1. The Cooling System (Reasons for)
Approximately only 35% of the heat energy produced by the burning of the fuel is converted into useful energy.
The remaining heat must be removed from the engines components or they would get so hot, they could seize and possibly melt.
Liquid or Air Cooling are the two main systems used

2. Engine Cooling (movement of heat)
Heat always moves from a hot area to a cooler area by three different ways.
CONDUCTION – heat moves through solids materials, normally metals.
CONVECTION – heat can be moved by moving liquids or gases.
RADIATION – Heat given off by an object is carried away by the surrounding air.

3. Cooling System
Combustion temperatures in cylinders up to 2500ºC (4500ºF).
Normal coolant temperature ºC ( ºF).
Coolant radiates excess heat to the air.
Air flow is fan assisted.
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4. Liquid cooling (System Components)
Cooling fan-used to increase the airflow over the radiator when the vehicle is not moving. It may be driven electrically or mechanically.
Pressure cap-fitted to the top of the Radiator/ expansion tank, it controls the pressure in the system
The Water Jackets-passages in the engine which the coolant flows through removing heat from the engine components
Rubber Hoses-connect the engine to the radiator and heater, they allow for engine movement.
Heater-small radiator inside the car that the hot coolant flows through heating the cars interior
Water Pump-circulates the coolant around the system, driven by the engine
The liquid coolant- a mixture of water, which carries the heat away and anti-freeze which prevents the water from freezing and damaging the engine, anti-freeze can also reduce corrosion, helping to prevent the system becoming blocked, as the coolant warms up with engine temperature, it expands pressuring the system. The pressure/radiator cap must never be removed while the engine is hot
Radiator- fitted in the air stream, it allows the hot coolant to be cooled by passing the heat off into the air stream by convection
Thermostat-allows the engine to warm up quickly and regulates engine temperature.

5. Air Cooled
Water Cooled
Water Jackets
Cooling Fins

6. Downflow Radiators Tanks are on top and bottom.
Coolant flows down through core tubes.
Core
tubes
Coolant flows out of bottom tank back to engine.
Automatic transmission oil coolers are at bottom.
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7. Crossflow Radiators Tanks are on sides. Allows lower bonnet line.
Core tubes run horizontally.
Transmission oil cooler may be positioned in side tank.
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8. Antifreeze Normal temperature range for water to remain liquid.
Boiling
Increases under pressure.
Ethylene Glycol additive to lower freezing point.
Advantages of antifreeze:
Prevents winter freezing.
Freezing
Resists rust and corrosion.
Lubricates water pump.
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9. To top hose and radiator
Thermostat
To top hose and radiator
When cold - thermostat closed.
Route to radiator cut off.
Bypass allows coolant to circulate around engine.
When hot - wax-filled pellet expands and opens thermostat.
Coolant allowed to flow to radiator and by-pass port is blocked.
By-pass port
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10. The operation of the Thermostat

11. Water Pump Drive pulley Leak bore Main shaft Seal Bearings Impeller
Water pump housing
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12. Rubber Hoses- Carry Coolant And Allow For Engine Movement
Flexible hoses carry coolant between radiator, engine block and heater core.
Upper hose from the radiator is connected to the cylinder head.
Hoses carry coolant to passenger compartment heater.
Lower hose from radiator is connected to water pump.
Expansion tank keeps system topped up.
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13. Engine-Powered Fan
Main purpose is to generate air flow across radiator core tubes, when the vehicle is not moving
Bolts to water pump hub.
May have a spacer.
Fluid coupling and thermostatic clutches slip at given times.
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14. Temperature sending unit
Electric Cooling Fan
Thermostat switch
Temperature sending unit
Uses DC motor and thermostat switch.
Low temperature:
Low temperature indication.
Thermostat switch open.
High temperature:
High temperature indication.
Thermostat switch closed.
Current feeds fan motor.
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15. Radiator Cap Pressurizes system and raises boiling point.
Pressure valve opens when coolant overheats.
Excess coolant released to expansion tank.
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16. Closed Cooling System
When engine is hot, excess coolant flows to expansion tank reservoir.
When engine cools, vacuum valve opens to allow coolant back to radiator top tank.
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17. The Air Cooling System
Advantages-system is simpler and lighter in weight (less parts), no coolant leaks, works in all climates.
Disadvantages-Greater engine noise due to no water jackets, not suitable for in-line engines due to heat build up, cooling fan absorbs or uses a significant amount of engine power, car interior heating difficult to arrange

18. Safety Precautions and Servicing of the Cooling System