Makeshift experiment: pick 2 days in a row with same morning temperature. Test #1, start car, leave garage as usual. Test #2, park car outside overnight or open garage door maybe an hour before starting the car.My Mazda is at the dealer for the past 2 days with my list of issues, including (again) the engine temperature.
I don't know details but I've seen on MyMazda that my tire pressures reset and that they put 4 miles on it so hopefully they are doing some testing there.
Btw, not sure how related it is but for me, the issue seems to have happened (or I've started noticing) since I moved and Mazda sits in garage at 55-60F (12-15C) even if outside is 25-40F; I start the car in the garage at 50-60F and seconds later the car is put in a different temperature range; if there's such a thing as ECU adaptation taking place, it could be that this change in temperature that my car gets at start-up might confuse the algorithm (unless was accounted for).
The engine bay is probably even warmer than my garage during daily-drives as this is the garage temperature when I bring the car in (garage heats up from the heat while engine cools down).
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If the ECU is the one that is commanding these values, it would make sense than why no fault code.
If there's a significant or noticeable difference in reaching OT, your garage theory will be sounding legit.