98 528i overheating and hot air goes hot and cold.

[jeffbeck]

I just started having this problem, I read up on past posts and found similar symptons, but here's what's going on with mine.
I'm in NY and outside temp is in the 40's and lower. The thermostat is pinned within 10 minutes of local driving. Once the car get's moving steady again the temp goes back down to 1/2 way.When the temp is pinned the hot air will sometimes go cold, and then hot again. Once the car is moving steady and the temp goes back to 1/2 the hot air will come back and it will be blowing hotter than normal to the point that I can hardly hold my hand in front of it for very long. At the same time when it is blowing hot It only blows hot on the driver side and not the pass side. Any thoughts? The Fan seems to be fine, although I haven't seen the auxilary fan go on much, but then that might be normal. My brother has a 97 528i and had a similar problem that turned out to be the water pump.

Before I take it to BMW and spend $$$ I was wondering if anybody had any thoughts.

Leo

[zedster7]

I dont know if this will work but I had a similar problem that was caused by lower fluid levels (anti freeze+water) in the radiator. I know mine is a sealed system but check the reservoir under the bonnet (Thats the hood to our fine American friends). It would be a shame to spend £$£$£$ for a few litres/pints of water and an convoluted explanation from the BMW Service manager.

[sagbels]

I think your coolant system needs bled. I just went through the same thing with my '97; I replaced the fan clutch, aux. fan switch and the thermostat. I think the only problem was air in the system. This was hard for me to accept because the system hadn't been opened for anything prior to the problem (the air pocket must have been hiding in a spot where it wasn't causing any problems).

Top off your coolant, re-install the rad. cap and start the car. Then crack-open the bleeder screws on top of the rad. and the thermostat housing while the car is heating up to let the air out. Stop bleeding when nothing but coolant is coming out. Be careful not to overtighten the screws - everything is plastic!.

Good luck.

[jeffbeck]

it was the water pump

[russiankid]

air lock in the heater pipes or core

[russiankid]

and i dont think there is a radiator cap, there is a bleeder screw on the thermostat housing, and a cap on the coolant tank