BMW E36 cooling system bleeding and coolant loss

1. Fill with coolant on a cold engine and open the bleed screw on the neck (a large black plastic cross-head screw next to the filler cap). 2. Pour coolant slowly into the expansion tank until no more air comes out of the screw. 3. Close the screw and the cap, start the engine and hold the revs slightly raised until the thermostat opens. 4. Squeeze the hoses and add coolant if needed. It is a good idea to keep the heater on hot.

When cold, the level should be at the Kalt mark, not filled to the brim. When warm, the level rises about 5 cm in the tank. If the level rises to full and the hoses swell, the cause is usually a faulty cap or one that opens at too low a pressure.

Common causes are the heater core O-rings, the expansion tank sealing rings or a crack in it, a crack in the plastic part of the neck, the water pump O-ring, a faulty expansion tank cap and the head gasket. The leak can be located by pressure testing the system at 1.2-1.5 bar.

An air lock blocks the coolant circulation: the car does not warm up and the heater blows cold. Raising the front of the car helps the air out. If bleeding does not fix it, the cause may be a stuck thermostat or water pump.