The Wuling Rongguang is a small van which uses a mid-engine layout where the engine is located underneath the floor panel in-between front and rear wheels. A particular challenge for this kind of layout is the protection of the engine against soiling. Typical protective measures consist of large mudguards in combination with an engine cover. While needed for soiling protection, these parts can have a strongly adverse effect on aerodynamic drag.This paper describes process and the results of the aerodynamic optimization of the underbody of the Wuling Rongguang. Because design changes had to be evaluated for aerodynamics performance as well as for their effect on the soiling, a digital approach was used which allowed to do the soiling analysis as a post processing to the flow simulation. As a first step, a baseline model was built and analyzed. This included the development of a soiling model taking into account wheel spray and splashing effects. The soiling model used available best practices where available and was also calibrated against some road test results to ensure a proper reproduction of the soiling effect.The analysis of the baseline results identified the areas of inefficiencies and the potential for reducing the drag. In an iterative process design changes were made to the front mudguards and the engine cover to improve the flow in the underbody and finally to the rear spoiler for improving the overall wake structure. The soiling performance was evaluated for all design changes and only those changes that gave improved or at least equal soiling patterns compared to the baseline were accepted. As a result of this process, an overall improvement potential of 9.6% in aerodynamic drag was obtained.The final step in this project was the confirmation of the results in the wind tunnels of the Shanghai Automotive Wind Tunnel Center (SAWTC). The tests in the aero-acoustic wind tunnel confirmed an improvement of 7.1 % for drag. Tests for soiling were done in the climatic wind tunnel. These tests in a well-controlled environment also confirmed the results obtained from the CFD simulations.