The cooling system circuit is controlled by a thermostat. When the engine is cold, the coolant circulates only in the cylinder block and in the heater radiator. When the coolant warms up, the thermostat opens, and the coolant is pumped by a water pump, which is driven by a poly-V belt in a gasoline engine, and by a toothed camshaft drive belt in a diesel engine. The coolant passes through an aluminum radiator and is cooled there by the oncoming air flow.
At high coolant temperatures, additional cooling is provided by an electric fan. When the coolant temperature slightly exceeds +100°C, the engine control unit switches on the fan via a relay. When the coolant temperature drops, the fan switches off.
The expansion tank serves as a reserve container for the coolant - it receives the coolant that expands when heated and returns it back to the cooling system circuit when cooled. The coolant is added through the expansion tank.
Precautions: Before working in the engine compartment, turn off the ignition. The fan may turn on spontaneously when the engine cools down, which is dangerous! In this regard, you need to be careful when working with the radiator and fan.
Cooling system diagram
1. Heater radiator; 2. Engine; 3. Thermostat housing; 4. Water pump; 5. Coolant expansion tank; 6. Expansion tank cover; 7. Radiator; 8. Bypass hose; 9. Oil radiator.