The cooling system keeps the operating temperature between the limits of admissible temperatures (80 – 95 degrees Celsius).
Following the thermal process inside the cylinders, the component elements of the engine heat up beyond the admissible limits of the normal operation of the engine. For this reason the cooling system is necessary.
The cooling is an indirect one and is carried out with coolant, the system being with forced circulation, with pump. This system works at atmospheric pressure or under pressure (pressurized) at a pressure between 0.5 and 1.1 bar above the ambient pressure.
In the case of the pressurized system (with closed circuit), the coolant circulates under pressure in a closed circuit and does not come into contact with the atmosphere except through the valve of the expansion tank.
Coolant is also called antifreeze and is a liquid that contains glycols that prevent freezing, it is used to perform the heat exchange between the moving parts and the radiator.
The coolant ensures protection against freezing down to -35 °C.
Besides the heat transfer it performs, the antifreeze also has an anti-deposit role, thus avoiding the formation of limescale or other types that could significantly reduce heat transfer.
After long periods of use the coolant degrades and loses its properties.
For this reason, it is recommended to replace it regularly. The antifreeze must be replaced after a maximum of 3 years even if its concentration is appropriate.
The level of the antifreeze in the expansion tank must be checked periodically, it must be between the maximum and minimum limit.
The cooling system is composed of:
- the radiator: which is composed of two tanks, an upper one and a lower one, made of brass or steel sheet. The connection between them is made through several thin tubes provided with fins. The lower tank of the radiator is provided with a cold water outlet pipe, with a drain valve and with the fixing supports of the radiator;
- the water pump: ensures the forced circulation of the liquid in the cooling system. In the case of cars, the cooling pumps used are the centrifugal ones. The body of the pump is mounted on the engine block and communicates with the lower tank of the radiator and with the lower part of the cooling jacket.
To remember! The breaking or loosening of the drive belt of the water pump leads to the excessive increase of the thermal operating regime of the engine. In cars where the water pump, the alternator and the fan are driven by the same belt, its breaking will be announced by the lighting of the warning light in the dashboard of the motor vehicle which signals the operation of the alternator;
- the thermostat: is a double valve that automatically directs the circulation of the water in the cooling system, depending on the temperature regulating and keeping the temperature within normal limits of the water in the cooling system, thus ensuring the continuous operation of the engine. The optimal operating temperature of the engine which ensures maximum efficiency and minimum wear of the engine is between 90-95 degrees Celsius and is ensured by the closing and opening of the thermostat at the limit temperatures;
- the fan: can be driven by the crankshaft through a belt but it can also be driven electrically (electric fan). During the operation of the engine the fan draws cold air from the atmosphere and passes it between the radiator cells cooling the liquid;
- the thermocouple: is the part that is mounted on the radiator in the lower part of the inlet tank which is used to start the cooling electric motor. When the temperature of the coolant in the radiator reaches a certain preset level (87 degrees Celsius), the thermocouple closes the electric circuit that supplies the electric fan, thus putting it into operation.
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