Joined: Jun 2014
Location: The Bluegrass State
You're seeing a smaller drop than I would expect.
In winter, lots of things happen. First, fuel retailers switch to "winterized" fuel. It's got additives that help prevent freezing in your tank, but it also has less energy per liter so your fuel economy will drop. Second, the car will run in closed loop mode for a longer period of time because it takes longer to reach operating temperature. This increases fuel usage. Third, the colder temps. increase fluid friction, which robs horsepower, which increases fuel usage. Fourth, cold air is more dense, which pushes upon your car with more force, which increases fuel usage while on the highway.
It's almost impossible to get your best MPGs during winter. I typically see a 2 MPG decrease with my cars and trucks both during winter.
2003 Mach 1 - TR3650 - Ford Performance aluminum shaft - Mac O/R H-pipe - Airbox modification - 17% tint
Gone but not forgotten:
2001 GT auto in Zinc Yellow-Flowmaster mufflers - Pypes O/R H pipe-Eibach Sportline springs/Koni STR.T shocks-AMR wheels w/ 315/35 MT Street Comps-FR 3.73s-Blankenship Performance tuning-Steeda Under-drive pulleys-BBK CAI-AcuFab 70mm TB