I recently had a customer give me a call after power washing the engine on a vehicle he had just purchased. The good news was that the engine looked great! The bad news? Moisture had gotten under his ignition coils which caused the check engine light to turn on and his engine to run poorly.
It is our opinion here at Gustafson Brothers that you should not wash your engine if you are not experienced to do so. Unless there has been a major fluid leak it's not necessary to wash your engine compartment. In todays modern engine compartment there are too many electrical components that run the risk of being damaged by washing.
A nice clean engine looks great, but we prefer you have one that runs great. Driveability problems, check engine lights and possible computer damage make engine washing mostly a thing of the past.