Higgite's link is worth a read.
I did buy a gallon can of WD-40 years ago when I was Parkerizing things. It is less expensive than Brownells' water displacing oil, even though it is a brand name item.
I watched a YouTube video about penetrants, applying them to rusted lugs and measuring the torque required to loosen them and that found Kroil not doing as well as any other item tried, though it did cost the most. That annoyed me because I have two cans of it. The top performer, beating both Kroil and PB Blaster and several other items was Liquid Wrench pro series penetrants. The video is here. Skip to 8:25 to see the comparison data. The problem is, you can look at the data and see the highest torque needed to break a lug nut with Liquid Wrench is above the lowest value for other penetrants, so there is enough overlap not to have a great deal of confidence in the relative mean values, especially for the all the rest other than Liquid Wrench. He needs more than four lugs per test. Nonetheless, the whole experiment casts a lot of doubt on conventional wisdom about what to use as a penetrating oil.
I did buy a gallon can of WD-40 years ago when I was Parkerizing things. It is less expensive than Brownells' water displacing oil, even though it is a brand name item.
I watched a YouTube video about penetrants, applying them to rusted lugs and measuring the torque required to loosen them and that found Kroil not doing as well as any other item tried, though it did cost the most. That annoyed me because I have two cans of it. The top performer, beating both Kroil and PB Blaster and several other items was Liquid Wrench pro series penetrants. The video is here. Skip to 8:25 to see the comparison data. The problem is, you can look at the data and see the highest torque needed to break a lug nut with Liquid Wrench is above the lowest value for other penetrants, so there is enough overlap not to have a great deal of confidence in the relative mean values, especially for the all the rest other than Liquid Wrench. He needs more than four lugs per test. Nonetheless, the whole experiment casts a lot of doubt on conventional wisdom about what to use as a penetrating oil.