I use air, a blowgun with long wand and rubber tip. This is especially good for radiators. Of course, this will not do much for the grease and mud on the underside, where a pressure washer is best. Gunk will help to soften the caked on stuff.
RoosaMaster, for one, warns against getting cold water on a hot injector pump, and you can crack a hot exhaust manifold or turbo housing (if so equipped). Also, I always grease after pressure washing, as a pressure washer can force grease out and water in where grease belongs.