With the demand for the improvement in automobile engines efficiency, engine cooling system is one of the areas of improvement. A radiator is a key component of the cooling system, which maintains the temperature of engine parts within the optimum limits. In this work, the three-dimensional fluid flow and heat transfer characteristics through a cross flow type automobile radiator is analyzed numerically. The coolant from the engine passes through the radiator tubes axially which is cooled with the help of atmospheric air entering in the transverse direction. The flow field through the coolant domain, air domain and solid tubes are obtained numerically by solving the continuity, momentum along the three directions and energy governing equations using finite volume discretization. The heat transfer characteristics and efficiency of the radiator can be improved by increasing the surface area of the tubes within the same overall dimension and hence a numerical study has been carried out by varying the cross section of the tubes from tubular to rectangular with semi circular ends through which the coolant flows using CFD code ANSYS FLUENT 12.0. The geometry and mesh generation has been carried out using ICEM CFD and TGRID respectively. The study aims at decreasing the coolant temperature from 6 degree to 10 degree at the outlet of the radiator. The initial analysis of the radiator with tubular cross section is analyzed and validated with the experimental data of a TATA INDIGO automobile radiator fromliterature. The study also aims at optimizing the mass flow rate of coolant in achieving the required drop in coolant temperature. The temperature at the exit, pressure drop across the radiator tube, wall temperature and velocity along the mid plane are plotted. © Research India Publications.