Advancement in cooling systems being a greater criterion for their remarkable improvement in the performance of automotive, radiator plays an important role in this aspect. By using an effective coolant, a better heat transfer rate can be achieved in the radiator. Small concentrations of nanoparticles, having superior thermo-physical properties, suspended in a base fluid can bring out better rate of heat transfer than that of water/water and glycol mixture alone. An elemental part model of the radiator is considered for the present study. The coolant comprises of a suspension of carboxyl graphene nanoparticles in water and ethylene glycol as base fluid. CFD simulations are carried out for different air, coolant mass flow rates at different volume concentrations of nanoparticles and coolant inlet temperatures. It is observed that effectiveness decreases and pressure drop increases with increase in the mass flow rate of the nanofluid. Maximum of 18.32% increase in effectiveness is achieved for coolant mass flow rate of 0.2778 kg/s and coolant inlet temperature of 323K at 2% volume concentration. The enhanced heat transfer rate due to the use of nanoparticles gives rise to a high performance to weight ratio, thereby making it possible to significantly reduce the size of the radiator and making it much more compact.