I know, we've all heard that one before. But, this one works great! In preparation for pressure washing my '89 YJ tub, I liberally sprayed Castrol Super Clean to the entire underside the night before. This morning, I sprayed it down again. I used a 25º tip, moving slowly and maintaining a distance of no more than 2 inches away. Much to my surprise, the undercoating was disappearing. I mean, completely! I can't say if the Super Clean had anything to do with loosening up the undercoating. It took me about an hour and a half to remove every spec of it.