Remove the radiator cap, wet its seal with engine coolant, then install it on a pressure tester.
Apply a pressure of 93.16 ~ 122.58 kpa (0.95 ~ 1.25 kg/cm², 13.51 ~ 17.78 psi).
Check for a drop in pressure.
If the pressure drops, replace the cap.
Wait until engine is cool, then carefully remove the radiator cap and fill the radiator with engine coolant, then install it on the pressure tester.
Apply a pressure tester to the radiator and apply a pressure of 93.16 ~ 122.58 kpa (0.95 ~ 1.25 kg/cm², 13.51 ~ 17.78 psi).
Inspect for engine coolant leaks and a drop in pressure.
Remove the tester and reinstall the radiator cap.
Check for engine oil in coolant and/or coolant in engine oil.