Originally Posted By: MetalSlug
Originally Posted By: AVB
Is that picture of your truck?
Yes, I know it dirty, im scare to hose it down, since the knock sensor it under the intake, water get in and have to remove the intake.
When I worked at an auto auction we pressure washed the engine bays of GMT800 trucks all the time...none of them ever died or had problems from it while we had them. I think you would be safe hosing it down with the engine either cool or running, just take it for a drive afterwards to dry everything out.
Coolant leaks can be very intermittent and show up when they want to. My Explorer would spray coolant all over the engine from what I and a couple shops guessed was the intake manifold, but nobody could ever track it down for sure, so I left it alone. I never topped it off because the level never got low in the reservoir, but every couple weeks the telltale white coolant spray would show up. Just keep an eye on it and try to catch it when it's wet. Top off the reservoir as needed and track how much it's using.
FWIW, head gasket leaks can be internal, external, or both. So you may have a leaking head gasket, but if it's external only, you won't get any coolant in the oil. Likewise, a head gasket can leak internally, mixing oil and coolant, but show no leaks on the outside.
Your mechanic has actually seen the engine up close, and we have not, so for now I'd go with his diagnosis.