1985 300SD thermostat housing leaking
 

Pulled the thermostat the other day, account I thought it stuck,
but it was just low on antifreeze. Put it back together and it was leaking. I didn't see any gasket, when I took it apart. So took it apart again and applied a little blue sealant. Its seems to have stopped the leak. Is that normal to apply a little sealant???? Or should I have used something else?????? Thanks in advance....

I think there should be a gasket....
 

I have a 123, but I'm fairly sure there should be a gasket. They come with the thermostats but there are 2 kinds. One goes around the outside of the thermostat, and the other fits on one of the inner surfaces. You need either one or the other.

Blue Stuff, if it is silicone, is real bad for the cooling system according to some posters here. I'm a newbie, but I just did my first coolant flush. When I got my thermostat they gave me the wrong gasket the first time.

When doing a job like that I always use a gasket and a little blue stuff for good measure.

nikodem60,

I only use a sealant when the surfaces that form the joint are pitted or corroded and do not clean up with a fine abrasive. I still use a new gasket though and only count on the sealant to fill in the uneven surfaces under the gasket.

Pitting and other signs of corrosion are an indication of an incompatible sealant having been applied, or too infrequent changes of coolant. Most manufacturers select gasket materials to be compatible with the various base materials of parts, and the coolant chemistry to avoid typical corrosion problems. Arbitrarily changing these can increase the likelihood of a corrosion event significantly. In the case of the thermostat housing, I believe the gasket design is intended to isolate the galvanized steel thermostat support ring from the aluminum housing, as that is what was intended for the 1982 240D we have. Other models will be slightly different and newer ones have plastic housings or housing covers to further minimize the corrosion potential.

Good luck and I hope this helps, Jim