Finally solved my over heating problem!!!

To the OP: Just keep an eye long term on those stainless steel fan blades; I have used 2 of them over the years and both had blades crack on them after a couple of years on the street. They tend to crack close to where the blades meet the center spokes.

To follow up on redness's and teringer's posts: The thing about the electric fans that is not obvious is that with the thin style fan blades, even a small amount of pressure drop into the fan inlet or pressure build-up at the fan outlet will make the through-flow drop like a rock. What happens is that with even a small pressure difference inlet-to-outlet will cause the air being pushed outward by the blade to simply flow around the blade and back to the front side of the blade. So it ends up moving the same air molecules around and around itself, instead of moving a continuous flow of air through the fan. The thinner the blades, the more this problem crops up. So a fatter blade will do much better with any pressure drop across the fan and shroud, like the blades you see on factory electric fans and stock factory metal fans.

If you look at any catalog for any fan like pictured by the OP, you can find flow numbers in the 1500-2000-3000 cfm range, but those numbers are only for a perfectly free flowing situation. As soon as you put these behind a radiator and a tight shroud, you are going to get a low pressure area behind the rad, and this circular flow around the blades will occur, and the total through-flow will drop into the toilet. This is what happens with inexpensive electric fans in a tight shroud at idle or low speed.