VARIATIONS
Radiator caps are generally one of two types, solid or pressure relief:Solid caps will have no external pressure relief valve. To remove this type of cap, cover it with a thick towel before turning it to the first stop. Allow pressure, if any, to be released from the radiator. Push down on the cap, again using a protective cloth, and rotate it counterclockwise to remove.
Pressure relief caps permit cooling system pressure to be released without loosening the cap. Valves can either be push-button, lever, or swivel. Push the button, pull the lever, or turn the swivel as appropriate to relieve the pressure. When the air sound is no longer heard, the cap is safe to remove.
Pressure ratings vary generally from 14-16 psi. Any pressure buildup above this point is released.