thermostat housing gasket - silicon or no?

[FWinNH]

I don't know when they started producing m50's for 525's, but I'm positive I have a M50.

OK, you're right (of course - it's your car) The last of the M20's was produced in August 1990. So I assume that yours was built post September '90.

And sure enough yours does apparently have a paper gasket rather than the profile gasket (also shown in the below drawing). I would definitely use some permagasket compound or something similar.

http://www.realoem.com/bmw/showparts...03&hg=11&fg=35

[632 Regal]

Bill R like Hylomar.

[Dave M]

Bill R like Hylomar.

I'm through half a tube of the $hit putting my car back together (none on the head gasket )

Dave M

[calmloki]

After doing the waterpump and thermostat housing replacement on my M50 '93 525iT I would (and did) go with no goop at all. The M50 is all compressible rubber rings. Just clean mating surfaces well. Not leaking yet...
Tom

[Derek A.]

I thin coat of RTV on the metal not sealing surfaces will help to prevent leaks down the road, especially of there is pitting present on the aluminum.

The real early M50's used a paper gasket. After that its all profile gaskets and o rings.

[Kalevera]

No RTV. Many an engine is destroyed by some idiot goobering it up with the stuff. It has its uses, but the tstat cover is not one of them. Use a scotch brite pad or a new razor blade to clean the aluminum, the rubber profile gasket and tstat O ring prevent leaking, but things need to be flush.

These engines only need a TINY dot of RTV at gasket junctions between covers (ie - pan/block/lower timing cover gets a dot on each side on the outboard side of the gasket during a pan gasket job). For some reason, people think that RTV can universally replace the use of an actual gasket. To make matters worse, they put more than a dot on the motor to form some kind of seal that won't leak, and neglect the fact that just as much squeezes in as what squeezes out. The stuff solidifies and turns into strings of goob, which proceed to clog tiny and necessary coolant passages, overheating the car and trashing the head. Or it can get in the oil (pan gasket scenario) and lunch the bottom end.

So, no RTV. And I doubt you'll need hylomar in this situation, either. Clean, bolt, and go. If you still have leaks, then there's a pitted or damaged surface that merits replacement, anyway.

best, whit