Oh, and I was still offered no reason as to why the temperature reading on the dash was going haywire. It's amazing that it's fixed, although nothing was replaced.
So they took the air out of the system (if there was air in there). Where did the air come from? Why was there air in there? What, if anything, was wrong with the thermostat? How about the sensor?
With none of the above questions answered, it still got fixed. Amazing.