The cooling system of a car engine effects strongly the efficiency of the car engine so many studies were presented to enhance the cooling system of the car. The components of the cooling system are radiator, water pumps, fan, shutters, thermostats, expansion tanks/storage tanks, water pipes, water temperature gauges, etc. Among these components, the radiator considers the primary key to enhancing the efficiency of the car engine. Many studies were achieved to enhance the efficiency of car radiators by using different nanofluids as a coolant are discussed in this literature review study. These previous studies investigated various kinds of nanofluids such as Al2O3, CuO, TiO2, SiO2, and ZnO with different base fluids. Nanofluid concentrations, nanofluid temperature, and nanofluid flow rate were studied by previous studies eleven years ago.