This study deals with the theoretical enhancement of thermal performance using water-based (50/50) volume fraction of Fe 2 O 3 , CuO, TiO 2 , Ag, Cu in Al 2 O 3 hybrid nanofluids as coolants for a louvered fin automobile radiator. The effects on thermophysical properties and various performance parameters, i.e., heat transfer, effectiveness, and pumping power of hybrid nanofluids have been compared with water. Among all studied hybrid nanofluids, Al 2 O 3 -Ag/water hybrid nanofluid has higher effectiveness, heat transfer rate, pumping power, and pressure drop of 0.8%, 3%, 6%, and 5.6%, respectively, as compared to water and is followed by (50/50) volume fraction of Cu, CuO, Fe 2 O 3 , TiO 2 hybrid nanofluids as radiator coolant. For the same radiator size and heat transfer rate, coolant flow rate and pumping work decreases by 3%, 4%, respectively, for Al 2 O 3 -Ag/water hybrid nanofluid and for the same coolant flow rate and heat transfer rate the radiator size decreases by 3% and pumping power increases by 3.4% for Al 2 O 3 -Ag/water hybrid nanofluid as compared to water. Reduction in radiator size may lead to a reduction in radiator cost, engine fuel consumption, and environmental benefit. C⃝ 2016 Wiley Periodicals, Inc. Heat Trans Asian Res, 46 (7): 978-995, 2017; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj).