A new concept for an efficient radiator-cooling system is presented for reducing the size or increasing the cooling capacity of vehicle coolant radiators. Under certain conditions, the system employs active evaporative cooling in addition to conventional finned air cooling. In this regard, it is a hybrid radiator-cooling system comprised of the combination of conventional air-side finned surface cooling and active evaporative water cooling. The air-side finned surface is sized to transfer required heat under all driving conditions except for the most severe. In the later case, evaporative cooling is used in addition to the conventional air-side finned surface cooling. Together the two systems transfer the required heat under all driving conditions. However, under most driving conditions, only the air-side finned surface cooling is required. Consequently, the finned surface may be smaller than in conventional radiators that utilize air-side finned surface cooling exclusively. Results of this study include details of the hybrid system as well as radiator size and evaporative cooling loads at various evaporation rates. It is shown that a hybrid radiator with a 76-L/hr (20-gal/hr) water flow rate can transfer up to 19% more heat than a conventional radiator with the same finned area, or alternately, it can transfer heat at the same rate with a radiator size of 21% less than that of a conventional radiator.