You can test the thermostat in a pot of water above the rated temperature of the thermostat. Put it in and see if it opens. You can run the truck without it to see what happens. It is designed to stay closed until the rated temperature is reached and then open. This gets your engine up to temperature as fast as it can. There is a wax filled capsule that melts at temp and expands to open the valve. It wouldn't hurt to try it without it to see what happens. You could have a hose collapsing on the suction side of the water pump. A fuel mixture that is way to lean will burn to hot. You can bypass the heater with a hose for the time being. Could be a stopped up radiator. I have seen the fan on backwards but that would show up when you were driving at the speed to cancel the air blowing through the radiator with the fan blowing through. Test the thermostat and go from there.
EDIT: Boy you guys are fast by the time I finished typing you had already said it all.
Last edited by neilroy; 04/01/2009 2:19 AM.
