[KTL]

Use heat, but let it cool. The nut and thermo. housing are different metals. The thermo. is aluminum and expands more when heated. Soft aluminum and tight fit can equal galled threads! Make sure to clean all the crud off the connection at the thermo. Not just near the threads, but on the back side of the nut at the oil line itself. It can bind here too. Use a good penetrant like Wurth, PB B'laster, Kroil, etc. Don't trust Liquid Wrench alone!

The line that changes from rubber to metal and winds around the rear (crank pulley side) of the engine can be rough. That connection gets a little crusty. A couple of snug crescent wrenches, your baby sledge, penetrant pre-treatment, and some good whacks will get you home. A helper is good to have for this crusty connection. Preferably not female. No offense, but they don't take kindly to having hammers swung near their hands and sometimes can't counterhold worth a crap.

Not too hard to do physically, but pretty hard on the wallet.