A leaking head gasket on a truck engine is possible but very uncommon. That wouldn't be by first suspicion without doing at least a pressure test. If the leak is so slow that the coolant evaporates before hitting the ground, adding a small bottle of dye can be a useful aid in finding the source of the leak.
Speaking of a leak, what is the symptom indicating the coolant is leaking? Do you see it coming out someplace or is the level just going down in the reservoir?
To check the water pump, grab the fan blade and wiggle it back and forth. If the pulley moves too, the bearings in the pump are worn. That will allow the shaft to move away from the rubber lip seal and coolant will leak out from behind that pulley. That will only get worse. When that pulley tips even a little, the belt actually slides sideways across it as it goes around it. That's what sets up the squeal.
If the fan blade has looseness but the pulley doesn't move at all, that's a sign of a worn bearing in the fan clutch, and it won't cause a belt squeal. You should also be able to turn the fan by hand, (engine not running, of course), but there should be some resistance. It will spin easier when the engine is cold.
Tuesday, October 9th, 2012 AT 8:10 PM