Open the air release valve "arrow" on top of the radiator next to the expansion tank and keep it open until the liquid flows out without containing air bubbles.
Close the air bleed valve on the radiator.
Models 316i/318i: Additionally, open the air release valve "1" on the thermostat housing.
Close the air bleed valve on the thermostat housing.
Start the engine and push the gas pedal to rev up to 2500 rpm. The air remaining in the system causes the coolant level to drop to approximately the MAX mark on the expansion tank.
During the heating process, add liquid as needed and then close the lid.
After warming up the engine to operating temperature, leave it running at slightly increased idle speed (about 1200 rpm).
Open the air bleed valve again and leave it open until only coolant comes out.
Caution Rotating fan and V-belt. Risk of injury!
If necessary, add coolant up to the MAX mark on the expansion tank. Close the radiator cap.
Check the cooling system for leaks, especially at the hose connections, drain plugs and water pump.