Any history on this truck? Been driven at all? Did this start following any work, or gradually, or out of the blue, or . . .
Belt tension tight?
Running with the thermostat out DOESN'T change anything?! I guess that rules out vapor lock at the 'stat. General wisdom is to drill one or two small holes in the flange of the 'stat to allow air to escape on first start-up. But don't, as a rule, run without the 'stat in.
Seems like that would say that either the water isn't circulating properly, or that even if it is, it isn't up to the task.
Blockage in the block?
Mine ran lean for a while, overheated, even with a properly functioning cooling system. Pulling the choke out a little made it cool off immediately, but it had to be just the right amount.
-Michael
