Cutting down fan system development costs, improving quality, and increasing fan efficiency is a challenge that is now being addressed by the engine cooling engineers. In order to attain such a compelling goal, a Virtual Prototyping approach has been adopted, mainly based on Computational Fluid Dynamics (CFD).For the development of the fans used in the engine cooling systems, CFD now plays a key role as a design tool as well as an optimization tool. Until recently, both complex geometries and low-speed aerodynamics inherent to latter systems have prevented numerical simulations to be part of the design or reblading processes. Since the advent of general purpose CFD softwares capable of adressing the issues pertinent to the engine cooling system fans, a CFD based development of a new standard fan range was initiated. This paper presents the CFD strategy adopted and the results obtained on the new fans.Both development and re-blading of fan systems have been addressed, leading to more compact and efficient fans. Re-blading an existing fan led to a fan with 80% hydraulic efficiency. A new large diameter fan has been designed exhibiting similar performances. Comparisons between numerical results and experimental data exhibited good qualitative agreement, emphasizing the key role of CFD as a reliable tool in the design process.