Ok. I bought a tube of the permatex grey RTV sealant. It says it can handle temps up to 652 degrees F. It also says it dries in 1 hour, and then cures in 24 hours. I plan on using this for the thermostat housing and oil pan gaskets. Do I have to let the car sit for 24 hours after I put everything back together?

 

it's a good idea to let it set up fully but you probably will have no problems running the engine after an hour.

 

If you are in a hurry then the stuff that works great is called:

Permatex Rightstuff http://www.permatex.com/right_stuff/right_stuff1.asp

It sets in five minutes and allows immediate use of your vehicle. My 91 Vert is the third car I have used this stuff on and I am very impressed! I've used it on oil pans, front covers, valve covers, and thermostat housings with no problem. I've used the grey and blue stuff before and had several instances when I had leaks and had to redo the gasket.

Oh, even though it can't handle the same high temps as the grey stuff, it is plenty heat resistant enough for your desired use.

 

As stated it will work. I have to suggest to just get the gaskets. The thermostat gasket is only $1 at any auto parts store. It will save you the time of setting and any hassle if it has to come off. The hassle of scraping it with a razor blade and cleaning it with brake cleaner. The oil pan I can understand that gasket is $30 and the pan rarely comes off but is always a good idea to use the appropriate gasket if possible. RTV works great where a gasket doesn’t if your surface is buggered up.