Engine temp question

Hello Saab world

I have a 2006 9-3 convertible 5 speed manual with the 2.0T... runs strong 155K. My question is this, in the summer the engine temp is in the normal range appx centered in gauge. But in the winter the gauge is at or below the first mark. Even after driving for 30 minutes. So the answer the next question... Yes I replaced the thermostat, and coolant sensor(s) and still the same. My only concern with this is the engine running rich. Maybe this car was made for the desert driving... any help would be helpful.

Thanks
Darryl Usmarine0905