I've had my 04 SS since July and normally on my 80 trip to and from work the temp gauge would be anywhere from the width of the need from the left or right of straight up depending on if I was cruising down the highway or stuck in traffic. Now that the temps have dropped out I expected it to run a little cooler but I'm not sure if what I'm seeing is normal.

Seems to take it's time getting up to temperature. It's been in the mid 50's to 70 at 5am when I leave for work and for the past couple of weeks after about 8-10 miles it gets up to about halfway to standing straight up. After another 10 miles it gets up to as high as about 2 marks away from straight up but no higher.

Is this typical behavior for these cars so should I look at replacing the thermostat?

The car runs great and is still getting 27-28mpg on the highway so if it's not broke I'm not going to fix it.

 

That's normal... as the Miles and age of the cooling system start catching up...Naturally the temp gauge is going to waiver... But normal operating temp is controlled by what temp thermostat is in it... The gauge...is just what its named... a gauge..its not totally accurate..its there just to give you some idea what temp its operateing at... Mine to even after 14yrs...reacts the very same way.... As long as it doesn't deviate from what your already experiencing... I'm sure its fine.... If you have any doubts... keep a physical eye on the amount of fluid in the system. as long as it isn't looseing any...you should be fine....

On the other hand....

Whens the last time you did a fluid/flush of the cooling system? Maybe it over due?
Something to consider.