BMW: No Heat on inside of car, coolant level, radiator fluid

Question
Hi Josh,
My question to you is in regards to my 97 528i. The problem I seem to be having is that I have no heat in the cabin of my car. The first thing I suspected was the Thermostat. Then I remembered that I had drained the radiator fluid when but did not bleed the system for air. Could this be a cause of why I don't have any cabin heat? I forgot to mention if the car sits at idle for a while it will warm up getting to the halfway point on the temp gauge. When I start driving the temp gauge will go back down to just above the cold mark. Thank you! Any help is greatly appreciated.

Lawrence

Answer
Lawrence.  It is most likely the problem.  See, inside the cabin is a little "radiator" called the heater core.  The engine warms up coolant and when you turn the knob to heat the air inside, coolant flows through this little radiator.  Outside air flows across this radiator and blows heat onto you.  When you drain the coolant system you also drain the heatercore.   Most people forget about this. When you fill the coolant back up, a large air bubble is trapped in the heater core.  When you turn on the heat inside, that air bubble goes out and into the engine.  I would check your coolant level immediately and bleed the system.
 When bleeding the system, turn the heat on full-blast (high temp) while you let air escape from the bleeder screw.  
 Good luck,
 Josh