AkechiMotors

I came across a lot of threads about fans that won't shut off, but mine shuts off just like it should. What it is doing that I'm not so sure about is run the entire time the car is driven. Bad switch?

MAGK944

What car, 924, early 944, late 944? It makes a difference and I cannot see a car listed on your profile or signature.

AkechiMotors

Oh sorry! '89 944S2.

MAGK944

If the fans run as soon as you start a cold engine with the AC off, it likely could be the coolant temperature sensor is permanently grounded through its body or you have a bad fan relay. There are a couple of other less likely suspects if swapping those out doesn’t do it. This might help: http://www.clarks-garage.com/pdf-manual/cool-01.pdf

V2Rocket

make sure the ac snowflake switch is off.

AkechiMotors

Right - I didn't check if that was the case.

Thanks - that's very useful.

More data for anyone who might have an idea: the ambient external temperature while driving is in the 60's, and the duration of the trips is no more than a 30 minutes or so. The temp gauge displays dead-center normal. After shutting of the car, the fan runs for 60-90 secs, then shuts off as designed.

aussie944cab

Check under the intake manifold, there is a temp sensor which will turn on the fans if it's faulty or disconnected

moliver

I don't think this is true...the temp switch is screwed into the radiator.

MAGK944

Correct, iirc the sensor under the manifold is just for the guage.

sobamaflyer

evidently that temp switch (in the radiator) is a VERY common (also very cheap and not terribly hard fix) problem. But in my experience it meant the fans would run ALL the time, car off, key out.

V2Rocket

thats on some variants of 928, not 944.

aussie944cab

My 89 S2 cab has this feature, when you disconnect it the fans run all the time when the ign is on,
As far as I can figure, it's a back up safety feature in case the in-radiator temp sensor fails or if engine heatsoak is effecting air temp

aussie944cab

The guage sensor is under the manifold by the engine block, this sensor is under the main body of the plenum, in line with the alternator, it has two spade terminals
https://rennlist.com/forums/924-931-...-manifold.html
Post 12, top right hand of second picture, you can see the 2 pin sensor
https://rennlist.com/forums/924-931-...fold-swap.html

MAGK944

I have seen that switch before but I’m not convinced of the reason given for it in that post, I suspected it had something to do with emissions. If it measures intake air temperature like it says, how would switching the coolant fans on affect the air temperature in the intake? Maybe I’m missing something, a wiring diagram would confirm what it does, my knowledge of the 16v cars needs brushing up on.

aussie944cab

I've been playing about with that part of the car (installing AC) and when I started the car afterwards the fans were on from start up, found that thread in rennlist and checked and I had knocked the connectors off, put them back on and fans only come on when coolant is hot enough
Not sure about US cars but my 89 has no emission stuff, not even an O2 sensor