How do I loosen a very, very rusted nut off a bolt from under my sink?

try using wd 40

Spray it with WD40 that should help loosen it up

Hello Barry; As the other ladies stated, WD40 is the best for that. I would also add a damp cloth after spraying the heck out of it and let it sit for several hours! This should help it loosen, ever more! I hope that this helps. Take Care.

hardware stores and car care centers usually carry something for that, but I can't think of the name..you could also try pressing some "white grease" (not an animal product0 into the contact points, wait awile for it to be absorbed a bit, then wrench it baby!!Or hold a hairdryer on the high heat settin on the bolt only, then when it is heated, torque it with the wrench ..Don't bang it first or you'll just jet rust tust tighter around the bolt threads

Have you tried spraying with WD 40 or some type of lubricant.

There is a product called Kano Labs Aero Kroil that works wonders. It seem to penetrate like nothing else I have used. Spray it all around the joint and let it soak for few minutes . Saturate the area again and let it soak for a few hours. If it still doesn't come loose, don't despair. Try one more time and let it soak overnight. If this doesn't work I don't know what will. I take a lot of junk apart and has been the best. It is not cheap, but it lasts a long time and goes a long way. I have no affiliation with the makers of this product and I don't sell it either (even though I may sound like a salesperson) Just a big fan.

You are dealing with a potential water problem if this is done incorrectly...I would definitely get the advice of a plumber before you attempt it yourself

I have used PB Blaster on rusted nuts and bolts. Better than WD40. All else fails you'll have to cut it off. A Dremel will work.