I doubt it’s the thermostat. When the thermostat fails it’s generally shows a temp too low or gives the (- - - - ) reading in the DIC.
Since he just went to the oil change place, I would check their work. Probably opened the radiator cap to check coolant and introduced an air bubble.
I would suggest burping the cooling system.

 

"always 206F" leads me towards the cooling fan as a possibility. Maybe a clogged or obstructed radiator or just low coolant level. Or, somebody thought a 190 t-stat was better than 180.
While 206-216 is not over heating it is a bit on the high side. Don't use anything other than AC-Delco 131-158 t-stat. The purpose of a t-stat is to keep the coolant ABOVE 180F.

Coolant level should be checked under the pressure cap, not the recovery bottle.

 

And to add to those great suggestions, change the Dexcool every 5 years, refill with 50/50 Dexcool.and burp the cooling system

 

Maybe not the most common defect, but it is possible for a thermostat to open just fine, but at a temp that’s too high. That would explain the “always 206.” What else would?

Good advice. Makes sense to me.

There really is no other plausible explanation for a system that’s “always 206” (if true) than a defective thermostat. With a properly functioning thermostat, with the car at cruising, the temp would be close to the set point, no fan needed.. A clogged system would cause erratic readings.

Oh, wait! There is another plausible explanation! I suppose a defective temperature sensor could be sending bad information.