Radiator Cap

The Radiator Cap is a small but vital component to the Z32's cooling system. It is inexpensive and easy to replace, making it good "infrequent maintenance" part.

Operation

The Z32's cooling system is under pressure when it's hot. This is intentional, as the pressure raises the boiling point of the coolant, as the boil would otherwise have to overcome the pressure.
However, too much pressure is a bad thing, and can cause leaks, which would lead to no pressure. The radiator cap regulates the pressure in the cooling system to maintain it at approximately 1.2 bar (17 PSI). Under extreme conditions, the cooling system's pressure will exceed this threshold. At this point, the spring-diaphragm in the radiator cap backs off slightly to allow excess coolant to bleed into the overflow tank. Once the cooling system has had a chance to cool down, the coolant contracts as its temperature drops, and eventually draws the excess coolant back from the overflow tank and back into the radiator.

Aftermarket Radiator Caps

There are various aftermarket radiator caps available, such as those included with Mishimoto Radiators. It is highly recommended to stick to a stock radiator cap, as aftermarket versions tend to be inconsistent and unreliable. Those rated for higher pressures may also put additional stress on the cooling system, creating leaks and causing hoses to burst.