A couple of days ago, I turned on the heat in my Roadster for the first time ever (I've just been using the seat heater so far, but the wife was in the passenger seat, so…). Anyway, this morning, I noticed that the coolant level was suddenly lower than usual for the first time ever. I waited until the coolant pump stopped, and where the level has always been just below the high fill line, now there was just a tiny amount at the bottom of the reservoir. Coolant is still pumping, and the battery temp has remained cool. I can't find any sign of leaked coolant in either of the places I have been parking. Is this a coincidence, or is there an additional volume of coolant that is used for heat, or something else? I've topped up the coolant and will keep an eye on it, but thought I'd ask if anyone here has seen this before.