Coolant Reservoir Cap Pressure

Another symptom of a potential problem with the coolant reservoir is coolant leaks.

Coolant reservoir cap pressure.

At operating temperature coolant can evaporate from the open system. But they do a lot more than just that. The same way a pressure cooker increases the boiling temperature of water. The cap is actually a pressure release valve and on cars it is usually set to 15 psi.

If your cap isn t venting this causes excess pressure in the cooling system and can cause leaks or a collapsed radiator hose. Cutaway of radiator cap and reservoir. 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.

The radiator cap and expansion tank cap make sure the filling hole of the radiator and expansion tank are sealed off gastight. How does this simple cap do this. In case of a faulty radiator cap the required pressure fails to build up inside the system leading to overheating. While you re in there check to make sure your coolant overflow tank is working properly.

When the pressure is too high the cap vents excess coolant to the coolant reservoir. Coolant goes into the reservoir tank as it expands. The radiator cap actually increases the boiling point of your coolant by about 45 f 25 c. The radiator cap releases the extra pressure by sending some coolant into the overflow tank.

If you have a bad radiator cap the coolant could get released too quickly and cause the reservoir to overflow.