If any one of them shows visible damage, replace the cap with a new one.
Install the cap [A] on a cooling system pressure tester [B].
Note. Wet the cap sealing surfaces with water or coolant to prevent pressure teaks.
Watching the pressure gauge, pump the pressure tester to build up the pressure until the relief valve opens: the gauge hand flicks downward. Stop pumping and measure leak time at once. The relief valve must open within the specified range in the table below and the gauge hand must remain within the same range at least 6 seconds.
Radiator cap relief pressure
Standard: 93-123 kPa (0.95-1.25 kg/cm2, 14-18 psi)
If the cap cannot hold the specified pressure, or if it holds too much pressure, replace it with a new one.