ORIGINAL: airbusdrvr
I would think that tighening the muffler bolts when the engine is hot would be my last choice. Use the Blue Loctite when the engine is at room temperature. As the the engine heats after start, the aluminum will expand to a greater degree than the steel bolt causing a more snug fit between the cylinder/muffler and the steel bolt.
I'm guessing that the reason it works so well would be due to two things.
You do the tightening after stopping the engine and aluminum cools quite a bit faster than steel. A bolt that's almost completely encased with no contact with the air certainly won't be cooling very fast. Second reason is like everything in our hobby, there is a technique to be learned/used. Gotta learn how strongly we need to tighten the suckers without stripping them.
About technique.......... The through bolt on lots of mufflers are often a problem. The technique with them is most certainly something many have to learn. Many guys don't realize the bolt threads through the endcap. It's very important to tighten that adequately before tightening the nut that's present. The nut is actually a lock nut, yet many think it's the primary holder. Just another detail to be learned by some in our hobby. (It seems appropriate to mention the muffler bolt because it's quite often the problem newbies have with loose bolts.)