[Sburn]

Originally Posted by JackandJanet

Sburn - you're an absolute goldmine of knowledge! (I'm being quite sincere when I say that).

Thank you. I claim no special abilities other than I enjoy reading wiring diagrams and powertrain manuals and such.

Funny, isn't it, that something as simple as a temperature induced viscosity increaser would have to be replaced by sensors, specialized circuitry in the PCM and probably, a much more complicated clutch mechanism in the fan hub. I suppose that's progress, and I'm sure it's ever so much more precise, but still....

- Jack

I can make a guess why Ford ended up with such an elaborate system: R-134 refrigerant in the A/C just doesn't work as good as the older R-12 at idle/slow speeds, so you really need the fan to be engaged and pulling fresh air through the condenser when the vehicle is moving slowly. But, at highway speeds, the fan doesn't even need to be there at all to provide A/C and engine cooling and becomes a load that hurts mileage. Being that the PCM already knows the vehicle speed, ambient temp, A/C status, engine temp, etc. anyway, it makes sense to spend a few extra bucks for some wires, connectors, and a few lines of CPU code to eliminate the above two issues. And since it's all just softwre at that point, might as well do something smarter than just On/Off controll and have the PCM map the perfect fan RPM against temps, A/C, VSS, engine temps, etc.. And after replacing one or two of the older visco/thermo -style clutches in my time, I can see how having the PCM know about a misbehaving clutch would be a good thing.