Are you letting car warm up longer? Even if you let car warm up for 2 minutes while you remove ice or something will significantly drop the MPG. I start my car and immediately go (summer) taking it easy while she warms up. In winter I'll start my car and go too, but if there is ice on windows I will start car then grab the scraper and remove ice then go. So that takes a couple of Min so this time idling really kills the MPG. But for the most part I see no difference. I average 32 MPG that is 6000 miles averaged. Mostly city type driving.I have been averaging 36 mpg on mix city highway driving in the summer.
After the temp dipped below 30 degrees I averaged 32 mpgs.
The last 2 days it has been below zero and I now got 25 mpgs.
Anyone else living in a colder climate??