[aerohead]

In 1974,when CAR and DRIVER aero-modded their Ford PINTO, the 4-blade,fixed-blade fan was removed and they gained 1-mpg @ 70-mph.
There were no electric fans in the day,and they needed some cooling,so they converted the fan to a fixed,2-blade unit and figured that they gained 1/2-mpg @ 70-mph.
Later,flex-fans came out which deformed centrifugally,which unloaded the engine at high speeds,where a fan was unnecessary.
Thermal,viscous-drive fans WERE in existence at the time,and theoretically,at speed,would be completely unloaded unless under strenuous circumstances.
With stringent CAFE standards now,carmakers are going to computer-controlled electric water pumps,split-flow cooling systems,electric cooling fans,and computer-controlled radiator blocks.
ISUZU has even eliminated the radiator with their 'GLIDER',Class-8 tractor.
I think that the days of the belt-driven fan are numbered.