The engineering process in the development of commercial vehicles is facing more and more stringent emission regulations while at the same time the market demands for better performance but with lower fuel consumption and higher reliability. Respective targets require better utilization of existing or even higher engine cooling capacity and optimization of aerodynamic performance for reduced drag. In order to aid on achieving both goals, special attention should be paid on understanding both external and under hood flow structures.This paper describes an optimization study for reducing aerodynamic drag and increasing engine cooling performance conducted on a Light Truck at Jiangling Motors Corporation (JMC). The approach is using simulation based on a LBM solver coupled with a heat exchanger model. Such methodology was used to predict both aerodynamic and cooling characteristics and help highlighting potential areas for improvement. These results where then directly suited to appropriately modify or design devices to significantly improve performance while keeping the design changes to a minimum. The predicted improvement to both cooling and aerodynamic performance were in a last step confirmed by evaluating fuel consumption and radiator top tank temperature under critical operating conditions in driving tests. In particular, the reduction of aerodynamic drag by more than 14% translated into a reduction in fuel consumption by 2.1 liter per 100 km.The above results are discussed in the context of using a simulation approach as an effective optimization tool in the development process and as a means to not only complement physical test but reduce the amount of physical testing. Such processes are needed for complying with today's and future cooling and aerodynamic challenges at reduced development cost as well as development time.