Engine cooling system device (BMW 3 Series E46)

Cooling circuit diagram

Elements of the cooling system

The engine is equipped with a circulation cooling system. Until the engine is warmed up, the coolant circulates only in the cylinder head and block and, with the heater tap open, in the heat exchanger of the interior heater. As the coolant temperature increases, the thermostat opens a large cooling circuit. The coolant is directed through the radiator by a constantly running pump. There is an innovation in gasoline engines, which consists of the so-called cooling by characteristics. In this case, the engine management system regulates the opening temperature of the thermostat and thus optimizes the engine temperature according to the fuel consumption criterion.



The coolant is poured through an expansion tank, which is located on the side of the radiator and serves as a container for the liquid. It compensates for the expansion of the liquid that occurs due to its heating and allows it to decrease in volume after the engine cools down.

To improve cooling efficiency, the system is equipped with a temperature-controlled fan. When the coolant temperature rises to +93°C, the thermal switch turns on the fan via a relay. If the coolant temperature drops below +89°C, the thermal switch turns off the fan again.

The radiator fan may turn on when the engine is not running. Due to the presence of heat stagnation in the engine compartment, this can happen many times. Therefore, when performing work in the fan area, wait until the engine cools down.

320i, 323i, 328i with air conditioning: To increase the cooling efficiency, an additional impeller is installed on the coolant pump shaft. A viscous coupling is located in the hub. As soon as the air coming from the radiator reaches a temperature of +90°C, a bimetallic plate in the viscous coupling connects the fan. The fan rotates at engine speed and provides the required air flow until the cooling air temperature drops to +60°C. After this, the viscous coupling switches off and reduces the fan speed. Due to the fan not working constantly, the useful engine power increases and fuel consumption decreases.