[divezic]

Z-Man,

I hate to mention this but I think your mechanic does not know what he is talking about. There is nothing in the cooling system that takes and "air inlet" reference temperature. That is solely a fuel injection sensor on the air flow meter.

If your fan is cycling very often at slow speeds/idle and not at faster speeds, I can think of three things:

1-Partialy clogged radiator OR a failing water pump. Don't be alarmed yet. I don't think there are the problems because you'd probably get the same indications when running high speeds, especially during DE.

2-Air bubbles in your coolong system. These cars are very sensitive to air in the system and they are a pain to bleed properly. You mentioned that you had a lower temp fan switch put in your radiator. Who did it and is it possible they did not bleed the system properly (like the guy who diagnosed a cooling problem related to a FI component?) On a 944 NA it isn't difficult after you get a good technique to do it. Ya just gotta do it right.

3-I think this is most likely the problem. New lower temp fan switch will kick the fan on around the 1/2 tick mark (OEM switch kicks it on around the 3/4 tick mark). OEM thermostat keeps the coolant around 90 C, which roughly correlates to an engine temp around the middle tick mark or a little lower. So if the old thermostat tries to keep the engine temp little less than 1/2 and the thrmo fan switch kicks the fan on at 1/2 then it takes very little time at idle (aka no air cooling flow) to cycle the fans. I believe that your system components are working perfectly, but not working together properly. If this were my car I'd change the thermostat to a lower temp unit (80 C). This will keep the engine temp at about the 1/4 tick mark or a little less. You will find that your fans cycle less but when the fan is on it will stay on for a little longer than before.

Please note that I have a 1984 944. The temp gague markings are probably different, but the function of the cooling system is the same. The gague had 5 tick marks. I call them: low, 1/4, 1/2, 3/4, and blow your engine up. My car has a lower temp thermostat and an OEM fan switch. When driving, my car always remains at the 1/4 mark and the fan kicks on at the 3/4 mark when in traffic.

The fact you mention that your temp always stays steady reinforces my theory. There is a very little temp spread between the thermostat and the fan switch. Hence the quick cycling and the steady temp. Furthermore, there is no cycling at speed because there is enough cooling air flow to keep the temp out of the fan switch range.

Good luck and keep us informed about your progress.