What is Penetrating Oil?

If you are an auto hobbyist, young machinist, do-it-yourselfer or avid tinkerer, you might have heard the time period "penetrating oil." Penetrating oil is an umbrella term that refers to a class of lubricants with a skinny, water-like consistency, similar to WD-forty, Kroil, PB Blaster and Zep. These low-viscosity lubricants are completely different than thick-film or [...]