Radiator Cap: Inspection

WARNING: This page is about a different car, the 2013 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.

Check that the radiator cap does not have deformation, cracks or damage.
Attach the radiator cap tester to radiator cap.

Fig 1: Inspecting Radiator Cap Using Radiator Cap Tester
Courtesy of SUBARU OF AMERICA, INC.
Increase pressure until the radiator cap tester gauge needle stops. Radiator cap is functioning properly if it holds the service limit pressure for 5 - 6 seconds. Replace the radiator cap if its valve opens at less than the service limit.
Coolant filler tank side:

Standard 93 - 123 kPa (0.95 - 1.25 kg/cm ² , 14 - 18 psi)

Limit 83 kPa (0.85 kg/cm ² , 12 psi)

Radiator side:

Standard 122 - 152 kPa (1.24 - 1.55 kg/cm ² , 18 - 22 psi)

Limit 112 kPa (1.14 kg/cm ² , 16 psi)
CAUTION:
- Be sure to remove foreign matter and rust from the cap in advance. Otherwise, results of pressure test will be incorrect.
- Do not confuse the cap of coolant filler tank and cap of radiator.