M30 Overheating Problem Diagnostics

Ever since changing coolant this year I have been experiencing overheating. I suspeceted the obvious and ever since have , bled, bled, bled, bled, bled, and re-bled the system, all to no avail. Just checked it again and there really doesn't appear to be any air in the system.

Now I';m beginning to suspect the fan clutch, but when I test it cold, it spins with slight resistance.

Here is my first question - With the engine hot (but turned off) should there be noticeably more resistance spinning the fan by hand? It seems to have about the same "slight" resistance hot or cold. Plus, while the engine was running, I watched the fan as I increased RPM's and I didn't see or feel any additional air flow under the hood. I would assume the fan should have increased air flow as I increased RPM's - Right?

Thanks in advance for your help and advise.

MB

Fan clutch fan should blow alot of air around after the engine is fully warmed up. If you switch engine off when it is hot, that fan generally should come to an abrupt stop, if not, it is freewheeling and likely bad clutch.

It does sound like fan clutch is bad.

Anybody have the ETK part number for a 1990 535i 5-speed radiator fan clutch?

(I haven't been having much luck with BMA without having the exact part# on hand when I order)

MB,
I ordered mine through BMA on line, no problems. The ordering process guides you according to the year and model car you have, then ends up with the part #
Good luck. Getting the fan clutch off can be tricky.

Its an easy test. If the car doesn't overheat when you are moving then chances are that its airflow related. You can also jump the wires to the aux fan switch that is screwed into the radiator. That electric fan should provide enough airflow this time of year to help diagnose the cooling system.

Didn't see a fan clutch for mine (at least at first glance) online. I'll check online again or call Patrick tomorrow.