'85 525 puked through radiator cap.

[Gene in NC]

'89 525 w 170k - gasket on the "heater" on the side of the throttle body failed with pinhole leak spouting coolant. Couldn't have been driven far. Wife drove 3 miles, car sat for about 45 minutes. Two miles into return the gauge jumped to red, and she stopped. I arrived within five minutes to see leak still spouting.

Replaced gasket and had what seemed like trouble bleeding. Compression test good.

Test drive of 2 mile residential loop was OK. Next day drove 2 miiles under similar conditions, watching temp gauge come up to and run at perfect mid point. Stopped and maybe listened to radio for couple of minutes. Can't recall for certain. by time I could get out of the car it was puking through the radiator cap. After cool down refilled and bled. Perfect gauge readings on two mile drive home. While stopping in street to back into drive
it started to lose coolant again.

Rad cap is original.

[whiskychaser]

Cant speak for the 89 but there was a recall for the rad cap on mine. Worth asking if BMW will give you one for free?. The heater on full, fast idle and open the rad vent procedure should bleed it. If not turn it off and let it cool a bit and you will be able to add some more coolant. I will bet you can put more in today

[Ross]

A lack of circulation could allow for a normal gauge reading while overheating as could air in the system. Either uncirculated less hot coolant or no coolant in contact with the gauge sensor.
If the gauge is correct the puking could be from over pressure rather than an actual overheating, IE headgasket failure allowing combustion gas into the cooling system.

I don't think M20s had the plastic impellor water pumps so circulation is probably not an issue.
Bleed it and cross your fingers.

[Gene in NC]

Thanks, Ross. Fan clutch was bad. Replacement seems to have fixed problem. Keeping fingers crossed. Sure looked like head gasket, esp with other indications.