Originally Posted By: bunnspecial
My one car with a mechanical cooling fan has it directly attached to the water pump(via a V-belt that also drives the alternator). There is no clutch.
I've considered installing electric fans. To my way of thinking, there two deficiencies in mechanical fans that aren't present in electric fans:
1. In stop and go traffic, the fan is moving fairly slowly and there's virtually no ram air to help it. On warm days, I watch my temperature gauge creep up, although admittedly the car has never overheated.
2. Going 70mph on open road, the engine is getting a lot of ram air. While it's probably not enough to cool the engine on its own, the mechanical fan is spinning far faster than needed. I think the water pump pulley and harmonic balancer are about the same diameter, which means that on the fan is turning at the same speed as the engine. At 4K(~70mph) that translates into a lot of wasted power along with a tendency to overcool the engine.
Later models of the same car had dual electric fans(NA) or single(rest of the world). The system was fairly primitive as the fans where controlled by a simple on/off switch that activated around 180ºF and the fans only had one speed. None the less, it helped in the two situations I describe above. My car can't be readily adapted to take the factory type electric fans(they moved the radiator support closer to the engine since it didn't have to clear the engine fan and they needed the space for the fans up front. There are aftermarket kits.
Ram air is usually sufficient to keep an engine cool, unless towing, or driving slow. at 40 MPH you're pushing around 200 cfm through that rad (4ft² surface)