I've always gone to the car wash to spray their "engine cleaner" on & rinse off. I try not to drown the engine when rinsing off, but you're safe as long as it's running and the alt stays clear of direct spray. Nowadays, I do this in my driveway (since I just bought a house... woohoo&#33 with zip wax & water, and it's just as good. I took my Yukon ('02) to the dealer for an alt swap, and the tech in back said that's got to be the cleanest engine bay he's worked on.