What also matters here is whether the fan is able to draw air from the hot side of the radiators or oil coolers rather than from the cool intake air. I installed a powerful Ferrari fan, and all it did was suck hot cowl air into the plenum through the oil coolers. Ground cooling was better when I took the fan out :(
John

Al Gietzen wrote:

 

 Al,

I believe Rino said he had a fan on the oil cooler, which I feel would be restrictive in aviation use, from what I've heard. Might be good for taxiing etc.

George ( down under)

 

George;

 

I added a fan behind the coolant radiator; and found it had no detrimental effect in flight, and made a big improvement in cooling on the ground.  This is on a pusher (Velocity) with a ram scoop.  I expect it could make a difference depending on what type of fan and the effectiveness of the intake scoop.

 

Al G