General information and precautions (BMW 3 Series E46)

General information

The cooling system operates under excess pressure. It consists of a water pump, an aluminum radiator, a fan, and a thermostat.

The system works as follows. Cold liquid from the lower radiator tank enters through the lower hose to the water pump inlet, which pumps it through the cavities and channels of the block and cylinder head. After cooling the cylinders, combustion chamber surfaces, valve seats, the liquid enters the thermostat, which is initially closed. The liquid passes through the heater heat exchanger and returns to the pump through the cylinder block.

Until the engine is warmed up, the coolant circulates only through the block and cylinder head, as well as through the heater. When the liquid heats up to a certain temperature, the thermostat opens and the liquid enters the radiator through the upper hose. On some models, the thermostat opens and closes on command from the engine control unit. This system allows you to more accurately maintain the engine's operating temperature, the composition of the fuel-air mixture, and reduce the concentration of harmful emissions into the atmosphere. In the radiator, the liquid is cooled by the air flow passing through it when the car is moving. If necessary, the air flow is created by a fan. The cooled liquid drains into the lower tank of the radiator, from where it is sucked in again by the water pump and the cycle is repeated.

Depending on the model, the vehicle may be equipped with one of two types of fan. On models with a 4-cylinder engine and a 6-cylinder M54 engine, an electric fan is installed behind the radiator. On models with a 6-cylinder M52TU engine, the fan is driven by a belt from the crankshaft through a viscous coupling. The viscous coupling changes the fan speed depending on the engine temperature. At low temperatures, the coupling creates a small adhesion between the fan shaft and its drive, so that the fan rotates slowly. As the temperature rises, the coupling's adhesion increases and the fan begins to rotate faster. On these models, another electric fan is additionally installed in front of the radiator.



A description of the air conditioning system is given in paragraph 11.

Precautionary measures

Warning! Do not attempt to remove the expansion tank cap or disconnect any cooling system hoses while the engine is hot, as there is a high risk of burns. If the expansion tank cap needs to be removed before the engine and radiator have cooled completely (even if it is not recommended), it is necessary to first reduce the pressure in the cooling system. To avoid burning, cover the cap with a thick cloth and slowly unscrew it until a hissing sound appears. When the hissing stops, which means the pressure has dropped, slowly unscrew the tank cap all the way and remove it; if the hissing sounds are still heard, wait until they stop. In all cases, when opening the expansion tank cap, try to keep your distance from it and protect your hands.

Warning! Do not allow antifreeze to come into contact with your skin or painted surfaces of the car body. If this does happen, immediately wash away the spilled liquid with plenty of water. Never leave antifreeze in an open container or as a puddle on the garage floor. Children and pets may be attracted by the pleasant smell, but if ingested, antifreeze is fatal.

Caution: When working on models equipped with air conditioning, observe the additional precautions given in paragraph 11.