About a year ago I did some testing on various materials used for sealers, and posted the results in a thread. Someone recently recommended it should be a tech article, so here it is.
I ran some tests to see what happens to different materials under extreme heat. I tested copper spray, high-temp RTV, and Super Tech (Wal-Mart) axle grease. I'd heard of using grease before, but found it hard to believe and wanted to find out.
I took a SS turbo gasket, and applied a light coat of each to different areas and let them set for 30 minutes or so. I then heated up the back side to almost red hot, let it cool, and then repeated this 2 more times.
The results were somewhat surprising. The RTV immediately turned to white powder and basically burned completely away. The copper spray powdered and flaked, but sort of stayed in place. The axle grease turned to a hard crusty looking material.
Here's where it gets interesting. After a shot of air and some wiping with a shop rag, the copper spray residue and what was left of the RTV were gone...completely (although there was some discoloration). But the axle grease didn't budge. Not only did it stay in place...it's still in place because I couldn't chip it all off evenly with a razor blade!
Here are some pics, followed by some mov files showing the process (I couldn't zap the background sound, so you may wanna lower your volume). The last pic is a bit blurry, but if you look closely you can see where I chipped at the grease a little and then realized I should take a pic first. And in the last movie, you'll notice that before I wiped it down, I hit the gasket with a shot of air.. and the RTV and copper spray residue just blows away.
Copper spray applied:
Ready for heat:
Here are links to the mov files:
One thing I'm not sure of is the effects of the grease on O2 sensors. And you don't want to use a lot of it, or get into a situation where pieces could come loose and damage things like turbine blades, etc.
Although the results are interesting, I'm not suggesting you should buy a bunch of stock in axle grease and start using it as a sealer for everything. For most situations, the RTV and copper spray should still be used as that is what they are designed for. But in those hi-heat cases where nothing seems to work, you may want to throw a little grease into the mix and see what happens.
Interesting, but sealant exposed to flame in open air has nothing to do with what goes on when it's used to seal two surfaces that are carrying away heat and which will never see red-hot levels (such as the sealing surfaces of an exhaust manifold and turbine housing).
If axle grease were a viable product for this mis-use, Barney Oldfield would probably not have gone to the trouble to develop Permatex.
For the record, the flame never actually contacted the materials. I held it on the back side below them, just enough to heat the metal.
Like I said, I'm not recommending that people start using axle grease as a sealer...but I've heard about this "old hot-rodders trick" and wanted to see if there could be anything to it.
The results were interesting though :)