another temperature gauge question
 

Seems like a popular subject ;-) Car is a 924S, 1988 - so same dash as early 944. SO anyway here is the problem. First, after being on a run, come to a stop, I then leave engine idling. Temperature gauge will creep up to the 3/4 mark between halfway and the red, then fan will kick in and bring the gauge down to just less than half way, it will cycle like this. So what this shows to me is that the fan is capable of pulling enough air thu the radiator to get that gauge down.

Second, driving around the temperature gauge tends to 3/4 mark. Occasionally it'll drop to the 1/2 mark and operate there for a while. If i'm cruising at say 70MPH and put it in neutral, then given all the cooling air now flowing thru the radiator, i'd expect the temperature gauge to drop to approximately the same position as it does when at idle, ...but it does not.

Any ideas why? It just seems odd to me - I guess as long as the gauge never hits the red i'm okay. Coolant level is stable, i've bled the system a few time and only ever get fluid out of it when I crack open the bleed bolt. Thermostat was changed over a year ago - not that it made any difference & I can't remember what temperature rating I replaced it with - standard ? 80'C?.

Steve

added: No A/C

All I can tell you is that you must be using a fairly high temperature stat and thermal switch. The thermal switch controls the temp at which the primary fan starts. If you want the temps to be a little lower, use a lower temp thermal switch mebbe a 823.959.481D 82/77*C or even a 823.959.481 75/70*C and a lower Tstat value. Bear in mind that the third bar on an early car is 97*C. That is getting a little hot... My car doesn't drop operating temp at 70MPH or even 120+ MPH. Do you have an A/C car or not?