ch 17 cooling system
TRANSCRIPT
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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