Amateur Radio club (NARC) had an event to monitor - a Running Room "Hypothermic" half marathon. So with ambient temps hovering all morning at -17C (just above 0F) I left Pearl "ON" and sat inside most of the time - for three hours. When running at idle Pearl consumes about 0.8 l/hr. My MFD mileage started out at 5.8 l/100 km and after the three hours read 7.8. Pearl cycled the ICE constantly maintaining an interior temp of 21C all morning. Coolant temp varied between about 65C and 50C. All numbers taken off the Scangauge II. So much for my long term mileage. Best male time for the run was 1hr 20 min and best female time was 1 hr 40 min. Last runners clocked in at around 3 hrs. When you run outside in these kinds of temps there is no danger of "freezing your lungs". You do, however, have to manage your moisture loss, making sure you aren't wearing too much clothing (you get wet) or too little (you could suffer from frostbite). Most runners had frost buildup on their faces and heads. Many were wearing light head balaclavas. They were black, and covered with frost at the finish. One particularly large female (over 6 foot tall) did a hand flip in front of the finish line (celebrating her 1 hr 45 min time)! VERY impressive!!
0.8 L/hr @ -17oC is a great data point. Hope somebody is writing these down That gives about 50 hrs max starting with full fuel? It may be that your 'call for cabin heat' led to a higher ICE duty cycle than would have been required just for engine coolant or SOC holding. Not suggesting that you should sit there w/o cabin heat though. I wouldn't.
Good to know. If a Prius driver should happen to be stranded during a blizzard, that is a good survival space. A lot of conventional vehicles would run out of gas quickly That alone is why I *always* top-off in winter when my tank is around 3/4
