Nanofluids are suspensions of metallic or nonmetallic nanopowders in base liquid and can be employed to increase heat transfer rate at various applications. In the present study, forced convective heat transfer in an Al2O3/water nanofluid has experimentally been compared to that of pure water in automobile radiator. Five different concentrations of nanofluids in the range of 0–1.0 vol. % have been prepared by the addition of Al2O3 nanoparticles into the water. The test fluid flows through the automobile radiator consisted of 33 vertical tubes with elliptical cross section and air makes a cross flow inside the tube bank with constant speed. The test fluid flow rate has been changed in the range of 3 l/min to 8 l/min to have fully turbulent regime. Obtained results demonstrate that increasing the fluid circulating rate can improve the heat transfer performance. The application of the nanofluid with low concentration can enhance heat transfer efficiency up to 40–45% in comparison with pure water. The increase in heat transfer coefficient due to presence of nanoparticles is higher than the prediction of single phase heat transfer Dittus Boelter correlation used with nanofluid properties. These results can be implemented to optimize the size of an automobile radiator.