BMW E34 cooling system bleeding and expansion tank
How do I bleed the BMW E34 cooling system?
1. Raise the front of the car and open the expansion tank cap. 2. Fill with coolant, start the engine and set the heater fan to full. 3. Open the bleed screw and let the revs rise. 4. Add coolant as the level drops, and continue until no more air bubbles come out. 5. Close the bleed screw. Bleeding can take hours.
How can I tell there is air in the cooling system?
The temperature gauge rises at idle, heat comes only when driving or coolant bubbles out of the expansion tank. While bleeding, the temperature gauge swings until the air has gone. The cap can also let air through: it should not, and in that case it is replaced.
The expansion tank or cap leaks - what should I do?
The O-rings at the top and bottom of the expansion tank leak over time, and replacing them has often stopped the leak. Also check the hose clamps. The cap pressure is 1.4 bar. When replacing the radiator, it is worth replacing the cap too.
Why does the check control warn of low coolant although there is coolant?
The level sensor is at the bottom of the expansion tank. Its connector may be unplugged or the sensor may be stuck, oxidised or in the wrong position. Check the connector and the sensor before suspecting anything else.