Originally Posted by kellyfj10
It could also be the additives that they put in the gas in the winter. I know that in the winter I get 2-2.5 mpg less then in the summer. Also could be the colder air. The engines like cooler air 60 degrees and up but they don't like freezing air. At least that is what I have been told.
That is correct that you will worse fuel economy in the winter due to the winter grade fuel. Longer warm-ups will also affect your overall fuel economy.
Cooler air = more dense air which = more power which won't decrease your fuel economy.