The cooling system of a car plays an important role in vehicle's performance, consists of two main parts, known as radiator and fan. Improving thermal efficiency of engine leads to increase the engine's performance, decline the fuel consumption and decrease the pollution emissions. This study presents an experimental study on enhancement of heat transfer in car radiator by using aluminum, copper and distilled water nanofluids. The range of nanoparticles concentrations used were in the range of (15 – 35 wt %). Two nanoparticles aluminum (Al (50nm)) and cupper (Cu (30nm)) used in this study and distilled water was used as base fluid (distilled water). The coefficient of heat transfer was studied with the effect of many parameters such as inlet temperature of nanofluid, Reynolds number, nanofluid concentration and types of nanoparticle.. Results show that Nusselt number increased with increasing of nanofluid inlet temperature, nanoparticle volume fraction and Reynolds number.The obtained results indicated that the enhancement in heat transfer for the nanofluid (Cu(30nm) + Dw) was greater than nanofluid (Al(50nm) + Dw) due to nanoparticles size and thermal conductivity of the cupper. The results indicated that using nanofluid as working fluid leads to higher heat transfer performance which is promoted the car engine performance and would reduce fuel consumption. Furthermore, Thermal conductivity for the nanofluids (Cu + Dw) was greater than nanofluids (Al + Dw) due to nanoparticles size and thermal conductivity for the cupper. It was indicated that the type and size of nanoparticle play an important role in enhancement of heat transfer rate.