When do both cooling fans run?
 

my 968 regularly has one of the two cooling fans on, but rarely both. seems wrong. Hows it supposed to work?

Second fan will run:

1. When the AC is on, or
2. When the upper temp is reached by the coolant temp sensor on the radiator, or
3. When the AC high-pressure sensor by the dryer is activated.

Thanks!

Just adding on to 9FF
or,
4. When you have a bad thermo fan switch. (on the radiator).

If you need help, I'm in the area.

+1

When I turn off my 84 the drivers fan funs slowly for a while.

Is there any timer associated with this so the fan doesn’t run out the battery?

I have seen it keep running for a couple of hours which seems excessive. I believe someone installed a lower temp radiator thermoswitch which is a factor but seems like there should be a feature that will turn them off eventually.

The coolant temperature sensor in your radiator is bust, it’s supposed to tell the fan relay to turn the fan off when the engine cools, usually a few minutes at most.

Thanks a lot. My low speed fan ran for 24 hours and drained my battery. I guess you are right and switch is frozen in closed position.

I will have a new switch soon. Any tricks to remove/replace? Is it easier to go from the top or from the bottom?

Top. Don't over tighten it as the plastic end tank may crack.

The switch is on the radiator and easy to get at from the top. On an na I think you just need to remove the air box and use a deep socket and short extension. You’ll lose some coolant, not much, just have some rags handy and the new sensor ready to swap in.

Thanks for the tips. I was able to get to the switch after removing the airbox and was able to work around the coolant hoses.

Old switch was a Wahler low temp that was probably 7 years old, per previous owner records. I replaced with a higher temp switch. The low temp switch had the fans funning almost constantly. It would really drive me nuts in the winter when I would drive around the block in 30 degree temps and the fans would come on as I pull into my garage.

Don't forget that your coolant temp switch is matched to your coolant thermostat. A 71 thermo uses a 75 switch and a 80 thermo uses an 85 switch, but i guess as long as the switch is higher than the thermostat then all should be good. Just don't go fitting an 80 degree thermostat with 75 degree switch.

FWIW, my pass side fan is blowing fuses. I have a replacement fan in the garage, going to swap it in today. Don't forget to check fuses, folks.

Swapped out fan. Engine stays much cooler now. (Imagine that!) Anyway just closing the loop for others who might be dealing with fan issues!