Originally Posted by Exit1965
It's a direct drive fan. I didn't try a wobble check but will try that. There is some kinda rotational noise now that you mention it, though it's subtle and I haven't tried to pinpoint it. There is no heater on the truck anymore, so that outlet on the water pump is capped.

Thanks for the ideas. I'll see what it does without the thermostat in it tomorrow. Would I expect to see lots of activity in there if the pump was working OK?

You should see the same activity with the stat open and the engine at 2K or more RPM. If not I would suspect a slipping belt, Impeller not turning, (off the shaft, loose on the shaft or broken shaft) or a blockage. keep in mind the blockage can be a plugged radiator, collapsing lower hose, T'stat not opening or installed upside down. Something is keeping the water from flowing, the question is WHAT ? Keep us posted twocents beer

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