BMW 440i xDrive Gran Coupe Pressure Test Radiator Cap at your home or office.

What is the radiator cap pressure test all about?

In a pressurized cooling system like those found on all cars, your car’s radiator cap is calibrated to seal in coolant to a particular pressure point, then allow some vapor to escape once that threshold has been reached. The ejected fluid is piped into the overflow bottle you might have seen in the engine bay. Then, as the engine cools, the coolant level may drop inside radiator. When that happens, a reverse-flow valve in the radiator cap opens to allow fluid from the bottle to return to the radiator. A radiator cap that isn’t working properly may cause too much fluid to escape the system.