u/Alexx12x

I have a strange problem with my ventilation. I'm using Auto mode only and set the temp to be comfortable for me. No issues EXCEPT, when i shut off the engine for a break. After restarting now i only get warm, sometimes even very hot air. When turning down the temp, it blows more air (in the attempt to cool down) but air stays hot. Only way is to off ventilation completely and open the windows instead. Using manual mode for air distribution doesn't help either.

I'm unsure about the exact timeframe, but this only occurs when doing rather short breaks between starting the engine. I had a 5 hour trip on the german autobahn and did a break after 3 hours. No issues until after the break. The remaining time my ventilation only blew warm air. It also seems like this issue doesn't resolve itself after some more time. Had this for the remaining two hours.

No problems with overheating of engine or whatever, and if I wouldn't shut off the engine, everything would work as expected.

I've read numerous stuff about thermostat, water valve and so on but i rarely read about my exact issue. I guess i found something in a german z4 forum (so maybe not an exclusive E60 problem), but i can't recall right now. It feels like vents are suddenly sucking all the air from the engine bay. Is that even possible? Are there some kind of flaps that could be stuck?

Any ideas what causes this specific, reproduceable problem?

Thanks!!

Edit:

Engine is the M54B22 so 520i model. I think the thread from that forum was also a Z4 with the M54 engine.