Fuel Economy

I track the mileage of my little commuter car with a phone app.

The app is called FillUp, and is located HERE


Below is a 12 month plot of fuel economy for the little Subaru.  The mileage isn't great for such a tiny car, but it's AWD, so that's the reason it's not that great.

What I've noticed is that the mileage is better during the summer months, then gets worse over winter.

Below is a plot for the entire time I've been using the app.  Just by glancing at the trend, you can tell whether it's winter or summer.

I'm left wondering whether it's a fuel blend change, whether the car runs a richer mixture during cold weather, due to winter tires, or a combination of all three!