After looking at the pic., it looks to me that the aluminum cover/mount you are using to mount your elect. fan could be limiting the amount of air flow across the useable radiator cooling cores. I say that because even with the holes cut in the mount you are still blocking the path of the air. I would try a full size shroud and a manual clutch fan. The standard shrouds have a funnel effect to direct the air to the fan which allows all of the surface area of the coils to have a smooth air flow across them to the fan, not just a small center area. Good Luck and keep us posted.