Bleeding cooling system
My daughter has a 1999 BMW 318i SE manual. I recently replaced the expansion chamber, but, try as I may, I cannot get the heater to blow hot air. My efforts to date include filling the large hose running from the engine to the expansion chamber while the hose was raised above the engine and when it was absolutely full, connecting it up to the expansion chamber, running the engine and opening the bleed screw in the hose to expel air until only coolant is coming out. I have repeated this several times, but all my efforts have been without success. George Woodward The system should be bled out as completely as possible with the engine cold and without the engine running. Very often, attempting to open the bleed screw while the engine is running can drag in more air.
Once the system has been bled through as fully as possible, then the bleed screw should be tightened up and the heater set to its maximum temperature with the heater fan set to slow. The advice from BMW is to then run the engine with the coolant cap removed and give the engine three or four bursts of acceleration. They also advise not to run the engine for more than 30 seconds as once the coolant gets warm it will expand.
After refitting the coolant cap, give the vehicle a run to get the cooling system up to temperature. Hopefully, at this stage, the heater will be blowing warm air, but if this is not the case, allow the engine to cool down before removing the coolant cap and repeating the process.