[Lew Ledyard]

Are you running undersized pulleys? My motor ran too hot with undersized pulleys. Not enough cooling air passing through the radiator will prevent enough coolant from being exposed to enough air. That is why folks go to great lengths (adding pusher fans, high capacity puller fans, shrowding, etc or even bigger radiators) to expose as much coolant to as much cooling air as possible.

Moving the coolant too slowly through the system will have the same effect as having insufficient air flow through the radiator: in a given amount of time, less coolant is exposed to cooling air.

The hp gains from undersized pulleys is immaterial in these cars. When I got rid of the undersized pulleys, I no longer needed a pusher fan.