Computational analysis was performed for the external flow around an automobile and the internal flow in the engine compartment using a multi-block grid system and a finite-difference method. Cooling performance of the radiator is evaluated by the flow quantity passing through the radiator. Computational results show quite good agreement with experimental data. Present method is applied to the design of an the inter-cooler, it shows that the cooling performance of the inter-cooler could be improve by changing the duct configuration.