Hello, I have a 91 M5 that has a overheat problem. I have had the thermostat and fan clutch replaced and the temp guage is within range however the coolant is still getting super hot and is boiling over. I cannot find a leak. I am hoping someone might be able to help me out here.
You might have a head gasket leaking...any oil in coolant (or coolant in oil)? There is a reasonably active forum for the E34 M5 on www.m5board.com, go to the E34 section.
are you sure there's no air in the system? There's a bleed valve at the back of the engine compartment, by the heater valves. Open that with the engine idling to see if any air comes out. An air lock can cause what you're experiencing.
I quick and inexpensive thing to try is replacing the coolant cap. They have a pressure valve in them and they can fail. Causing the coolant to "Boil" over at normal temps.
