Loosen the bleed screw at the top of the radiator next to the expansion tank and wait until the coolant stops flowing out with bubbles.
Loosen the bleed screw (arrow) on the coolant tube in the oil filter area until no more coolant comes out with bubbles.
Tighten the bleed bolts and add coolant to the expansion tank.
Diesel engine: Air is removed automatically through the top tube to a separate expansion tank, there are no air removal bolts.
Close the expansion tank with the cap. The engine must not be warmed up with the cap open, as this may cause damage.
Start the engine, set the heater to the WARM position and warm up the engine. Maintain the engine speed by applying the gas at 2500 rpm. Removing residual air from the system will reduce the coolant level to the MAX mark on the tank.
Turn off the ignition.
Caution: Wait until the engine has cooled down, otherwise you may get burned by hot steam or coolant when opening the expansion tank cap.
Add coolant to a cold engine up to the MAX mark on the expansion tank.
Loosen the bleed bolts again and make sure that the coolant comes out without any air bubbles, then tighten the bolts.
Check the cooling system for tightness, especially the hose connections, drain plugs and water pump.
[The article was copied from an online resource: bmwman.ru]