The aim of this study is to investigate experimentally the heat transfer and pressure drop characteristics of a flat tube of a radiator using water based copper oxide nanofluids. The heat transfer coefficient and pressure drop were estimated for different nanofluids concentrations, inlet temperatures, Reynolds number range. The heat transfer coefficient increases with increase in particle concentration, Reynolds number, fluid inlet temperature and air inlet velocity. The enhancement in heat transfer coefficient is about 12% at Reynolds number 30000 for fixed 0.1% v/v CuO nanoparticle concentration and maximum enhancement of about 23% was observed for 0.4% v/v particle concentration. The maximum pressure drop in the vertical tube was about 1.43 times that of the base fluid at the particle volume fraction of 0.4%.. The results of this study proved that nanofluids have great potential for enhancement of heat transfer in practical applications.