I had the bright idea of changing my main interior fan (the one at the rear of the engine bay) for large computer style fans from RS, the idea was to save space. Anyway, believe me, the airflow they generate when pushing through a radiator core is pittiful, these were 6.5" fans if I remember right. You could just feel a slight breeze from the air vents inside. Granted they had a little bit more work to do than what they would have to on top of an oil cooler but I genuinely dont think they are the way to go. As above, mounting the cooler in a good place with regards to air flow has to be the best way of doing it.