Radiator Cap Test

Wait until the engine is cool, then carefully remove the radiator cap (A), Wet the radiator cap seal with engine coolant, then install it on a commercially available pressure tester (B).

Fig 1: Applying Pressure On Pressure Tester Attached To Radiator Cap Seal
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Apply a pressure of 93.3-122.7 kPa (0.951-1.251 kgf/cm² , 13.53-17, 80 psi).
Check for a drop in pressure.
If the pressure drops, replace the radiator cap.