Hi I have a Saab 9000CSE 1993, 162,000miles 2.0L LPT
Recently I have noticed that the temperature gauge on the Dash drops from its centre position after it has fully warmed up to a slightly lower position and then again back to the middle position and this is driving in normal traffic conditions.
On the motorway the temp needle remains in the middle postion.

My understanding is this:
When u start the car from cold the engine warms up the temp gauge needle starts to go up. After driving for a while the needle increases to greater than the middle point and when the thermostat opens the needles drops to below the middle point and then rises again to settle at the middle point. From now on the needle should not go lower only higher if you are in traffic ie before the fan comes on or you have let the engine cool down after switching it off.
In my case it does the above but instead of settling and remaining in the middle its going lower and back to the middle and continues to do that until I am on the motorway where the needle stays in the middle.

I have changed the antifreeze and I have changed the thermostat 89C. But it still persists to go up and down.

What I haven't changed is the temp gauge sensor on the block itself.

I have talked to my local Saab dealer and they suggested a new thermostat which I have now done.

Any ideas of what it might be. Should I be worried

Has this happened since the cooler weather arrived? Despite having a relatively new thermostat,in winter my 9000i temp gauge varies between 1/3 of the way up and the middle, depending on how high I have the heater set, road speed, overrun down a hill etc. The cooling fan cuts in when the gauge reads 3/4. I get the feeling they are very sensitive gauges ( I've read somewhere that they are linear gauges as a pose to logrithamic? which are fitted to most other cars). This means that the needle moves directly proportionally to the change in temperature.
Hope this makes sense.
Jimbob

this is nothing to worry about,my 9000s does exact. the same...it is more obvious in winter. regards m.mcg.

most likely nothing to worry about, running cool is a good thing, cool engines have a decreaced chance of pre-detonation, and other forms of internal engine failure. i would tell you to worry if your temp did not fluctuate at all, staying cold or hot, but if its in a "green" zone, its usually ok.