I thought I'd resurrect this to report an incident this morning on the way to work.
I leave my DIC set on temp after finding that I had an over heat situation in temperatures just above freezing while traveling at speed on the highway.
This morning, I fired up and turned the defroster on to clear the windows. As always, git good heat quite quickly. Then, part way to work, the heater (which was by then directed at my feet) suddenly started putting out cold air and the coolant temp climbed to 238 deg. quite quickly. This was probably because the thermostat had just opened, but could also be independent of that. I turned the heater off and was about to pull over, when the temp started falling again, so I once again turned the heater on full and got hot air again.
Frankly, designing a car with a defect like this is BS.
I first observed the high temp situation (though not that high the first time) with a car that was almost brand new and had never been touched as far as coolant system. When I had the high reading, I took it in on warranty to have it flushed and topped. They treated me like they were doing it to calm a panicking customer, not because there was any actual problem.
Small Dealer had indicated that there was a fix for heater involvement which is why I tried turning it off. Perhaps this fix would address my problem. Has this fix - valves? - been released and is there a bulletin one can quote to the dealer?