Your mileage should increase because of cooler, damper weather, in theory at least. By cooler, I mean temperatures between 50 and 40. Damp means just above the dew point. Why do you think the tuners go for cool air boxes ... denser air! If the extra power isn't over used, more efficient combustion occurs.

All in theory since winter gasoline mixtures monkey with the theories and people tend to "warm up" their cars with extended idle time or rading the engines to speed up the warming process, especially "up Nawth" where it gets really cold on a regular basis.

Just my 2 cents, and probably worth even less..

 

The engine runs richer till it gets warmed up. The incoming air is cooler, but so is the engine.

 

I forgot the air conditioner. I turned the Fit's off yesterday for the first time since I bought it May 2, 2015. It was a very long, very hot summer. Heat index in the 100-115 range, real temperatures in the low 90s to 100. Yesterday, cold rain and 55 degree high. Next week back to seasonal highs of 75-80. Windows down, sunroof opened.

 

Yep, winter is singing "Get ready, cause here I come."

 

Yesterday I filled up with 0 miles on the range showing and the gas light had come on earlier that day. I knew I had plenty of miles left so I ignored the gas light. I still only filled up 8.855 gallons and calculated MPG was just shy of 42 MPG.

 

Negative, Ghostrider.

Combustion itself is perfectly efficient. When you're trying to cram as much gas and air as possible into the cylinder to produce more power, cold air helps a lot because there are more molecules in every cubic inch of it. We've got these wonderful sensors that tell the PCM what the outside air and engine coolant temps are, and the system runs richer or leaner as needed. The car doesn't waste gas, that's the driver's job.

But when you're trying to get things done with less gasoline, warmer is better. When you actually want power, floor it and it'll run richer. But when you're not stomping on the gas, power that isn't actually required to move you forward is completely wasted no matter how efficient the combustion is.

Denser air has another mileage penalty- aerodynamics. You're pushing a pretty unaerodynamic shape through air that is now denser. It takes more power to push you through the air today than it did in August.

 

I did say "in theory" and I didn't say whose theory. Your explanation seems at least as reasonable as any other.

On the aerodynamics, they just don't work when the speeds are at street and secondary highways ---50 mph and under. That's why the park bench wings/spoilers on the rear deck are more than silly and only add weight

 

Say that after riding a bicycle while holding an umbrella.

This isn't about turning airflow into downforce so we can do 5 gee corners, it's about pushing an unaerodynamic shape through air- and now that things are cooler, air that's denser than it was a short while ago. Drag kills fuel efficiency, and the Fit isn't well shaped for cutting through the air.

 

I like that the range on our cars (mine at least) hardly goes up. I noticed it for the first time in a year of owning my car yesterday when I suddenly went from 214 to 235, then up to 265. Both of those jumps happened over the course of about 5 seconds, jumping in 5 mile intervals. Before that, I was under the assumption that once it went down, the range never went back up.

 

I was thinking we were discussing autos, not umbrellas on bikes. Will the 3rd generation Fit is not the most aerodynamic in its class or in the crop of 2015-16 autos. But in this real world, the Fit is more aerodynamic than the previous 2 generations. Nose down, Kamnback (sp), slicker underside. It's still a brick, but a smoother brick, turned on its side. Now I don't know their respective CDs, but take the Stingray Corvette. Vents, scoops, side skirts. Some of the scoops direct the air into the injection systems, others cool the brakes or the transmission. At certain speeds, cool is important.

Now I know I'm in over my head, thermodynamics ended my "career" in engineering.

 

Don't forget that running your tank so low that you start to overheat the fuel pump. It has happened before on the Fit... best not to push your luck.
-bix