Original equipment on AD trucks were not high pressure radiator caps and did
not operate at todays boiling temperatures. I think that up to a point they
were non pressure caps and ran at 180 degrees or less as the norm. I'm not
sure when the pressure thing started but something tells me that the first
ones were around 2.5 to 3 psi. The old ones ran a lot farther from the edge of
boiling when everything was right. If one of the oldies boils in just a short
time of running at any speed I would be flushing engine, radiator and checking
thermostat in a pan of water with an accurate thermometer. The cooling system
in my 51 is certainly not as marginal as the one in my 1997 model. I don't
think the water pumps were built to handle pressures like we see today either.
Dave Handley
51 GMC 5 window
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