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Message: <blockquote data-quote="jarance" data-source="post: 601652" data-attributes="member: 21">I think it depend rather on the efficiency as well.Both electrical fan and mechanical fan required the same amount energy to produce the same amount of air flow to cool down the heat in the radiator.Electrical Cooling = Efficiency of Motor  (85% to 95% efficiency) + Efficiency of the Alternator (90% to 96% efficiency) + Loss in cable resistance.Mechanical Cooling = Efficiency of the Fluid Coupling (70 to 80%) + Loss in friction drag of clutch fan.However Load on the engine from the Alternator is variable. if the battery is weak, the slip ring will "moved" and produce more charge for the battery, this will put more load on the engine. If the battery is "fully charge", the slip ring will reduced the charge to the battery and lessen the load on the engine.Similarly, the clutch fan also does the same thing. when the engine is hot, the clutch will draw the turning force from the engine.when it is cold, it start to slip and draw less power from the engine.</blockquote>