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.

Keep in mind:

• A radiator cap pressure test is quick and simple, and replacement radiator caps are inexpensive.
• Leaving a defective radiator cap in place can cause damage to the engine.

How it's done:

• The vehicle engine is cooled before the radiator cap can be removed
• The radiator pressure is relieved and the cap is removed
• The radiator cap is pressure tested to specifications
• The radiator cap is replaced and/or reinstalled to the radiator
• The vehicle is verified to confirm problem is fixed

Our recommendation:

If your car’s engine overheats, or the overflow bottle seems overly full, have the radiator (and radiator cap) pressure tested.

What are the common symptoms indicating you need to pressure test the radiator cap?

• Car overheats
• Car’s overflow bottle fills up

How important is this service?

Not having this safety valve on the car’s cooling system operate properly can over- or under-pressurize the system, leading to damage to hoses, the radiator, and even the car’s cylinder head.