Castrol Radicool is a concentrated engine coolant for use in both petrol and diesel engines with aluminium or cast iron engines. This coolant can be mixed using 33% concentration with purified water to give frost protection to -18 deg C, however it is recommended to use a 50% dilution to provide optimum corrosion protection and freeze protection down to -36 deg C. At these concentrations this coolant will provides year round protection. To maintain optimum performance this product should be replaced after 1 year