I use Purple Power mixed with 2-3 parts water in one of those pump-up sprayers. It's terrific for degreasing engines and scrubbing dirty wheels and tires, and it's very cheap if you buy the 2.5-gal size. It's gentle enough to use on automotive paint for removing tar and stubborn stuff from lower body panels, although it will strip the wax too. I use it for other stuff around the house too, like the garage floor and garbage cans.