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: Checking Radiator Cap
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Apply a pressure of 93-123 kPa (0.95-1.25 kgf/cm² , 13.5-17.8 psi).
Check for a drop in pressure.
If the pressure drops, replace the radiator cap.