The cooling fan is a vital part of a vehicle cooling system. A fan is normally tested as a component in a chamber rig. But component testing of the fan does not reflect the geometry encountered in the vehicle. System performance and engine compartment air flow distribution is difficult to predict due to the strong interaction between fan and installation geometry. This investigation is an attempt to break down the problem step by step.The flowfield at fan inlet is investigated with CFD for different geometries.The fan was tested both with and without an engine mock up behind the fan to see the influence on the fan curve.The fan flow field was measured with LDA in the vehicle with a working fan. The data was evaluated by flow calculations with a streamline curvature method.