June - August: 11,598 miles / 497.448 gal. = 23.31 MPG
December - February: 17,775 miles / 746.172 gal. = 23.82 MPG.
Higher in the winter!
Let's examine what's going on.
1. Winter formula gas. That usually reduces mileage.
2. Winter wheels and tires compared to all-season Continental tires. That should reduce mileage in the winter.
Why am I driving more in the winter 3 months?
3. There are trips from MA to OBX in there, which I don't do in season. Long distance driving which greatly increased mileage. I also track my OBX trips. Let me subtract the MA-OBX trips from the winter data.
Looks like OBX trips, over 1,400 miles each, are skewing the data. Back in a bit ... again.