[Diesel_Dave]

Thanks for the info, slowmover. Here's what I'm thinking: if the fan runs eccessively as it's currently set up (which I have yet to determine), I might be able to make a kill switch for the fan. That is, make a switch so that switch off = fan off, switch on = normal fan controlled by ECM. That way, when I know I'm not going to need the fan I can just diable it with the switch, but when I think I might actually need it I'll let the ECM control it as it normally would.

The advantage here comes from the fact that I know what I'm about to do even though the ECM doesn't. It has to control the fan assuming that at the next moment, I'm about to to the worst case scenario. For example, if it's a cold morning and I know I'm going to start, go 2 mi and hit the highway I could probably turn the fan off completely to warm the engine up faster, knowing that I'm going to be plenty cool enough when I get up to highway speed. The ECM control strategy, however, has to be prepared in case I was towing a heavy load and was going to be doing slow stop & go for a long time.

From a FE standpoint a clutched mechanical fan is superior to a pure electric fan because you don't have all the losses associated with the alternater converting mechanical power to electrical power and then an electrical motor converting electrical back to mechanical. I could see why folks might want a pure electrical fan to get more power out of the engine. If that's your goal, for a short period of time you can afford to drain the battery down and the alternator doesn't need to keep up. But for FE, I'm thinking why bother spending the money on an electric fan conversion when I can get a better FE solution with just a fan kill switch.