Testing TT Temp Gauge
 

If you are having problems with your temp gauge, there is a way to determine the actual coolant temp, which you can then compare with the gauge:

To get a digital coolant temp reading, on the climate control panel, hold down at the same time the 'recirculate' button and the 'up' arrow (it's the one on the upper right corner of the climate control panel). '1C' will come up on the display. (This may take several tries, try pressing the "recirc" button a tiny bit before the up arrow.) When you get 1C, turn the temperature setting dial to the right until code '49' is displayed. This is the coolant temperature reading, then press the recirculate button again, this time by itself, to get a temperature reading. It will read in degrees Celsius.

I found that the digital read-out shows the coolant temp fluctuating between 77 and 82 degrees C, whereas the gauge fluctuates about 20 degrees, between 70 and 90. At any rate, I am now confident that the car is not overheating or over-cooling.
Happy Holidays everyone!