aux fan failure confirmation

[oldskewel]

Originally Posted by andrewwynn

That's some great detail! So with a working fan, rather than attempt to generate a square wave you can dial-a-temp using a potentiometer across the sensor leads. You could run in parallel just use a high enough Ω potentiometer that the effect is negligible when set high.

Fascinating :-)

Can you control the speed or it just goes max when hits the magic overheat value?

Good question, those notes are better than my memory at this point. Doing those tests, I was mainly trying to be sure the fan was bad before buying a replacement, rather than to figure out extra details. I think if the next lower temp had triggered the voltage to change, I would have noted that. Since I did not, it probably did not trigger.

Knowing how BMW likes to run these engines hot, and having a coolant thermostat, I would not be surprised if the fan just turns on at some high enough temp, and stays off below it (unless AC is on). So that's a guess.

I agree on the idea for this being an input for active fan control.

I used a TYC fan. Seems great, no problems.