I just finally got my exhaust bolts today from "Fastenal", and I found some loctite called "Loctite 242" which claims to lock threaded nuts in place to prevent loosening over time, while still allowing the nut to be removed again in the future with standard tools. Is this ok to use for exhaust bolts?

 

Loctite 242 is the medium strength threadlocker. It would be fine with exhaust bolts, even though it loses most of its thread-locking ability at temperatures above 250F or so. It will still provide some anti-loosening, while keeping the threads from rusting as much as they would without it.