It happens each and every years, my fuel consumption decrease sharply in November.
For example, my 2000 Impreza was getting 620km per tank (385milles) or 29mpg In winter, I can get about 550 km per tank (340 milles) or 26mpg
The thing is that I drive the same route at the same speed, I always monitor my fuel consumption over the same route.
Last week, I had an even more interesting expetience: I filled my tank in Quebec city and I manage to get 535 km before going on the reserve (330 milles) I did average about 23.5mpg (US gal) or 10L/100km, I below than average score, even for winter I filled up again near Ottawa and this tank gave me 645km before I went on the reserve I did average 8.7L/100km or 27mpg
It is a 13% difference.
This summer, my fuel economy never went below 27mpg unless I did major city driving and I really notiver when I do not hit 600km per tank
My guess, the Winter gas has arrived in Quebec and not in Ontario.
Charles Leblanc
2000 Impreza 2.2l 5spd