In layman's terms, yes. Chemically, that is not exactly true. Iron+oxygen= Iron Oxide. Rust is Iron Oxide + Water, which is technically called hydrated iron (III) oxide or Fe203xH20. Heating does two things - cooks out all the water, and turns the hydrated iron oxide which has bonded the nut and stud back into iron oxide, which has much lower shear strength. Also, if done correctly, the heat expands the nut more than the stud, which gives even more clearance. Sure, penetrating lube usually works, but you have to wait. I hate to wait. If you don't want to wait several hours, or a day, use a torch. The nut will come off right then.

 

I think they were speaking more about the y-pipe bolts not the actual manifold bolts when heating. At least I was, I'd never even attempt to get a torch in that tight spot and I'm pretty damn good with a torch.

 

Right, I was speaking very generally. It would be a little tricky to get heat onto the stock manifold collector bolts without burning other things. The y-pipe would be pretty easy, but if those are that frozen, I just let them break off and replace them with stainless bolts anyways.