It has long been said that if something doesn’t move, but should, use WD-40. But what if you’re trying to free a rusted bolt? You can do better than that...

One of the more popular penetrants is PB B’laster. The styrofoam cup test is a favorite method when comparing it to WD-40. But there are also other penetrating oils on the market that claim to be better. So Machinist’s Workshop magazine published an article in their April/May 2007 issue, recounting the writer’s attempt to create a controlled environment in which to test each substance. The method went far beyond melting cups, focusing on resistance.

PENETRATING OIL - AVERAGE LOAD

None - 516 pounds
WD-40 - 238 pounds
PB B’laster - 214 pounds
Liquid Wrench - 127 pounds
Kano Kroil - 106 pounds
ATF / Acetone Mix - 53 pounds

The test showed that anything, even WD-40, was better than dry-wrenching. But the winner, by a considerable margin, was the home-made mix consisting of 50% automatic transmission fluid, and 50% acetone. This 1:1 ratio allows the thin acetone to carry lubricant deep into the threads of your target bolt.

The ingredients are easy to come by. Acetone can be found among paint stripping chemicals at your favorite hardware store, or you can find it in nail polish remover.

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But ATF and acetone don’t like to stay mixed. The home brew will separate overnight, and is therefore a “shake well before use” product. To facilitate mixing, I avoid keeping it in a spray bottle (which would hold the first few squirts of fluid in the straw). Instead, I use two containers:

I start with the 16oz bottle, adding 6oz of acetone & 6oz of ATF. This leaves room for mixing. After a good shake, the mixture gets poured into a little 4oz bottle that previously held friction modifier for my differential. This little bottle has a nozzle on top. I refill the little applicator bottle as necessary, then mix up a new batch once the 16oz bottle is empty.

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This solution works great, but the test featured in Machinist’s Workshop is over 8 years old. Is it time for a new test? Are there better formulas out there?