How cooling works
About 6.5 liters of coolant is constantly pumped through the engine. This work is done by the water pump. It is driven by a V-belt; the coolant flow is pumped by a small paddle wheel.
It depends on the temperature of the coolant: which way it will flow through the numerous channels and hoses.
If the engine is cold, not warm. then the coolant flows "small circulation circuit", which passes through the engine, the radiator of the heating system, and also through the oil cooler (only in a car with a turbo engine or automatic transmission).
Starting from a certain temperature, the thermostat opens "large circulation circuit", which also includes a radiator for the cooling system. If the coolant temperature rises even higher, then the radiator electric fan starts to work, it creates additional cooling.
Pressurized cooling system
At operating temperature, there is an excess pressure of 1.2-1.35 bar in the cooling system (for models manufactured before July 1979, the overpressure is 0.9-1.15 bar), which contributes to an increase in the boiling point to a value greater than 100 degrees Celsius.
Therefore, the engine can reach operating temperatures greater than 100 degrees Celsius without the fear that the coolant will boil.
To maintain pressure in the system, the plug of the expansion tank is used, it has a safety and vacuum valves. The latter lets in air when the coolant becomes colder and occupies a smaller volume.
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