[Rum]

As part of my demise into the doldrums of fuel economy, I have been reading various articles online. I notice folks say warmer climate contributes to better gas mileage.

Okay I understand if your metal parts and fluids are damn near frozen, or at least very cold, that the friction is higher, thus bad MPG. I get that.

But why, for example, do people claim better MPG when it's 95 degrees out versus 75 degrees out? I mean, that whole friction argument doesn't seem to be relevant in this temperature range. Furthermore, the chemistry corner of my brain remembers the Ideal Gas Law, suggesting colder air is denser and thus has more oxygen in it for the combustion process. So, shouldn't cooler air contribute to better MPG? After all, isn't that why CAI companies boast not only extra power, but extra fuel economy?

Please elighten. Thank you.

[ToeKutter]

I'm thinking the colder air (which is denser) would automatically include more gasoline in the mixture, therefore you'd use more gasoline when cold. The more air you put into the engine, the more fuel goes with it (given the same A/F ratio curve in the cold vs. warm conditions).
Just off the top of my head. Interested to hear more on the subject.....

[Rum]

^^^This is true of course but then wouldn't the driver naturally compensate by pushing less pedal?

[chaos311clarity]

the gas quality also changes seasonally.

[ake109]

Its a not a one way straight line thingy.

I distinctly remember reading a factory manual (Nissan or Skoda IIRC) where it showed a Fuel Consumption vs Ambient Temp graph and the Fuel Consumption was lowest at about 20 deg Celcius and goes down when its either hotter or colder.

[torquemada]

I don´t believe it.
If your theory is true, we all can get rid of our TMICs and FMICs

I call it nonsense. The colder the better. It´s only the startup what kills the better mpg in cold weather.

[BlueSubaru]

I read somwhere that those hypermiler guys are working on a hai (hot air intake) to get even better gas milage, it might get better gas milage but hot air=low power.

[ToeKutter]

Haha...hot air intake! I love it! just yank the radiator out of your car and you'll be running hot (and saving gas!!) in no time! Then when the engine blows, you'll save a fortune on gas....

[rj45]

Cold air is dense and more difficult to drive through than warmer, less dense air. More drag equals less fuel efficiency.

[07Ltd#767]

Originally Posted by ake109

Its a not a one way straight line thingy.

I distinctly remember reading a factory manual (Nissan or Skoda IIRC) where it showed a Fuel Consumption vs Ambient Temp graph and the Fuel Consumption was lowest at about 20 deg Celcius and goes down when its either hotter or colder.

Though the exact number isn't correct, the theory is there. I remember a few years ago when I took IC (Internal combustion) Engines at Tech they were talking about the perfect ratio of density vs. temperature. Lower temps helped the increase in delta T, but the density allowed less air in. More air = more power. There is a happy medium where the two coexist, and anything on either side of the equilibrium chart will negatively effect power / performance / gas mileage.

Wow....

And I thought alcohol and other substances rid my brain of all its knowledgeable cells when I was in college...how did that stick around?

[UturnSTi]

Cold Air = Denser Air; Hot Air = Less Dense Air.

Cold Compressed Air = Greater Explosive Potential

Hot Compressed Air = Lower Explosive Potential than ^^

Less fuel is needed to create a burn with Cold Compressed Air than with Hot Compressed Air.

Maybe wrong but I believe this is correct... For the best MPG you'd want the coldest air possible going into the engine (I get better mpg in the winter months)

[07Ltd#767]

Originally Posted by UturnSTi

Maybe wrong but I believe this is correct... For the best MPG you'd want the coldest air possible going into the engine (I get better mpg in the winter months)

not quite...like you said, cold air = denser. you can get more air into the cylinder when it's warmer, thus potentially increasing your afr. However, too hot and you lose the explosive power, like you mentioned. Therefore, there is a happy equilibrium, it's just hard to pinpoint

[solovus]

They put additives in the gas when it is cold to prevent the fuel from freezing...this in trun reduces gas mileage.

[07Ltd#767]

Originally Posted by solovus

They put additives in the gas when it is cold to prevent the fuel from freezing...this in trun reduces gas mileage.

What is the freezing point of unleaded gasoline? - Q&A

[Arcticsun]

In this situations, it is best to look at the limits. Of course the limits are, no air, and air that is super dense. No air = no fuel = stand-still. Super dense = lots of fuel = lots of power (that you don't need when cruising on the freeway.)

All to do with density and AFR. AFR being more or less constant throughout. The hotter is is, the less dense the air. Ergo, less air you have, the less fuel you need.

But of course you get much less power because you aren't burning as much air and fuel.