Mechanical Fan VS Electric Fan

67Baccaruda said
I have never been able to get my brain around this. The relationship between mass and power being linear. If you move X mass of air with a mechanical fan, and X mass with an electromechanical fan. the power required to move the mass (rotating force to rotate the fan blades) should be identical. Belt turning fan or belt turning an alternator. Actually the electric fan should be a little less efficient, with losses in the alternator and resistance in the low voltage wiring, 2 sets of bearings vs. 1 etc... Some one help me out here.

Mass and power relationship may be linear but many other factors are not. An electric fan spins at a constant speed independent of engine RPM whereas a mechanical fan has to turn X revolutions per RPM. The mass of the fan, clutch, belt and pulley have to be accelerated with the engine which is what robs HP. If your cooling system is sized correctly, most of the time you don't need a fan if you're going over 30 mph and even at a idle, a thermostatically controlled electric fan will operate only when it's needed.