For 45 years, I earned the bulk of my living twisting wrenches, and in that time I've come across more frozen fasteners and tried more types of penetrating oil than most of you have had hot meals—and not once through all those busted bolts have I ever seen a penetrating oil that cut through corrosion better than Promech Professional Mechanics Formula Penetrating Oil.
What's in Promech, I couldn't tell you if I wanted to. I can tell you that it uses a wicking action to penetrate corrosion-seized fasteners, and that it works really well at freeing hardware seized by galvanic action, which occurs when dissimilar metals are threaded together and then subjected to moisture. It's a problem common to motorcycles, which tend to have lots of steel screws threaded directly into aluminum. I can also tell you that it seems to work equally well no matter what position the fasteners are in, a huge advantage when you're on your back trying to free that recalcitrant screw directly overhead.
Understand that Promech is not a universal rust buster/cleaner, like your typical moisture-displacing lubricants are. For starters it's far more aggressive at dissolving rust and corrosion than any over-the-counter product, and in fact needs to be used with some caution, as it can damage certain types of paint and plastic. Furthermore, Promech isn't a lubricant, although it does have some lubricating properties. Promech's sole purpose is to migrate into threads and break down corrosion that's locking things up so you can separate parts without damaging them. After using the stuff on everything from old motorcycles to not-so-new tractors for the last few weeks, I can tell you that it does that exceedingly well. — Mark Zimmerman
Professional Mechanics Formula Penetrating Oil
Price: $8.95. (4 stars.)