Using ScanGaugeII, what I find is the following. The bottom edge of the "blue" part of the temperature gauge corresponds to a water temperature of 35 degrees C. The top edge of the "blue" part corresponds to 45 degrees C. With ECO switched "on," the heater blower doesn't start up until the water temperature reaches 47 degrees C. The temperature gauge reaches its "normal" operating position (1 tick mark below half-way) at a water temperature of 60 degrees C, and doesn't rise higher unless the water temperature becomes dangerously high. With the ICE "off," the water temperature quickly falls in winter because of occupant heating demand. [Don't forget that the thermostatic valve that connects the engine to the car's radiator only opens above 82 degrees C nominally, so that, for in-town winter driving, the thermostat remains closed. It's only the smaller mass of water in the engine and heater radiator core that is hot. Its thermal capacity is smaller, so the water temperature drops more rapidly in winter when the ICE is "off."] When the water temperature drops below 53 degrees C, the ICE starts up again to re-heat the water; it shuts off again when the temperature reaches 57 degrees C. It will continually cycle "on" and "off" to maintain the water temperature in this range to satisfy the occupants' heating demands. These numbers are quite consistent from day to day in my experience.

Stan