The higher the pressure, the higher the boiling point of the coolant....higher is usually better. However, sometimes a high pressure coolant system can reveal/cause other problems.....like weak spots in the system.....bad hose, thin spot in radiator/heater core, etc...
Radiator Cap Get a 15 pound rated cap. 68's came with no overflow tank. The cap should not relieve until it needs to as a safety release measure. Some radiator shop put a 7 pound one on my car and it took me most of a year to figure out why it wanted to boil over whenever I shut it down. 15 pound cap, problem solved.
I agree with John. My '69 GS California has a 15 lb on it and no overflow tank. Only spits a little coolant on very hot days after shutdown. Talking just a wet mark on the pavement, not green pi_ s everywhere. Overflow tank from a Vega/Monza or Nova bolts on and looks factory. Easy to find as well. Jim '69 CS California 455 Stage 1 Muncie M20 4-spd 3.31 Posi
