Bolt Snapped - Sealant?
 

My upper thermostat housing bolt snapped off in the hole and I can't seem to get it out.

(same problem as http://www.toyota-supra.info/forums/...ead.php?t=6233)

Are there any sealants that can withstand coolant pressure that I could use to seal the thermostat on with one bolt below it?

Nope, no sealant will seal the thermostat housing, it needs the 2 bolts. You will need to drill it out, then tap it and helicoil it. The size of the bolt you snapped off is M6 X 1.5, meaning the diameter of the threaded part of the bolt is 6mm in diameter. So you have to use a 6mm drill bit, then go buy an M6 helicoil kit. Center punch the direct center of the bolt before you drill, you MUST be dead center when drilling or the housing wont line up when you are done. You might want to have a shop do it.

Or you can get a new water outlet housing from a junkyard or dealer. Won't be cheap from Toyota. The water outlet housing is the part that the bolt snapped into and is held on by 2 nuts and 1 bolt, to the left of the CPS or distributor.

Must Disagree
 

I also had the lower bolt of my thermostat housing break, but with a good sealant and the upper bolt tightened down, it held for about five months till I got to fix it. It never once leaked. I drained the cooland level down below the housing and let the sealant sit overnight to dry. Also, its not easy to get the broken bolt out, you have the fan shroud in the way and the radiator, most drills will not fit, so you have to disasemble a lot to get to it. I do feel much better with both bolts in place though.

Scruffboy

I used some red RTV as a gasket and it's sealed pretty tight with only the lower bolt.