Remove transmission fill plug, hot or cold trans?

Just thinking, that transmission case is aluminum and the plug is steel, would it be safest for the threads to remove it cold?
Just curious if people usually remove the plug (break it free after a year or more) warm or cold.
I know spark plugs in aluminum heads should be removed and installed in a cold engine.
Thanks.

 

Manual transmission, I assume? I don't think it matters, I've done it both hot and cold. Just don't over torque it when reinstalling.

 

No, automatic.
Thanks.

 

I always do it cold as the area around the plugs get real hot after driving. Save myself from a burn.

 

The transmission doesn't care. However, access to the fill plug is right by the exhaust pipe and catalytic converter, so it's best to wait until it's cooled down.

 

You've got a better chance burning your hand from the hot exhaust pipe than damaging threads in the transmission case.

 

^^^^This^^^^
I'll go further: "Over-Night cold". Aluminum cools faster than the iron/steel the plug is made of and will shrink around the plug and effectively lock it in place until the temperatures equalize.

I stripped the threads in a Volvo head one time removing a spark plug on a warm engine. It felt no different removing it than all the other times I changed the plug on that engine over it's 300,000+ mile life. As soon as I tried installing the new plug and it wouldn't go, I knew something was wrong.

Helicoil fixed it, and I never did the plugs on anything again unless the engine was fully cold even if it had cast-iron head. I had the plugs done on my Tacoma by a local shop that agreed to drive it into the bay the night before and do the work on a fully cold engine first thing in the morning. I explained why and he immediately agreed. I dropped it off the night before.)

 

The automatic transmission pan is iron. Easily checked with a magnet.

 

It doesn’t matter.
I prefer cool, because who likes hot fluid running down their arm?

The important part is is getting the fluid level correct.

 

It was the fill plug I was concerned with, not the pan. But I removed it just fine after it was cool.
Thanks to all for the replies, got the fluid refreshed, and the old stuff didn't look too bad. I did one drain and fill two years ago. I believe this truck had regular fluid changes before I got it. 325k miles and it shifts well, only a very infrequent shudder but only in overdrive.