I wash my engine compartment everytime I wash my SVT. I use good old ZipWax car wash. I hose everything under the hood and never have any problems. Same goes for my 99 Powerstroke, my 99 Lincoln TownCar and my Supercharged 85 Mustang 5.0L. Been doing it to my cars for over 30 years and have never had any problems; but, I do always have clean engines! Just don't do it hot!