Looking at specs in the 1950s and 1960s there is of course a steady rise in cooling system pressure from around 4 pounds to 16 pounds. It is often said that even if a newer radiator is used a vintage system may not hold up - heater core for example.

In '64 the trucks used a 7 pound cap, but earlier identically engined cars (sometimes) used a 13 pound cap. What was the determining factor at that time whether a vehicle used different pressure radiator caps? Could it be the coolant - "Permanent" type glycol was a relatively new product, and this choice affected the thermostat selection?

Fast forward today, assuming we could run a higher pressure cap than was used for a given model at the time - do we want to? Is there an advantage to running a higher pressure radiator cap provided it is still within the specs of the radiator or heater core? I ran a 16 pound cap for quite a while until I was advised not to do so, it certainly led to very rigid upper radiator hose as I recall.