“Know thy engine bay!”
As you already know, pressure washing an engine can be done, but there are potential problems.
BEFORE firing up the Pwasher, identify possible problem areas to avoid. If necessary cover them with heavy plastic and duct tape; this will only protect from overspray as the Pwasher can turn plastic to spaghetti. The plastic also serves as a visual reminder “don’t spray here”.
Electrical connectors- already mentioned.
Water in the intake- not likely unless parts are removed; but how many Trucks have you seen with the Cold air snorkel removed?
Heat exchanger fins- a pressure washer will fold a LOT of these over in a fraction of a second, blocking air flow/killing the effectiveness of the radiator, CAC, tranny cooler, etc. Granted, this is more of a front end/ grill cleaning issue; but after blowing greasy crap all over with a pressure washer, what will we use to rinse off the outside of our vehicle??
And I definitely agree with the warm (not hot) engine (if oiliness is the problem). Take a trip, let it sit 15-30 minutes with the hood closed. Spray away. The heat really softens the thick junk.