I just replaced the head gasket in my '92 535i. With 258,000 miles, it was due for some major maintenance. I had the head resurfaced and replaced the cam and rockers as they were worn. I used an MLS gasket at .051 thick with some gasket sealer and ARP head studs to hold it together.

So now I have a mystery cooling system problem.

I put the engine back together and the only extra parts I had were the ones I deliberately left out (the injector electrical connector clips).

I refilled the cooling system by leaving the bleeder open, filling the reservoir until coolant came out the bleeder, then closing the bleeder and continuing to fill the reservoir until it wouldn't take any more.

I turned the heat on and started the car. It warmed up and the needle stayed at the middle mark for "a little while", but I wasn't getting any heat. Then in a period of about 10 seconds the needle went up to the red mark and I shut the car off. I left the key on and the temp was back to normal within a couple of minutes, but all subsequent attempts to run the car had the same result.

I was not getting heat from the vents. The radiator and the radiator hoses were cold, but the short hose from the thermostat housing to the waterpump was hot. I didn't hear the heater circulation pump and couldn't tell if the heater valves were operating. I replaced the heater valves a couple of months ago and had heat until I had to replace the head gasket (although the system was a bit flaky and would sometimes "forget" that I had the heat on until I moved the temp dial again.). I've heard the heater circulation pump run before, but don't hear it now, so I suspect it's not running. I have not yet probed the electrical connectors for voltage to see if the valves and pump are energized.

Due to the temp gauge's rapid return to normal once the engine is shut down, I believe I'm getting an air bubble in the thermostat, BUT bleeding doesn't give me anything but coolant. At first I thought it was a bad thermostat, but I replaced the thermostat and the problem persisted. I put the first thermostat in a pan of boiling water on the stove and it operated.

The system *should* function properly when completely stock (which it is, except for the MLS head gasket).

So...

How hard are E34/M30 cooling systems to bleed, normally?
Is the best bleeding procedure just to bleed it, or does it need to purge via multiple thermal cycles?
Can an empty heater circuit cause the behavior I described?
Do the heater valves make noise when they operate?
Has anyone ever tried "hot wiring" the heater valves and pump?
Has anyone had good results drilling a vent hole through the thermostat?