In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.
The coolant will typically only build to 16-18 PSI, due to expansion up to 200°F. However, if the engine does overheat due to external factors, the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off. The radiator cap is basically a "safety valve", so always use the highest pressure radiator cap that the radiator will tolerate. If you are unsure of the pressure rating for your radiator, check with the manufacturer for the maximum recommended operating pressure.
performance radiators will accept 22-24 PSI