I had to use gasket sealant for the 1998 360 thermostat. There is a bead (or impression) that travels 7/8'sd around the housing next to one of the bolt holes. If you don't seal the gasket it will leak at that point every time. I don't know if it would make any difference if it was a rubber type gasket or cork type.

 

Im in Wyotech technical school right now to be a diesel tech and we had a rep from permatex come in and explain about his stuff... he said to use permatex black for almost everything or gray is for high temp... it is used instead of a paper gasket and will work better than a physical gasket if the two mating surfaces arent perfect... DO NOT use blue silicone. It has an acid in it that can eat at the metal and mess stuff up when it gets into components.. it is old technology and the only reason they still sell it is because too many people still buy it... the military uses black and grey on everything they use and it holds up very well... follow the directions on the back and dont put too much on so it squishes out everywhere.

 

Thanks fellas for the input. I didn't use any Permatex on the thermostat or the water pump simply because the Sevice Manual didn't mention it. This decision was based primarily on a previous experience I had on a 2000 Town and Country I used to own. The Service Manual for the T/C specifically mentioned NOT to use a sealer on the timing change cover gasket.

I noticed an impression on the bottom of the thermostat housing after I used a small 1/4" angle grinder and 2" 3M Roloc disk to remove the old gasket.(this is simply one of the greatest inventions known to mankind) Can't figure out why that would be made that way, but some Permatex probably shoulda been used there.

So far no leaks after about two hours of driving. I guess we will see.

 

I use it myself and here is how I use the colors.

The gray- Applied to any engine component for its high heat resistance.
The black- Applied every where else on the truck. Mainly diff covers.
The blue- Stock tanks.

I have, and will never use it on a Transmission pan. Not in a million years. Doesn't matter what color it is.

 

+1 on the trans pan and permatex also makes this red spray stuff for cork gaskets and your supposed to spray it completely and let it sit till it gets tacky and you can just stick it it the pan and it stays there and doesnt move around as much