Stuck fill plug, how to attack?

My wife requested full fluid changes on her 2007 FJ Cruiser before summer. The fill plug on the rear differetial is stuck. It was half stripped before I touched it, but now it's all the way stripped. Luckily I was smart enough to not drain the fluid first, but I still have a problem here. I'd rather not have to pull the rear end and have the plug drilled and tapped, but I'm running out of ideas. It's currently soaking with PB Blaster and horrifyingly, the tool that best grabs it is a pipe wrench. It's not moving.
So where do I go from here?

Heat it a bit (not a lot) and then re-soak it in PB blaster a few times as it cools. If that doesn't do the trick, try tapping on it with a hammer a few times and/or hitting it with a can of freeze spray.

yeah, heat the area around it, not the plug itself. Whack the plug with a hammer.

Sometimes a bolt can be 'one way' stripped. if that is the case, you can try tightening it just a tad to break the threads loose and then it backs out much easier.

Don't forget to buy a new plug before destroying the old one trying to get it out.

EDIT: I doubt heat/oil will help what with it already being coated in gear lube, I'd guess it was over tightened with the wrong socket.

Headed to get a torch after I pick up the kids from school. I'll try the heat/quench thing a few time. I have an old 'hit it with a hammer' impact driver that failed to do anything while there were still flat edges on the plug.

Heat, and a air chisel on the edge to force it loose should work, if not and you've exhausted other ideas, you could use a cut off wheel and make new, larger flat spots to grab more securely with a pipe wrench.

I once replaced a transmission and only discovered after it was in that the fill plug was completely boogered up and would not accept the proper sized allen key. I ran a small diameter hose down to the vent and did an "IV drip" overnight to fill it with fluid

I've used a grinder/dremel to shape a rounded plug/nut into a smaller hex. Keep testing until an impact socket is tight then hammer it on.

When you can get a good bite on it try hitting the handle of the breaker bar to jar it loose instead of pushing gradually. The shock can break the threads free.

Good luck!

mostly whats covered, not sure on a landcruiser but most diff plugs are taper fit and a giant pain to get out if someone over cranks them. Ive had the best luck using the torch method or drilling a hole dead center. An old guy i used to work with swears buy heating and melting candle wax into the threads, never tryed it but might be worth a shot.

In reply to KyAllroad:

Straight up hammering on a stupid 12 pt socket can work too.

Weld a nut on it?

I would try heat.

Realistically, if Toyota only wants you to torque the damn thing to 36lbft, they really shouldn't put such a big bolt on it that it looks like it needs to be torqued to 100+.

So if a pipe wrench grips it, what is the problem? Just scared to lean on it and possibly strip it worse?

If you still have this problem on Saturday i can try to bring a couple things with me and give it a shot.

A pipe wrench is the proper tool for this job. It has the advantage of getting tighter as you put pressure to it. That and heat. I usually put a decent amount of pressure to it and add heat until something gives. The wrench has the added benefit of being a heat-sink on the plug and keeping it cooler than the surrounding metal.

I assure you I put a LOT of torque into it in increasing amounts through the afternoon. It's now been heated three times and is sitting with PB Blaster on it for the night. It did not budge after the hearing/cooling. At this point I'm getting concerned that too much more destructive effort could damage the housing. This was supposed to be preventative maintenance after all.

do you have a four foot pipe you can slide over the end of the pipe wrench? Even if you can only get a couple inches of travel you can reset it and go at it again till it gets loose.

I have put enough force into it through a pipe and a floor jack to tear the metal with the pipe wrench. I haven't broken the pipe wrench yet, so I can still go farther. Tomorrow.

You were heating not the plug but the surrounding metal right? And trying to loosen right away while the metal is hot?

Did anybody say shotgun yet?

No? Ok. Shotgun.

It might be worth trying a can of CRC Freeze Spray or similar to contract the plug itself. Also, is there any chance someone staked the threads so that it couldn't come loose accidently?

When you heat something, it expands. If you're heating the plug, you're making it tighter in the hole by that expansion.

The only times I've seen this work is when you heat the plug to red hot. Then, in the right hands, it can magically start coming out. I say in the right hands because those hands are not mine. I've never mastered this technique, even when working beside one who has mastered it.

Since you mentioned it being half stripped in the initial post, I suspect the threads are solidly boogered now, and you are dealing with mechanical damage, not mere rust binding or simple over torquing. So this plug isn't going to simply break free and unthread, it's going to take force all the way out.

Next time, fix the threads before you run the plug or bolt back in.

You may well end up wringing the end off this plug. At which point you're going to be drilling the plug out. Grease up the drill bit and you can catch most of the metal, but not all of it.

You can also simply give up on this and refill by measured quantity through the vent as described above, or through the bottom drain plug.

When you heat it (not just red, orange/yellow!) the metal gets softer and when it tries to expand it crushes itself. And, being softer, it deforms more easily.

This is why heating a stud yellow will allow you to get a nut off over it, even though technically it is expanding.

Despite what the Intenet would tell you, steel softens immensely when subjected to intense direct heat

Heat the plug, and heres why. You heat it, it expands..you wait a few min and it cools, metal shrinks .001 ever 100f per inch of metal. Heat it 400 let it cool to 100*? Bingo you just shrunk it .003 if its as big a bolt as you say it is. Also try one of the iriwin brand bolt extractor sets from home depot or whaterever they have done me right before

Grab a 3 inch long section of 1x1 angle iron. Weld it to the plug. the welding will heat the plug and you now have a hammer surface with leverage. note you may have to cut the angle to spin the plug all the way out but once its moved a 1/4 turn your almost done. You could weld a nut to it as was suggested above but that may not give you enough torqueing surface.