Ch 17 Cooling System

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Cooling Systems Theory and operation Components

Thermostat Hoses Radiator Radiator cap Coolant recovery Fans Water pumps

Anti-freeze


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Theory and Operation

The cooling system

removes excess heat tokeep the inside of theengine at an efficienttemperature, about 200o F

(94o

C).

Animation: Cooling System
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Coolant FlowCoolant flows through thewater jackets where it

absorbs heat. It then flowsthrough the radiator whereheat is transferred to the airpassing through. The amount

of flow is determined by thewater pump. The flowdirection is controlled by thethermostat.


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Cold Engine

When an engine is cold, the

thermostat is cold. Coolantflow is through the bypasshose and the water jackets.This allows the engine to

warm up evenly.


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Warm Engine

The thermostat openswhen the engine warms up.This allows coolant tocirculate through the

radiator and the waterjackets.


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Theory and Operation Maintains operating temperature of

approx. 200-235 degrees

When temperature is low, bypass blockscoolant flow through radiator

When correct temperature is reached,

thermostat opens and excess heat isabsorbed through water jackets andpassed on to air flowing throughradiator


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Problem:A cylinder head has been removed from an

engine

Two exhaust valves are badly burned The head is warped

Coolant is in combustion chambers

What caused this problem? What should be done to repair this?


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Thermostat

The spring in this thermostat has

closed the valve. When it getshot, the heat motor will push thevalve open.

Animation: Thermostat Operation


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Thermostat Operation Where is it located?

How does it control the enginestemperature?

Can it be installed incorrectly?

How often should it be replaced?


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Thermostats


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What if What is likely to happen if the

thermostat were removed from a

vehicle?


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Hoses

Reinforced rubber hoses transfer the

coolant from the engine to the radiator,coolant reservoir, and heater core.


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Hoses and Clamps


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Hoses Why are hoses necessary?

How often should they be replaced?

Why do some hoses have internalsprings and what would happen if theywere removed?

Why are hose clamps so critical to theoverall operation of the cooling system?


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Radiator

The hot coolant flows through theradiator tubes and heat is transferred

to the fins and then to the air passingthrough radiator.


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Radiator Types

Older vehicles used downflow

radiators with the coolantflowing from the top to thebottom. Modern vehicles usecrossflow radiators with thecoolant flowing from one side to

the other.


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Radiator Composition Soldered copper or brass

Repairable

Aluminum cores with plastic tanks

Lighter weight

Corrosion resistant

More inexpensive

Better heat transfer


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Problem:A plastic/aluminum radiator is leaking at

its seam

How can it be repaired?

What is the main advantage of acrossflow radiator over a downflowradiator?


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Radiator Cap

The upper gasket prevents coolant

from escaping to the outside. Thelower gasket keeps a pressure inthe radiator. The cam lock pushesthe two gaskets against the sealingsurfaces when the cap is installed.

The safety stop prevents the capfrom being opened too quickly.

Animation: Pressure Cap


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Radiator Pressure

Radiator pressure results from the expansion of the

coolant as the engine warms up.

The radiator cap creates the pressure by holding the

coolant in the radiator.

Coolant volume increases about 10% as thetemperature increases from 70 to 180o F (21 to 82o C).

The coolants boiling point increases about 3o F foreach psi increase in pressure.


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Coolant Recovery Reservoir

When the engine warms up, theradiator cap allows theexpanding coolant to flow intothe coolant recovery reservoir.

When the engine and coolant cool

down, the coolant returns to theradiator and water jackets throughthe vacuum valve in the cap.


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What will happen if:A customers vehicle has a very slight

leak at the thermostat housing?

What symptoms would the customermost likely notice?


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Radiator Cap Types

These caps are the sameexcept for the vacuum valve.This valve opens to allow

coolant to return from theCRR. The gravity vacuumvalve opens much easier.


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Problem: If a customers pressure cap is

defective, what is the most likely

symptom the customer would notice? How often should a pressure cap be

replaced?


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What will happen if:At normal operating temperature, you

remove the radiator pressure cap to

check coolant level?

How can the coolant level be checked

safely?


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Checking coolant level


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Radiator Air Flow

Air flows through the openings at

the front of the vehicle, throughthe radiator and other heatexchangers, and exits past theengine. The fan with shroud

assists the natural flow when thevehicle goes slow or is stopped.


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Fan and Fan Drive

Most rear wheel drive vehicles use a

mechanically driven fan that ismounted onto the water pump.

Some vehicles use a hydraulic

cooling fan


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Fan Clutch

The fan clutch allows theuse of a large fan that canbe driven at slower speeds.A thermal fan clutch senses

temperature and will drivethe fan only when itbecomes necessary.


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Electric Fans

Most front wheel drive vehicles use

fan that is driven by an electricmotor. This fan assembly includesthe motor, fan, and shroud.

Some vehicles use two fans andsome of these have two speeds.


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Electric Fans Electric fans can be mounted in front of

or behind the radiator or combined

Electric fans are controlled by relaysthat are energized by a vehicles PCM


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Problem: How can an electric fan circuit be

tested?


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Fans Why would a hydraulic cooling fan be

advantageous over a traditional fan

clutch? Why is fan operation so closely

controlled on a vehicle?

How can a fan clutch be tested?


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Drive Belt

The water pump and fan are driven

by a flexible accessory drive belt thatis driven by the crankshaft pulley.


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Water Pump Water pumps are centrifugal pumps

Some pumps are driven by accessory

drive belts

Some pumps are driven by enginetiming belts

Some pumps are driven by the enginetiming chain


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Water Pumps Weep holes:

Holes placed in bearing housing to keep

coolant from infiltrating bearing Weep hole allows any anti-freeze that

passes by seal to exit bearing housing

If seal deteriorates, coolant will leak out ofweep hole


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Water Pumps How often should a weep hole be inspected

for leakage?

How can leakage be detected? What would happen if the leak was ignored

and vehicle continued to operate?

Why is water pump replacement wise on anapplication where the pump is driven by thetiming belt?


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Coolant and AntifreezeCoolant is a mixture of antifreezeand water. Antifreeze lowers the

freezing point and raises theboiling point.

Coolant also protects the system

from rust and corrosion.


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Anti-freeze Coolant life is determined by the life of

the corrosion protection package

Older conventional coolants (IATs)should be changed every two years

Newer extended life coolants (OAT/

HOATs) should be changed every fiveyears


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Anti-freeze IAT: inorganic additive technology

OAT: organic acid technology

HOAT: hybrid organic acid technology

Extended and conventional anti-freezescannot be mixed

EG: ethylene glycol

PG: propylene glycol


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Anti-freezeAll anti-freezes contain:

Corrosion inhibitors: silicates, phosphates,

borates pH buffers: maintain acid-alkaline balance,

prevent electrolytic corrosion

EG or PG base: to reduce freezing pointand increase boiling point

Dye: to distinguish anti-freeze and type


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Anti-freeze Maximum concentration: 67% anti-

freeze

Minimum concentration: 50% forcorrosion prevention

Pure anti-freeze has higher viscosity

and does not flow well Does not transfer heat well

Ch 17 Cooling System

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