Sealing the thermostat housing...

[COBALT]

Back when I had a cast-iron intake that was filthy dirty and didn't want to seal at the thermostat housing I came across Fel-Pro's reusable thermostat housing gasket:

Updated linkhttp://www.federalmogul.com/en/After...mostatGaskets/

Instead of messing around with sealants, and paper gaskets this thing is installed dry. Just clean off your mating surfaces on your housing and your intake with some brake cleaner and a scrubbing pad like scotch-brite, until it's squeaky clean and dry to the touch. Install this thing, and snug the bolts down by hand (don't torque). This gasket protects a bit from overtightening, but it doesn't have to be all that tight to begin with.

It should seal like a charm. Best part is you can take it off later, clean it off, and re-use it.

I have two of them (one i had to modify when a bolt hole had been retapped in an old intake), but the one I use now I've reinstalled 3 times with no problems.