Is propane good enough for heating stuck bolts?

About to take out the leaf springs on the old XJ and I've spent a couple weeks now heating the bolt heads with propane and soaking in PB before I start in on em. I'll spend like 5 mins or more a bolt just heating right on it but it still doesn't seem like it gets the thing hot all the way through. It never does get close to red hot. Is propane gas hot enough? The MAP/PRO stuff only gets like 150F hotter so it'd hardly be worth it specially since it costs 3x more.

Metal expands when heated. Heating the head of a bolt does nothing but waste time and gas.
Heat the nut and then break loose while hot.

Actually, all you have done is burn off the BP.

It is my opinion that using a plumber's propane torch to heat a rusted/frozen bolt works just fine. I did exactly this when I added quick disconnects to my front end. In my mind, heating the bolt just expands everything and makes it tighter...but in reality, it loosens the bolts. Not sure why. But in my limited experience, a propane torch will help unstick a bolt.
I also used this on the NUT on my emergency brake cables.

Good luck.

Thanks for the advice. Best advice I"ve gotten so far is that rust is broken up better by rapid heating and cooling , expanding and contracting the metal. This requires quenching, and one suggests using PB to do this with as the heat will draw the stuff into the joint.

I'm mostly concerned with my rear upper shock bolts, only the heads of which are exposed. And the bar pins make getting any PB in there difficult. We'll see.

Yep, propane works fine. Worked at one shop where we had a small propane torch for heating tie rod end nuts and stuff. In my experience, the biggest problem with XJ leaf spring bolts is them getting seized in the bushing liner. Applying some pressure to the leaf spring with a jack seems to help with this.

BTW: You are almost certainly going to spin off the heads of the bolts for your upper, rear shocks. At least one of them (there are two on each side). Spray them with PB B. from the bottom every night for a week (don't spay PB inside the cab. You will never get the smell out). Then hope for the best. Have carbide bits on hand to drill out the bolts and a tap set to re-work the threads. And cutting oil. Despite what people say, you shouldn't have to drill out the threads and use a larger tap. If you drill center and true, you should be able to re-tap the same holes with the same size tap and run new bolts in. Or you can cut off the welded nuts from the top side. If you have one broken bolt, drill it out. If all four break, you may want to to cut off the nuts...but fishing bolts through the holes is a PITA. I would drill em and tap em. This is a matter of personal preference.

I think you meant cobalt instead of carbide. Good HSS bits work just fine. While its certainly possible to drill the bolt out so you don't need to go up a size, it can be difficult to do without a lot of experience. If you're off center much at all you will be upsizing. In my experience an impact wrench is far less likely to break certain bolts. If there's any doubt go forwards then backwards until they start moving. MAPP does work better than propane. You need a real oxy/acetylene torch to get things real hot. Without the use of an impact wrench you probably need at least a 3 foot breaker bar to get the leaf spring bolts moving.

Cobalt: Yeah. I did. Thanks!

I've experienced the rusted leaf eye bolt to the sleeve. The welded nut may break loose. Had to cut a hole in the frame for a replacement nut. I didn't have a welder at the time so the hole had to large enough for a wrench to hold the nut.

When I pulled my leafs I cut the bolts after breaking them loose. They were rusted to the bushing sleeves. An angle grinder and 5 minutes is all I needed. You have to break them loose first otherwise you'll never get the threads out. New bolts and anti seize will help.