What is the best way to seal a thermostat housing on a 225 slant six? I tried with a gasket and it leaked. I then tried with a gasket and gasket sealer and it leaked again! With the gasket and sealer, it seemed like the sealer just squeezed out when I tightened the housing bolts. Dumb question, but I'm stuck!

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"You know a car is really yours when you've touched every fastener on it." -David Freiburger

Make sure the head surface and housing surface don't have any major flaws to them. A gasket and light coating of sealer is all you should need - don't go crazy with the torque either. Make sure on assembly the housing is sitting flush to the head - I've seen some intake/exhaust gaskets run wide enough that it touches the housing gasket and doesn't allow it to seat flush.

Are you sure its leaking at the gasket and not the hose?

i had one where the lower bolt on the housing was leaking just a little
even though sealer was all around inside bolt hole.
also another one was housing had a small crack near bolt hole flange.
I finally used another sealer Permatex non hardening thread sealer and
that sealed the leak.

I have a sanding board to redress the aluminum housing and use Permatex Ultra Black on both sides of a blue Fel-Pro gasket. Just snug it down and let it cure over night.
The next day you can fill it with anti-freeze and run it.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

There is a water pump/thermostat housing silicone from Permatex that works very well. Its gray and comes in a small gray tube. Is your housing aluminum? Try to find a cast iron housing...aluminum ones suck. Otherwise do as Ted suggested and scrap the sealing surface on the head until you see shiny metal!

One thing to make sure of is that the thermostat doesn't slip out of its little indent in the thermostat housing and cause a gap between the housing and the head. I have been down that road many times.

Try putting the thermostat in the housing and laying the housing flat with the thermostat hole facing up. Now run a 1/4 inch bead of your favorite color Permatex gasket maker sealant around the perimeter of the thermostat and overlapping it onto the housing (I like red or orange, nice contrast with the engine). Walk away for about 30-45 minutes, long enough for the sealant to skin over and be strong enough to hold the thermostat in place. Now carefully place the housing onto the block and start threading the lower bolt into the hole get that about halfway in and then start the upper bolt. Now get the lower bolt mostly snug, then snug up the upper bolt, then finish tightening the lower bolt. Now fill and check for leaks.

If your thermostat housing is a replacement, it could be the problem. The last one I got from AutoZone (Mexican made Factory Air brand, I think) wasn't made very well and I had to Dremel-tool out the recess to get the thermostat to sit deep enough to let everything sit right.