MP is great at doing what WD-40 does, only better. However, it will not remove rust. It does an outstanding job of preventing it. Many years ago I found a fully rusted wrench somewhere. It was in my very early days after being introduced to Amsoil, so I was still experimenting with it (like putting a quart of 80W-90 gear lube in the freezer at 0°F to see what happened in spite of the claims – it did what it said – I could rock the bottle back and forth and the air bubble would slowly but easily move from one end to the other). So, I brought the wrench home, took some steel wool to it, and shined it up as best I could. I then got a tall jar and made as concentrated a salt water solution as I could, sprayed WD-40 on one half of the wrench, and MP on the other half. I left it out in the garage and forgot about it for a few weeks. When I found it again, I was amazed. The WD-40 end had some rusty spots forming, though it was not entirely rusted either. However, the MP end was entirely rust free. I was truly impressed. Still, over the years, I have no information (or experience) that tells me it will remove rust. It’s “merely” an outstanding synthetic spray lube, with even better protective properties.
And it penetrates its way through heavy rust to allow removal of nuts and bolts better than anything I’ve used. The blade of our lawnmower needed sharpening before use this season, but I simply could not break the bolt loose about a week ago, even after using MP on it for several minutes. I sprayed a little more, and just left it for 24 hours. The next day the first few taps with the wrench produced movement, and after 3 turns or so, I was able to finish getting it out with just my fingers. Upon removal, there had clearly been rust all the way up the threads to the end of the bolt, but it was also clearly lubricated all the way up as well, despite having only been able to apply the lube from the outside of a “frozen” bolt. After decades of use of MP, I was not really surprised, but still very thankful.