What I used to do when I detailed cars was to first spray the engine down with a degreaser, something like Simple Green, and flush it off with a pressure washer. Make sure you keep the engine RUNNING, keep water away from electronics. After it has air dryed, spray the entire engine down with Armor All. It is important to wash the engine before buffing and waxing, because the degreaser will leave streaks in the paint, and these will come right out with the buffing.
