The original 1953 thermostat would have been rated around 160 degrees: starting to open at around 150 degrees and fully open around 180 degrees.
4 psi radiator cap
The 1954 high-pressure 235 in my Suburban would not reach operating temperature (160 degrees) when running and sitting still and with no thermostat. This was with a cleaned block-interior and new-core original radiator.
