Small and large circle of coolant circulation
In order for the engine to warm up to operating temperature faster, the cooling system is divided into a small and large coolant circulation circle.
- After starting a cold engine, the coolant circulates in a small circuit: from the coolant pump to the engine body, as well as to the cylinder head and back to the coolant pump. In the small circuit, the coolant also passes through the heating heat exchanger.
- When the coolant reaches the required temperature, the radiator turns on during the cooling process.
- The thermostat turns on the radiator. It opens the connecting hose between the engine and the radiator so that the cold coolant from the radiator mixes with the already heated one from the small circuit.
- By gradually mixing hot and cold coolant, a sharp temperature drop in the engine body can be avoided. Cold water flowing down forces hot coolant up into the radiator. There it is cooled by the radiator fins. The small circulation circle is closed at the same time as the radiator is turned on.
- The functions of the switch in the thermostat are performed by a special solid heat-sensitive filler, which is located between the walls of the glass in which the valve plate is fixed. When the coolant is heated, the heat-sensitive filler melts and expands, due to which the valve opens.
Thermostat operating principle
- As the coolant temperature increases, the thermostat increasingly opens the passage for cold coolant to flow from the radiator and simultaneously closes the small circulation circle.
- If the coolant temperature drops below operating temperature while driving, a spring in the thermostat presses on the valve plate, returns it to its original position and closes off access to the radiator until the coolant warms up again. The thermostat is located when looking in the direction of travel:
- On 1.4 liter engine (engine type "C") in front of the coolant pump in the upper radiator hose;
- On 1.7-/1.8-liter and 16-valve engines below the ignition distributor;
- On a diesel engine, below the brake booster vacuum pump.