Agree to disagree on that. 🙂

 In the real world, once the t-stat opens, it stays open as long as the engine is running. In my experience, if the cooling system is full(no air), has the proper coolant, air flow thru a clean(ish) rad, and an operating t-stat, the engine temp will pretty much stay the same once it gets to operating temp. The t-stat cannot open any more than full once the engine temp gets to the rated opening temp of the t-stat. In the time that it takes the t-stat to open, engine temps have already passed the rated opening of the stat, and therefore the stat will remain open.
A 165 deg stat will open at a lower temp than a 185 deg stat. If the engine remains running, the running temp will keep rising...the t-stat will not make it run any cooler....it's fully opened. The only thing that keeps temps in check at that point is air flow thru, and coolant flow in, the radiator. Idling in traffic will cause engine temp to rise, but the fan keeps air flowing enough to keep from overheating. Once moving again, air flow thru the rad will cool it back down. I can't see any scenario where the engine temp, once running, will cool itself back down enough to close the t-stat, even in extremely cold ambient temps.

In this particular case, I would be suspicious of  faulty temp sending unit, or gauge(or both), since measured temp at the upper radiator NECK was 180deg. The rad metal can't be at 180 if the coolant is only 165...right? 🙂

If you have a 165° thermostat and it opens at 165⁰ then what happens to keep the engine temperature from reaching 150° on a 30° day? Are you saying that the thermostat is either fully open or fully closed around the stated temperature?

Also in my example of a thermostat that was barely cracked open and the car would never reach operating temperature.

The way I understood it was that the wax in the pellet of the thermostat would expand and contract thereby controlling the temperature by modulating the flow through the radiator but it wouldn't be one or the other as the temperature changed.

Hi, As long as we are on "Cooling" subject, Are the foam rubber radiator gaskets on the support really needed? For a mild drive and mild mannered engine, do they really aid in cooling enough to merit them being installed? 

On a hot day, on the highway with the A/C on, they definitely help, especially with a big block.  YMMV