(This post comes from Matthew Wright, Auto Repair Guide at About.com.)

I've known far too many car owners who have popped their hoods at the local spray booth car wash, turned the dial selector to "Engine Bright" or something similar, and blasted away at their engine bay. Sometimes they get away with this and drive away with a shiny engine. Of course, these are the times I don't hear about. When things go bad, that's when I get the phone calls. It's never been a good idea to blast your engine with a high-powered stream of water. Even in the old days, a tiny amount of water under the distributor cap could strand you at the car wash. Now more than ever, there are delicate components in there that can really be damaged by all that water. If you must clean your engine bay, please do so with care.