Coolant Reservoir Cap Pressure

Caps are designed to ensure that the prescribed pressure on the cooling system is maintained at all times during operation by allowing air to escape in case of overpressure.

Coolant reservoir cap pressure.

Cutaway of radiator cap and reservoir. If your cap isn t venting this causes excess pressure in the cooling system and can cause leaks or a collapsed radiator hose. The constant need to add coolant can also be caused by a leak somewhere else on the engine so a proper diagnosis is recommended. A reservoir is under pressure in normal circumstances in order to increase the coolant s boiling point.

At operating temperature coolant can evaporate from the open system. How does this simple cap do this. The radiator cap and expansion tank cap make sure the filling hole of the radiator and expansion tank are sealed off gastight. The radiator cap releases the extra pressure by sending some coolant into the overflow tank.

But they do a lot more than just that. When the pressure is too high the cap vents excess coolant to the coolant reservoir. A cap that is no longer sealing could also cause a leak. Coolant goes into the reservoir tank as it expands.

While you re in there check to make sure your coolant overflow tank is working properly. Another symptom of a potential problem with the coolant reservoir is coolant leaks. The cap is actually a pressure release valve and on cars it is usually set to 15 psi. The radiator cap actually increases the boiling point of your coolant by about 45 f 25 c.

In case of a faulty radiator cap the required pressure fails to build up inside the system leading to overheating.