Heat transport capacity of conventional coolants for car radiators can be enhanced by adding nano size metal oxide particles. This paper presents a three-dimensional themio-fluid analysis of real size car radiator with louvered fins and nanofluid based coolants. The base coolant consisting of 60% Ethylene glycol and 40% Water is dispersed with Aluminum oxide, Copper oxide and Zinc oxide nanoparticles. Effects of nanoparticle concentration and flow velocity on heat transfer have been reported. Dependence of thermophysical properties on nanoparticle concentration has also been evaluated. The heat transfer coefficient for coolant was increased by 42.5%, 47.4% and 51.1% on addition of 2% of Aluminum oxide, Zinc oxide and Copper oxide respectively. A Significant linear increase in heat transfer coefficient and Nusselt number was observed with rise in flow Reynolds number. Copper oxide nanoparticles based coolants are found to be more effective. A set of simplified correlations for the Nusselt number is presented. (C) 2020 Elsevier B.V. All rights reserved.