Stringent emission norms introduced by the legislators over the decades has forced automotive manufacturers to improve the fuel economy and emission levels of their engines continuously. Therefore, the emission levels of modern engines are significantly lower than pre-1990 engines. However, the improvement in fuel economy is marginal when compared to that of emission levels. For example, approximately 30% of total energy in the fuel is being wasted through the cooling systems in the modern engines. Therefore, thermal management systems are being developed to reduce these losses and offer new opportunities for improving the fuel economy of the vehicles. One of the new emerging technologies for thermal management is the use of nanofluids as coolant. Nanofluids are a mixture of nano-sized particles added to a base fluid to improve its thermal characteristics. In this project four nanofluids; Al2O3 in water, CuO in Water, Al2O3 in 60:40 ethylene glycol and CuO in 60:40 ethylene glycol with different concentrations and particle size combinations were studied. Their thermal properties were modelled and validated against experimental data from literature. Using a numerical model these nanofluids and typical coolant fluids were analysed in a 1.6 litre, Gasoline Direct injected, spark ignition engine. This model is able to reproduce the real warm up characteristics of the engine at different operating conditions. The estimated thermal properties of the nanofluids agree with the published literature. The thermal conductivity increases with the concentration and temperature and decreases with the particle diameter, and the dynamic viscosity increases with the concentration. These findings enabled us to choose the best coolant for a system and define a proper thermal management strategy. A reduction of 17% in the total warming time was achieved for the use of nanofluids. This report also includes recommendations for further study.