Cooling circuit diagram
1 - radiator
2 - expansion tank
3 - interior heating
4 - thermostat
5 - coolant pump
6 - cylinder block
7 - return
8 - feed
9 - throttle heating
10— heater valve
Elements of the cooling system
1 - radiator
2 - lower radiator hose
3 - upper radiator hose
4 - radiator cap
5 - water pump
6 - thermostat
7 - thermostat housing
8 - radiator fan impeller
9 - viscous coupling
The engine is equipped with a circulation cooling system. While the engine is not warmed up, the coolant circulates only in the head and cylinder block and, when the heater valve is open, in the passenger compartment heater heat exchanger. As the coolant temperature rises, the thermostat opens the large cooling circuit. The coolant is directed through the radiator by a constantly running pump. There is an innovation in gasoline engines, consisting in the so-called performance-based cooling. In this case, the engine management system regulates the thermostat opening temperature and thus optimizes the engine temperature according to the criterion of fuel consumption.
The coolant is poured through the expansion tank, which is located on the side of the radiator and serves as a reservoir 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 connects the fan through the relay. If the coolant temperature drops below +89°C, the thermal switch switches off the fan again.
The radiator fan may come on when the engine is not running. Due to the presence of thermal stagnation in the engine compartment, this can happen repeatedly. Therefore, when working around the fan, wait until the engine has cooled down.
320i, 323i, 328i with A/C: 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, the bimetallic plate in the viscous coupling turns on the fan. The fan rotates with engine speed and provides the required air flow until the temperature of the cooling air drops to +60°C. After that, the viscous coupling turns off and reduces the fan speed. Due to the intermittent operation of the fan, the useful power of the engine is increased and fuel consumption is reduced.