AND dont forget the fan blade has the opposite blade pitch. I made the mistake once when I converted a truck to serpentine. It cooled great at idle but, at 40 mph, it got hot. At 70mph it was cool. Finally, standing in front of the truck, I noticed that the air was blowing towards the grille!!!! Duh. At idle, the air still went across the radiator. At 40, the air coming in the grille cancelled the air being blown forward by the fan. At 70, the incoming air overcame the fan clutch. Took two days to figure it out.

mike in tucson