Tried to change my fluid tonight and couldn't get the fill plug out. Not rounded, just won't budge. Is penetrating oil best or heat?

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Hopefully the drain plug is still in!

I would go with penetrating oil first, give it a chance to work and then move to heat later if needed.

If you can't get an impact on it, grind the face of the 24mm socket so it gets a better purchase on the short plug head, and try a breaker bar making sure you don't slip off, or get a mini sledge and give a shorter 1/2" ratchet a good wack while holding the socket firmly on the plug. You can try penetrating fluid but I don't think it will help much, heat always works just not sure I'd want to apply that much heat to the case. You'll be happy you shaved that 24mm down later when you do other drain fill jobs. Make sure it's a 6 point socket and impact sockets are always stronger.

Heat up around the plug (not on the plug but around it), use some penetrant and get onto it with a breaker bar. If you apply a decent amount of force and it doesn't budge, use more heat and more penetrant and try again. You'll get it.

Not sure if you drained it already but you ALWAYS break loose the fill plug first then the drain plug after. People who drain the fluid first and then later find out they stripped the fill plug will have a really good day dealing with that mess.

I would definitely heat it up with a torch (not too much, you don't wan to damage it) and carefully crank on it when it's hot. If you feel like it's going to strip, you stop immediately. As said, penetrating fluid might work as well.

Good suggestion. I had a problem like this with a differential fill plug, many years ago. It was likely my T4R, but I'm not certain.

For jobs like this, I have found that a small butane torch is handy. Very hot, very small flame that you can put the heat precisely where you want it to go. That did the trick on my fill plug.

I had a manual transmission fill plug on an old Nissan that had been rounded over by a previous owner. It was a hard lesson to learn at the time, but I foolishly drained the fluid before trying the fill plug. I tried all kinds of tools, up to a pipe wrench, which I was able to get a solid grip on the plug, however I was unable to turn the wrench enough to do anything. I ended up dropping the transmission, but was still unable break the plug loose. I ended up driving a socket onto the plug as far as I could, then welded it to the plug. This was before online stores existed, so I just left the welded contraption on there after re-installing the transmission.

Thanks for the tips guys. I'm going to buy a 6-point socket, hit it with penetrant and see how it goes. I don't have a grinder to knock it down flat so hopefully it will be ok as is. If that doesn't work I'll try some heat but if rather avoid that if possible.

Oh and I went for the fill plug first for just this reason.

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Does hitting the plug directly with a hammer help to kind of free up the threads?

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I was just about to post that suggestion.

@texadelphia and @TheDurk , good call, first thing I'd do.

My experience with stuck (mainly from rust) bolts is to actually try and tighten it first, just enough to get it to break free. I don't know why, but this almost always seems to work. And when dealing with rusty bolts usually prevents a bolt from breaking or rounding.

But the transmission case is aluminum and if the plug has been over tightened there is potential for thread stripping or even to crack the case itself as Ive seen someone do when forgetting righty tight lefty loosey.

If you can't get it out you can fill it through the shifter.

Bought a cheap impact socket at Lowe's and ground it down past the inner bevel. Tried hitting it with a hammer, and then the breaker bar. Eventually put the propane torch to it which did the trick. The drain plug was equally stubborn. The transfer case plugs came off without heat or anything.

Ran out of daylight before I could get to the front diff. That one has me a little scared.

Applying heat for the win. Heat is your friend for that front diff drain plug as well. I've used it on a guy's rig and it works well. Without the application of heat, you will strip that allen head plug.

Might not be getting to that until spring. Winter seems to have started in earnest here in the PNW.

Is that plug a 10mm allen across the board? I couldn't get a 10mm to go in and the 8mm was too small (don't have a 9) The plug is pretty dirty so it could just have grime build up but I still thought the 10 would still fit.

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