2000 Intrigue - Heating up in Cold Weather

I have 2000 Intrigue - 99,000 miles.
Lately (only in stop and go driving, NOT on the highway), the temperature gauge gets up to about 3/4. (then fan kicks in and it goes down) BUT, this only happens when the temperature is below freezing (I live in Chicago.)
Today, temperature was 42, I was in stop and go and no problems. But when its cold, the gauge will invariably go to 3/4 in stop and go.
Any ideas?
(note: never been flushed, original thermostat, and never changed drive belt either.)

This sounds like it is being caused by a sticking thermostat. It is sticking when it is cold and then will open when the temp rises above freezing. Change the thermostat and the problem should go away. I would recommend that you go ahead and have the system flushed since you have to open it anyway.

My 2000 did the same thing. I found an article about how the thermostat was redesigned and needed to be replaced. I ordered one from the dealer and put it on myself. Fixed my problem. Its fairly easy to do yourself, but just be careful when removing it and try not to get the alternator soaked with anti-freeze. Its almost impossible but just be careful.

Thank you all for your help. Replaced the thermostat (flushed and refilled coolant while I was at it) and that solved the problem. Thanks again.