The material covered by this specification comes in a kit consisting of a cleaning compound, a conditioner and an inhibitor. It is intended for use in motor vehicle engine cooling systems. It has been found that the conditioning treatment of silicate protecting and alkaline conditioning is essential following the cleaning process in order to deactivate the clean metal surface and to rid the system of corrosion products not removed by water flushing. When this is followed by the recommended inhibitor in the coolant, the radiator life is greatly increased.