Castrol Radicool Green Concentrate 5L Castrol Radicool is an engine coolant concentrate for year-round use in both petrol and diesel vehicles with aluminium or cast iron engines. This coolant can be diluted to 33 vol% concentration with purified water to give freeze protection down to -18°C, or at a 50 vol% dilution to provide freeze protection down to -36°C if required. Castrol Radicool is compatible with all materials normally used in automotive cooling systems including hoses, gaskets, seals, plastics and all metal components. It may be used in a variety of vehicles including passenger cars, SUVs and light commercial vehicles. When top up of the cooling system is necessary, add only Castrol Radicool concentrate mixed with demineralised water at the recommended concentration (or alternatively use Castrol Radicool Premix). For improved anti-boil and freeze protection, dilute Radicool concentrate at 50 vol%.