I do not know if it is allowed or not, but I clean my FJ (engine too) when it is real dirty at the car wash by the Post Office on Delaware St in San Mateo. It is a coin-op, with high pressure good for getting Hollister mud off.
The address for the post office is, 1630 S Delaware St, San Mateo, CA. The car wash is just North of the post office.
actually, that would be pretty cool. a buddy of mine used to work in a shop and they had one. used it on my old engine to make it all sparkly clean. it even tore off old chipping paint from what i recollect.