Can a radiator cap test good and still cause problems?
The most common test of a radiator cap is the pressure test. The cap is attached to a fixture, pressure applied and expected to hold the stated amount of pressure. This is ONE test of a radiator cap and test the lower seal and spring only. It is quite common for a cap to pass this test and still cause problems. There is also a top seal that seals the cap to the system and a vacuum valve that allows the cap to vent and still seal. These must be tested separately and many times are not tested or properly inspected. A leaking top seal will allow coolant to leak and can break the syphon effect that allows the coolant reservoir to work.
