I steamed my old one twice (when I left the oil cap off it )

piece of piss and never missed a beat either time! I even did the top end around the inlet manifold etc.

you're better off using a steam cleaner than a hose pipe as a steamer is just that - more steam than water (if its hot enough).

however I know of a few that have had big probs after doing this so who knows?

take it to a valeter, they're a bit more used to it! (but dont expect them to accept responsibility if it goes tits up!)