Why does colder air hurt mpg?

nismotigerwvu

Golden Member
May 13, 2004
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Exactly, denser air mean more oxygen. More oxygen means you need more fuel to keep your air to fuel ratio the same as it was at the higher temp. At least you are making more horsepower :)
 

mooseracing

Golden Member
Mar 9, 2006
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Think of it in carb terms, when it's colder you have to use more choke. Therefore more gas. Simple.
 

overst33r

Diamond Member
Oct 3, 2004
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In addition to the above, air resistance is increased due to the density change.
 

herm0016

Diamond Member
Feb 26, 2005
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but you do create more horsepower too. so its not much difference in the long run. also, your engine will run less efficiently until it warms up to the proper temp.
 

marvdmartian

Diamond Member
Apr 12, 2002
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Let's not forget the wussies that take time to warm their cars up in the wintertime, then wonder why their mileage takes a 2-3mpg hit. ;)
 

potato28

Diamond Member
Jun 27, 2005
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Originally posted by: marvdmartian
Let's not forget the wussies that take time to warm their cars up in the wintertime, then wonder why their mileage takes a 2-3mpg hit. ;)

Well you do need to warm it up, but some people around here warm them up for 5 minutes in -10C weather. Now that's just crazy.
 

thomsbrain

Lifer
Dec 4, 2001
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I don't see any logical connection between colder air and lower MPG. Yes, your engine uses "more" gas to compensate for the denser air, but since your gas is likely to be cold, too, it is ALSO denser. Cold gas increases mileage. I'd be surprised if the computer actually calls for more gallons per mile, with all else being equal.

I think what people are noticing has a lot more to do with winter blend fuels with lower-energy-density additives and longer warm-up times. Cold engines KILL mileage.
 

Zenmervolt

Elite member
Oct 22, 2000
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Originally posted by: thomsbrain
I don't see any logical connection between colder air and lower MPG. Yes, your engine uses "more" gas to compensate for the denser air, but since your gas is likely to be cold, too, it is ALSO denser. Cold gas increases mileage. I'd be surprised if the computer actually calls for more gallons per mile, with all else being equal.

I think what people are noticing has a lot more to do with winter blend fuels with lower-energy-density additives and longer warm-up times. Cold engines KILL mileage.

Air density changes faster than fuel density.

ZV
 

Ronstang

Lifer
Jul 8, 2000
12,493
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Originally posted by: Zenmervolt
Originally posted by: thomsbrain
I don't see any logical connection between colder air and lower MPG. Yes, your engine uses "more" gas to compensate for the denser air, but since your gas is likely to be cold, too, it is ALSO denser. Cold gas increases mileage. I'd be surprised if the computer actually calls for more gallons per mile, with all else being equal.

I think what people are noticing has a lot more to do with winter blend fuels with lower-energy-density additives and longer warm-up times. Cold engines KILL mileage.

Air density changes faster than fuel density.

ZV

But you need less air to make the same HP to keep the car going and thus less gas too. If your mileage drops in colder temps it is because you are driving more spirited because the car is a little more peppy.

The only reason you see a drop in fuel economy these days during the winter months is because our stupid government thinks it has the knowledge to choose how to blend gasoline.
 

Zenmervolt

Elite member
Oct 22, 2000
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Originally posted by: Ronstang
Originally posted by: Zenmervolt
Originally posted by: thomsbrain
I don't see any logical connection between colder air and lower MPG. Yes, your engine uses "more" gas to compensate for the denser air, but since your gas is likely to be cold, too, it is ALSO denser. Cold gas increases mileage. I'd be surprised if the computer actually calls for more gallons per mile, with all else being equal.

I think what people are noticing has a lot more to do with winter blend fuels with lower-energy-density additives and longer warm-up times. Cold engines KILL mileage.

Air density changes faster than fuel density.

ZV

But you need less air to make the same HP to keep the car going and thus less gas too. If your mileage drops in colder temps it is because you are driving more spirited because the car is a little more peppy.

The only reason you see a drop in fuel economy these days during the winter months is because our stupid government thinks it has the knowledge to choose how to blend gasoline.

Well, technically, since you're using a slightly smaller throttle opening to produce the same amount of power (due to needing a lower volume of air) the engine's pumping losses increase slightly, reducing efficiency. But that's a very, very small affect and I think that in the practical world you're right. :)

ZV
 

Elstupido

Senior member
Jan 28, 2008
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I have found that winter blend gasoline is for the most part, responsible doe the drop in mileage, not to mention 0 mpg when warming up the engine, which is essential in below 0 degrees f temps.
 

getbush

Golden Member
Jan 19, 2001
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Between winter fuel, warming up , pushing snow, and snow tires, I don't even bother to check mileage in the winter.
 

RU482

Lifer
Apr 9, 2000
12,689
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Originally posted by: Elstupido
I have found that winter blend gasoline is for the most part, responsible doe the drop in mileage, not to mention 0 mpg when warming up the engine, which is essential in below 0 degrees f temps.

Does the entire country get winter blends? I thought it was just mountain states, California, and the east coast cities.

Here in the midwest, the mileage my impala gets tanks from about 28MPG in the summer to about 24MPG in the winter (even during the "winter" weeks when it's in the 60's and 70's).
Same thing with the Bonneville before it, and the accord before it, and the lesabre before it.