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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 to keep the inside of the engine at an efficient temperature, about 200o F (94o C).

Animation: Cooling System

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Coolant Flow

Coolant flows through the water jackets where it absorbs heat. It then flows through the radiator where heat is transferred to the air passing through. The amount of flow is determined by the water pump. The flow direction is controlled by the thermostat.

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Cold Engine

When an engine is cold, the thermostat is cold. Coolant flow is through the bypass hose and the water jackets. This allows the engine to warm up evenly.

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Warm Engine

The thermostat opens when the engine warms up. This allows coolant to circulate through the radiator and the water jackets.

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Theory and Operation Maintains operating temperature

of approx. 200-235 degrees When temperature is low, bypass

blocks coolant flow through radiator

When correct temperature is reached, thermostat opens and excess heat is absorbed through water jackets and passed on to air flowing through radiator

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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 gets hot, the heat motor will push the valve open.

Animation: Thermostat Operation

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Thermostat Operation Where is it located? How does it control the engine’s

temperature? 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 internal

springs and what would happen if they were removed?

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

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Radiator

The hot coolant flows through the radiator tubes and heat is transferred to the fins and then to the air passing through radiator.

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Radiator Types

Older vehicles used downflow radiators with the coolant flowing from the top to the bottom. Modern vehicles use crossflow radiators with the coolant 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 it’s seam How can it be repaired?

What is the main advantage of a crossflow radiator over a downflow radiator?

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Radiator Cap

The upper gasket prevents coolant from escaping to the outside. The lower gasket keeps a pressure in the radiator. The cam lock pushes the two gaskets against the sealing surfaces when the cap is installed. The safety stop prevents the cap from 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 the temperature increases from 70 to 180o F (21 to 82o C).

The coolant’s boiling point increases about 3o F for each psi increase in pressure.

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Coolant Recovery Reservoir

When the engine warms up, the radiator cap allows the expanding coolant to flow into the coolant recovery reservoir.When the engine and coolant cool down, the coolant returns to the radiator and water jackets through the vacuum valve in the cap.

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What will happen if: A customer’s vehicle has a very

slight leak at the thermostat housing?

What symptoms would the customer most likely notice?

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Radiator Cap Types

These caps are the same except for the vacuum valve. This valve opens to allow coolant to return from the CRR. The gravity vacuum valve opens much easier.

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Problem: If a customer’s 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, through the radiator and other heat exchangers, and exits past the engine. The fan with shroud assists the natural flow when the vehicle goes slow or is stopped.

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Fan and Fan Drive

Most rear wheel drive vehicles use a mechanically driven fan that is mounted onto the water pump.

Some vehicles use a hydraulic cooling fan

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Fan Clutch

The fan clutch allows the use of a large fan that can be driven at slower speeds. A thermal fan clutch senses temperature and will drive the fan only when it becomes necessary.

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Electric Fans

Most front wheel drive vehicles use fan that is driven by an electric motor. This fan assembly includes the motor, fan, and shroud.

Some vehicles use two fans and some 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 relays that are energized by a vehicle’s 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 that is 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 engine

timing belts Some pumps are driven by the

engine timing 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 of weep 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 an application where the pump is driven by the timing belt?

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Coolant and Antifreeze

Coolant is a mixture of antifreeze and water. Antifreeze lowers the freezing point and raises the boiling 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 (IAT’s) should be changed every two years

Newer extended life coolants (OAT/ HOAT’s) should be changed every five years

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Anti-freeze IAT: inorganic additive technology OAT: organic acid technology HOAT: hybrid organic acid

technology Extended and conventional anti-

freezes cannot be mixed EG: ethylene glycol PG: propylene glycol

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Anti-freeze All anti-freezes contain:

Corrosion inhibitors: silicates, phosphates, borates

pH buffers: maintain acid-alkaline balance, prevent electrolytic corrosion

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

Dye: to distinguish anti-freeze and type

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Anti-freeze Maximum concentration: 67% anti-

freeze Minimum concentration: 50% for

corrosion prevention Pure anti-freeze has higher

viscosity and does not flow well Does not transfer heat well