[Sburn]

Originally Posted by JackandJanet

Now, the only thing that power demand does at idle is use a bit more fuel (in both cases) and, for the amount of time we're usually stopped, I doubt we'll feel much difference in the AC. So, the PCM controlled fan may win out in economy at idle and not make us too uncomfortable.

But, I don't know when the e-fan controller cuts it off as speed increases. I think it is purely temperature controlled, so it's possible the PCM controlled fan might cut off sooner, as a speed increase is seen?

There's two flavors of e-fan controllers that I know of. Simple Off/On at a preset temprature (~thermostat temp) and PWM e-fan controllers that vary the e-fan speed based on the temp. sensed at either the radiator or by piggybacking on the factory ECT/CHT. So, the e-fan with a smart controller wouldn't always have to be running at 100% when it's on.

I know there was always some power loss through the fluid clutch since it is always ON. But, could the new clutch be purely (or effectively) mechanical? I doubt the new design would have been adopted if there were no real benefits. The fluid coupled fan was "simple", and it worked, but there was always drag. Maybe the drag was eliminated in the new, more complicated design?

- Jack

I'm not yet sure how the clutch works on the new PCM fans. Could be a PWM to some kind of solenoid that squishes some hydraulic bits, or a variable DC voltage to a magnetic particle clutch. I'll have to RTFM this weekend. Or, drag out the old oscilloscope.

Ford's PID show the fan RPM sensor and PCM output to the clutch as a percentage, but I don't yet know if the percentage mean duty cycle or a voltage: