Stock 216 1/2 ton truck engines came with 0 psi radiator caps and 150-160 degree thermostats.

Full-pressure standard 235 1/2 ton 1954 truck engines came with 4 psi radiator caps and 150-160 thermostats.

Even good engine rebuilders not always carefully cleaned out the rear-most end of the block. This is one significant contribution to a hot engine (that has a good radiator).