The max pressure on the washer I used was set at 1500psi. Other than knocking loose the wire to the pressure switch on the a/c receiver/dryer, all seems to be okay.

I went through the Detroit Diesel apprentice program in '81 and '82 with a GM Diesel outfit in Seattle; a two year deal. Whenever over the road trucks came to the shop for ANY sort of service; from mild to major overhaul, the engine and drivetrain components always received a MAJOR cleaning before and after the work was performed. Now, in that shop that routinely had anywhere from thirty trucks in the shop on a given day, the pressure washer system was plumbed-in from the shop's live steam heat system - true steam cleaning at around 2800psi. No question about it, it was a matter of course that every engine was douched that way. The pressure wand was simply stuck down into a 55 gallon drum and ran ALL day long and into the night (a 24 hour shop). The 55 gallon drum would just stay full of scalding hot water and run over onto the pavement outside the shop. That is, until one day, the guy who ran the dyno shed somehow knocked the drum over with a forklift and sent another tech to the hospital with third degree burns on his feet and lower legs. OSHA stepped-in at that point and the pressure wand had to have a 'dead-man' trigger on it after that. It's pretty common sense not to hit carburetors, distributrors, the alternator and so on. My original question really had more to do with the danger of cracking an aluminum head. What prompted that was a memory of a neighbor who owned an Alfa Romeo GTV-6. He thought you were supposed to pressure wash the engine with it still running and so, cracked a head right where a spark plug boss happened to be. Even a Heli-coil wouldn't save it.

I don't know if there's any truth to the adage I once heard; that a clean engine runs clean?