I've always used high pressure water to wash everything under the hood....every inch of the engine hot or cold and every wire, plug etc attached to it, fenders, firewall and everything attached to them and the IC, AC condenser, radiator, oil cooler and tranny cooler. Never a problem. No dirty engines allowed in my garage.

 

Handled many a $500 plus repair after being pressure washed.Shoves water in places it would NEVER get.I use GUNK Engine Brite and normal hose on a rinse stream once a year or so.Tried Simple Green and prefer the Gunk.If you really want a engine to shine and not collect dust use Engine clear.Its clear spray paint! Lots of used car depts used it for years.Some auto parts stores use to carry it or any stores with spray paint.I used it too years ago.Might go by some again.Shiney,dosen't attract dust etc.Spray hoses,shrouds etc.Use to get a lot of compliments on my under hoods with it.