judoflip

Daily high temperature has fallen below 50F in my neck of the woods, sub-freezing for lows, and I've noticed a -3 MPG reduction in average fuel efficiency for the month compared to summer and fall. Granted, I'm running the heater and defroster/AC almost constantly, and the seat and wheel warmer some of the time, but I didn't think colder temperatures would make that much of a difference.

Is this typical?

Chris8152

Yes it will make a difference as your engine will be running more in the cooler weather.
Try using the heated seats as much as possible until the engine reaches normal running temperature before using the heater, this should help, unless like me you only do 6/7 mile trips then the engine hardly gets a chance to get to normal running temperature and this is why I think I get such a big difference in mpg in cold and warm/hot weather.
At the moment in the UK its 36F and my average is 26.
In the summer at around 65F + it goes up to a average of 32

Modeler

It would not make a difference. This car is smart: the heater will not kick in until the engine is sufficiently warm.

As you have pointed out, the difference in the MPG is due to the need for the engine to warm up every time you make a trip after the car has been sitting for awhile. The more trips you make during the day, the worse the mileage will be.

zc1

I just finished an 800+ km (500+ mile) trip in the GSh. Average temperature was -6 degrees Celsius (21 F). 98% highway miles. I averaged 7.9 L/100km, which works out to 29.8 US MPG and 35.8 Imperial MPG. At -5C, this has been an unusually warm weekend; temps had generally been around -20C (-4F).

Overall, with my driving being about 50% city and 50% highway in winter driving, my mileage is 8.2 L/100km (28.7 US MPG or 34.4 Imp MPG). This has been entirely winter driving, again, with the average temperature around -20C/-4F. I'm very happy with this, and expect it to get better once the weather warms up.