Why are radiator caps pressurized?

Radiator caps are pressurized to raise the boiling point of the coolant in the vehicle's cooling system. When the cooling system is pressurized, it prevents the coolant from boiling at its normal boiling point, which is typically around 212°F (100°C) at atmospheric pressure.

By pressurizing the system, the boiling point increases; for instance, a pressure increase to 15 psi can raise the boiling point to about 245°F (118°C). This is crucial because it allows the engine to operate at higher temperatures without the coolant turning into steam, which could lead to overheating and engine damage.

Additionally, the pressurized environment ensures that coolant remains in a liquid state under operational conditions, which is vital for effective heat transfer from the engine. This also supports the overall efficiency of the cooling system, helping maintain optimal engine temperatures.