.

A third type of tester thats used to test antifreeze is called afloating-balltester. In this tester, several small, weighted balls are placed in a glasstube. A sample of the coolant is drawn up into the tester. Once the cool-ant is in the tester, the tester is held straight up and down, and a numberof balls float up into the coolant sample to indicate the protection level ofthe coolant. You then count the number of balls, and match the numberto a chart on the tester to determine the protection level.

If a coolant sample test indicates that the coolant mixture doesnt con-tain enough antifreeze, drain some of the coolant from the vehicle, and

then add some straight antifreeze to the cooling system. Then, retestthe mixture to be sure the percentage of antifreeze in the coolant iscorrect.

Changing the Coolant

To keep the cooling system operating at its best, many manufacturersrecommend that the coolant in a system be changed at least once ayear. To change the coolant, the old coolant needs to be drained fromthe vehicle. The system is then flushed to clean out the coolant pas-sages, and then refilled with new coolant. Lets begin with how todrain the coolant from a vehicle.

Draining a Cooling System

Before you can begin to drain a cooling system, you need an appropri-ate container. Most cooling systems hold about two or three gallons ofcoolant, so the container should be able to hold at least that much. Spe-cial containers calleddrain pansare available at most auto supply

stores These containers are large and relatively flat so they can easilyb l d d hi l h h l i d i D i

Step 2: Begin with a cold engine thats turned off. Locate the drainpetcock on the radiator, and the block drain plugs on the en-



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p , p ggine block. The radiator petcock is located near the bottom

of one of the radiator tanks, and the block drain plugs are lo-cated on the side of the engine block. If you have difficultylocating these items, the service manual for the vehicle usu-ally indicates their locations.

Step 3: Place the container under the radiator drain petcock.

Step 4: Open the radiator drain petcock. You can usually turn thepetcock by hand; however, if its very tight, you may have toturn it with a pair of pliers. Once the petcock is opened, thecoolant will begin to drain out of the radiator and into thedrain pan. At this point, keep the radiator cap on. By leaving

the cap on, you can test to see that the coolant recovery sys-tem is working properly. As the coolant drains out, suctionwill be created in the system. If the recovery system is work-ing properly, the suction will pull all of the coolant from therecovery tank into the cooling system. This is a good way todrain the old coolant from the recovery tank so that the cool-ant can be replaced.

If the vehicle doesnt have a coolant recovery tank, open the drain pet-cock and the radiator cap to drain the coolant.

As the coolant drains out, be sure that it enters the drain pan. Adjustthe position of the pan if necessary to prevent coolant from spilling

onto the floor or ground. If any coolant is spilled, clean it up immedi-ately and flush the area with clean water.

Step 5: When the coolant recovery tank is empty, remove the radia-tor pressure cap and allow any remaining coolant to drainout of the radiator petcock.

Remember that V-type engines usually have two separate block drainplugs, one on each side of the engine. Therefore, in a V-type engine,



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p g g yp gyou need to repeat this step on the other side of the engine.

Flushing a Cooling System

Once the cooling system has been completely drained, you shouldflush the system to clean out any dirt and debris that may be in thecoolant passages. Flushing is a procedure in which water or cleaning

solution is forced through the system to flush out dirt and debris. Thesystem can be flushed with a chemical cleaning solvent, or you canreverse-flush the system with water.

Lets look at the cleaning-solvent method first. A commercial cleaningsolvent, such as Prestone Super Flush, removes rust, grease, and dirtfrom the coolant passages better than plain water. Cooling-systemcleaning products are made by many manufacturers and can be pur-chased at any automotive-parts store. Most brands come in more thanone strength. A regular-strength cleaner can be used in a system thatsrelatively free of rust and debris, while a heavy-duty cleaner can beused in a neglected system that has a buildup of rust and corrosion.

To check the condition of the cooling system, remove the pressure capand look into the radiator filler neck. When you look into the radiator,you should be able to see some of the small tubes that run through theradiator core. If you can see that a lot of rust and corrosion are block-ing the ends of these tubes, then youll know that the cooling systemneeds a thorough cleaning.

Commercial chemical cleaners are relatively easy to use. When usingthese cleaning products, be sure to carefully follow the directions onthe package. The exact cleaning procedure may vary depending on the

brand of cleaner you use; however, in most cases, you can follow thesesteps:

Step 1: Drain all of the coolant from the system

Step 7: Drain the system again.



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Step 8: Close the petcock and reinstall the block drain plugs.

Step 9: Since the cleaning solvent is usually an acidic liquid, the sys-tem must now be rinsed with clean water to remove any sol-vent that remains. Fill the system with plain water.

Step 10: Run the engine for about five minutes or so to circulate thewater through the system.

Step 11: Stop the engine and allow it to cool.

Step 12: Open the radiator petcock and block drain plugs, and drain

the water from the system.

Step 13: Once the water is drained from the system, close the petcockand install the block drain plugs.

Step 14: Refill the system with new coolant.

As you can see, cleaning a cooling system with a commercial cleaningproduct is a relatively easy process.

Now, lets look at the reverse-flushing method of cleaning a coolingsystem. In the reverse-flushing procedure, water is forced through thecooling system with air pressure, in the direction opposite to that ofthe normal flow of water. This process allows water to get behind andunderneath rust deposits that couldnt otherwise be removed. A toolcalled aflushing gunis used to reverse-flush the system. Flushing gunscan be purchased at an automotive-parts store. The flushing gun hastwo connectionsone for water and one for compressed air. There-fore, you must have a compressed-air source in your shop to use a

flushing gun


FIGURE 43In this illus-tration, a radiator is be-ing cleaned by


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Step 4: Continue this procedure until the water from the radiatorruns clear.

When you reverse-flush a cooling system, you should also reverse-flush the engine block to remove any rust deposits it may contain. Thefollowing is a typical procedure for reverse-flushing an engine block.

Step 1: Drain the radiator and disconnect the hoses at the radiator.

Step 2: Remove the thermostat housing and the thermostat from theengine block, and then reinstall the thermostat housing.

Step 3: Attach a suitable flushing gun to the thermostat housinghose connection.

Step 4: Turn on the water and fill the engine block.

Step 5: Turn on the compressed air in short blasts, as shown inFigure 44. Continue this procedure until the water from theengine runs clear.

ing cleaned byreverse-flushing with

water and air pressure.

FIGURE 44The internal

passages of the engine

Step 7: Reconnect the radiator hoses.

h h



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Step 8: Refill the cooling system with new coolant.

Refilling a Cooling System

Once the cooling system has been flushed, you can add new coolant tothe system. To refill the system with coolant, slowly pour the coolantinto the radiator through the filler neck. Its a good idea to use a funnel

to help with this process, as shown inFigure 45. Remember that youneed to fill the system with at least a 50-50 mixture of antifreeze andwater.

To make sure youre adding enough antifreeze, check the service man-ual to determine how much coolant the system holds. For example, ifthe system holds eight quarts of coolant, then you know that youshould add at least four quarts of antifreeze and four quarts of plainwater. This method works well if you know how much coolant thesystem holds.

If youre not sure how much coolant the system holds simply mix the

FIGURE 45Using a fun-nel makes it easier toadd coolant to thesystem.

the manufacturers service manual. The protection level of the anti-freeze should be at least 10 degrees Fahrenheit lower than the lowest

t d t t i



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expected temperature in your area.

Once youve determined the proper amount of antifreeze needed, fillthe system. The following is a general procedure that can be used to fillthe cooling system in most vehicles.

Step 1: With the engine turned off, add coolant to the radiator at thefiller neck. Fill the system until the level is about one inch be-low the filler neck. Be sure to pour the coolant into the en-gine slowly so that any air in the system is allowed to exit.

Step 2: Start the engine and allow it to idle. Once the engine starts,you may see the coolant level drop slightly. Then, as the en-gine warms up, the coolant level often rises once again as thecoolant warms and expands. At this point, remember thatthe thermostat is closed. Because the thermostat is closed,the system isnt completely full. Air thats trapped in the en-gine block cant escape the system until the thermostatopens and the coolant flows through the entire system.

Step 3: Allow the engine to heat upwith the radiator cap leftoffuntil the thermostat opens. At this time, move the con-trol for the heater in the passenger compartment to the hotor high position. Remember that some of the coolant fromthe engine is used to provide heat to the passenger compart-ment. By moving the heater control to the hot position,

coolant is allowed to flow through the heating system andremove any air thats trapped in the heater core.

Step 4: When the thermostat opens, the coolant level drops quicklyas the air is allowed to escape, and coolant can now fill theengine block. If you look in the filler neck, you'll see that the

coolant in the radiator is now flowing where previously itd ll I f h h ll h

Step 6: Now that the system is completely full, you can install theradiator pressure cap. Its best to install the cap while the en-gine is still running If the engine is shut off with the pres



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gine is still running. If the engine is shut off with the pres-

sure cap off, coolant can be pushed up out of the radiator,leaving an air space behind. However, if the cap is in placewhen the engine is shut off, all of the coolant will remain inthe system.

Step 7: If the vehicle has a coolant recovery system, mix and add

coolant mixture to the recovery tank up to the maximummark on the tank. Its important to fill this tank with coolantand not just plain water. Plain water freezes in the recoverytank in cold weather, and prevents the system from workingproperly.

Step 8: When the vehicle has cooled down, remove the radiator capagain and use a coolant tester to test the protection level ofthe coolant. If you've added the proper amount of antifreeze,the protection should be adequate. However, it doesnt hurtto double-check to make sure that the coolant protection isadequate for the vehicle and the local climate.

You may wonder how all the air gets out of the cooling system whenyoure filling it. Well, air always tends to move to the highest point inthe system. In most vehicles, the highest point of the cooling system isthe radiator filler neck. So, once an engine is warm and the coolant be-gins to circulate, any air in the system tends to move up to the fillerneck. Since the radiator cap is off when you fill a cooling system, the

air escapes out of the filler neck. This is the reason why the cap is keptoff the radiator when you fill the system.

In some vehicles, however, the filler neck may not be the highest pointin the cooling system. Instead, the highest point in the cooling systemmay be the top of the engine. This type of engine contains a specialair

bleed valve at the very top of the water passages usually in or near the


FIGURE 46In someengines, a special airbleed valve is used to


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Handling Antifreeze

As you learned earlier in this study unit, some types of antifreeze arepoisonous. For this reason, antifreeze must be disposed of very care-fully. In some areas, antifreeze can be dumped into a traditional waterdrainage system since the water dilutes the antifreeze enough to make

it harmless. However, some municipalities have regulations regardingthe dumping of antifreeze into drainage systems. This is because usedantifreeze may contain small amounts of gasoline and other contami-nants that can harm the environment. So, check with your local watercompany or your local auto parts store to find out how to properly dis-pose of antifreeze in your area.

Many larger automotive repair shops now use special machines to col-lect old antifreeze and clean it so that it can be recycled. A typicalcool-ant recovery and recycling machineis shown inFigure 47. Coolantrecovery and recycling machines are usually quite expensive, sotheyre usually used only in larger shops that do a lot of coolant servic-ing. However, many auto parts stores are now installing these ma-

chines so their customers can easily dispose of old antifreeze

remove air from the

cooling system whenyoure filling it withcoolant. (Printed with permis-sion from Honda Motor Co., Inc.)


FIGURE 47A typicalcoolant recovery andrecycling machine is

h h


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Now, take a few moments to review what youve learned by complet-ingPower Check 3.

Power Check 3


_____ 1. Coolant should be drained from a system when the engine is warm andrunning

shown here. (Courtesy of

Snap-On Tools Co., CopyrightOwner)


Power Check 3


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_____ 7. In order to clean a cooling system with a chemical solvent, you need to drain allof the coolant from the system, and then reinstall the drain petcock and the blockdrain plugs.

_____ 8. To keep the cooling system operating at its best, the coolant should be changedat least once a year.

_____ 9. Most cooling systems hold between five and six gallons of coolant.

_____10. To drain the coolant from a radiator, you should remove the radiator cap beforeyou open the radiator drain petcock.

_____11. V-type engines have two separate block drain plugs, one on each side of the en-gine block.

_____12. If a coolant sample is very green, you can be sure that the cooling system hasenough antifreeze in it.

13. When youre reverse-flushing a cooling system, the flushing gun is attached at the ra-diators _______ hose connection.

14. When a flushing gun is used to clean a cooling system, the internal radiator pressuremust not exceed _______ psi.

15. You can check for rust and corrosion in a cooling system by removing the pressure capand looking into the _______.

16. The most common type of coolant tester is the _______.

17. The percentage of antifreeze in a cooling system should be checked at least once a_______

18. To drain the coolant from a radiator, you need to open the _______ near the bottom ofone of the radiator tanks.

INSPECTING, TESTING, AND REPAIRING A COOLINGSYSTEM



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When you change the coolant, you should inspect other cooling-system components for damage or wear. These components in

Study Unit - Automotive Cooling Systems

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