Warm air = better mpg?

[bluedeuce]

I've had a Scanguage in the smart for a few months now, long enough to notice that for steady highway cruising, the mileage readout climbs about 10mpg as the intake temperature goes from around 85 degrees to 95. Anyone else notice something similar?

[jwight]

Should be the other way around:

Effect Conditions Average Fuel Economy Reduction Maximum Fuel Reduction
Temperature 20F vs 77F 5.3% 13%
The above results mean that air at 77 degrees reduces fuel economy by 5.3-13%. Air temperature can affect mileage because cold air is denser than hot air, and denser air means more oxygen for combustion per unit of air (and therefore more energy). So, all other things being equal, this means the fuel mileage can be decreased during the summer compared to the winter.

http://www.bellperformance.net/pdf/F...ageFactors.pdf

[headless]

I agree with JWight, and there should also be a performance increase as the colder denser air means more horsepower.

[smrt4her]

We don't have a scanguage, but have noticed similar results. During the winter we averaged 35 mpg/city. As it has warmed up here, the same trips are averaging 41-42.

[ciscocali]

Gas expands when it is hot. That is why it is always better to fill your tank in the morning when the gas is cold. By the time the day gets hotter, your gas will expand, giving you better mileage for that tank.

I haven't personally tried it but in theory it sounds like it would work.

[The GMan]

I get the same performance difference on my motorcycle. In the winter, I get about 40 MPG on the highway, in summer its 45.
Probably due to two factors.
In the summer, air is less dense, so it requires less power to drive through the thinner air. Also, the less dense air results in less power available from the engine, meaning more MPG.
In the winter it is the opposite. The air is more dense, so it requires more power to push through it and you can get more power from the engine, so it reduces the MPGs.
It can also be sneaky. In the winter, with denser cold air, you feel the increased power of the engine, so you are tempted to goose the engine and floor it more often to experience the extra power available to you, further reducing your mileage.

[jwight]

Don't forget the other winter effects - more drivetrain friction loss as it takes longer for the fluids to reach operating temp, and many folks let their cars idle to warm up (not good) which kills mileage figures.

[Macaw]

Maybe I'm just old but cold used to mean running a richer mixture = more gas used and warmer was leaner mixture = less gas used....

[smart fortimo]

I'm getting a couple to several MPG's better now driving in the 40-60*F temps over the winter 5-35*F temps. Same route, same speeds, same, same, same everything.

[mvaldes]

Originally Posted by smart fortimo

I'm getting a couple to several MPG's better now driving in the 40-60*F temps over the winter 5-35*F temps. Same route, same speeds, same, same, same everything.

Same here