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Kajun Kim
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Discussion Starter · #1 ·
My Father in law is here visiting and he drives an 07 loaded Silverado. He says that he gets the best mileage early in the morning while it is cool. Has anyone looked at the difference that they get with their mileage in the cool weather versus what they get in the warmer temps?

My FIL says he gets about 24 or so with his truck (non modded) in the cooler temps and only gets about 18 or so in the hotter temps. Oh yeah he watches his on board computer like a hawk! hmmmm... just wondering if anyone has a resource that has given similar info.
 

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It is possible that the engine runs better in cooler conditions than in warmer conditions, but I don't see how that could effect the gas mileage, but now that you brought that to my attention it got me curious.:)
 

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Cooler air is more dense. In higher altitudes where the air is thinner, (or very hot days), you will use more fuel to compensate for the lack of oxygen.
 

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Cooler air is more dense. In higher altitudes where the air is thinner, (or very hot days), you will use more fuel to compensate for the lack of oxygen.
It is not an oxygen issue but the temperature and density of the fuel air charge.
 

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With all due respect to your FIL, there's absolutely, positively no way in h*ll he's getting a 6 mpg difference between morning drives and evening drives. We would all see that and we don't. As well, the DIC (Driver Information Center) on my 2005 Silverado is overly optimistic by 15-20% about my mpg's as compared to my actual simple calculation of miles driven/gallons used.

Some engines run a little better in cooler weather but not that much. That means in winter we'd all be getting something like 30% better mpg. (24 mpg vs 18mpg is a difference of 30%!). Does that mean, the colder the better? Would those driving H2 Hummers in Alaska during the winter get 40 mpg?

You ought to ask him to actually calculate his MPG to see how far his Silverado's mpg readout is off.

Sorry, but BALONEY!

DEWFPO
 

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Maybe he has the A/C off in the mornings, and on in the evenings.

Nah, too simple. :shrug03:
 

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There is a small difference in efficiency when the air is cooler. Part of it is the more dense air as mentioned in earlier posts. Another factor is an internal combustion engine is basically a heat engine; the bigger the difference in temperature between the hot gases in the combustion chamber and the cool air outside, the more efficient the engine. If you take this to the extreme (see the reference to AK above), other factors like thicker oil begin to overtake the effect of cooler air.

Considering all this, there would not be a 6 MPG difference.
 

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Kajun Kim
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Discussion Starter · #9 ·
Dew, my FIL is a guy that I listen to with respect BUT I don't really believe anything he says. That is why I asked you folks. I am a really sweet gal, trust me, I am, TOUGH as nails, but sweet. I just could not believe that he was getting that big of a difference when he drove in the early morning versus later in the day.


With all due respect to your FIL, there's absolutely, positively no way in h*ll he's getting a 6 mpg difference between morning drives and evening drives. We would all see that and we don't. As well, the DIC (Driver Information Center) on my 2005 Silverado is overly optimistic by 15-20% about my mpg's as compared to my actual simple calculation of miles driven/gallons used.

Some engines run a little better in cooler weather but not that much. That means in winter we'd all be getting something like 30% better mpg. (24 mpg vs 18mpg is a difference of 30%!). Does that mean, the colder the better? Would those driving H2 Hummers in Alaska during the winter get 40 mpg?

You ought to ask him to actually calculate his MPG to see how far his Silverado's mpg readout is off.

Sorry, but BALONEY!

DEWFPO
 

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It is not an oxygen issue but the temperature and density of the fuel air charge.
Higher density, more oxygen, lower density, less oxygen, would the terms not be interchangeable in reference to atmospheric conditions? Just curious as I thought the lower oxygen levels at lower density conditions meant more fuel was required to obtain the same or close too ignition levels.
 

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Higher density, more oxygen, lower density, less oxygen, would the terms not be interchangeable in reference to atmospheric conditions? Just curious as I thought the lower oxygen levels at lower density conditions meant more fuel was required to obtain the same or close too ignition levels.
Not quite. To maintain the same fuel air mixture (rich/lean) the engine computer will, for a certain throttle setting, actually use less fuel with less air density, not more. So it is the mass of the fuel-air charge to the cylinder which determines the power of the stroke.

So it is not a matter of the engine using more fuel in a condition of lower oxygen. It is a matter of the mass of the charge. Its fuel/oxygen ratio will be more or less the same (notwithstanding changes due to timing and so forth). So with less dense air, and consequently lower air mass flow, the engine computer will lean out the fuel charge, not increase it, so the fuel/air mixture (richness) stays the same.

That said, given the lower efficiency of the engine with higher air temperature, in order to obtain the same power, application of more throttle is required. But this increases both the air mass flow AND the amount of fuel provided by the injectors, keeping the same fuel mixture (more or less).

So it is not a tradeoff between oxygen and fuel. The ratio of those the same, (notwithstanding timing and other emission control subleties).
 

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Thank you! Very good explanation. :)

Not quite. To maintain the same fuel air mixture (rich/lean) the engine computer will, for a certain throttle setting, actually use less fuel with less air density, not more. So it is the mass of the fuel-air charge to the cylinder which determines the power of the stroke.

So it is not a matter of the engine using more fuel in a condition of lower oxygen. It is a matter of the mass of the charge. Its fuel/oxygen ratio will be more or less the same (notwithstanding changes due to timing and so forth). So with less dense air, and consequently lower air mass flow, the engine computer will lean out the fuel charge, not increase it, so the fuel/air mixture (richness) stays the same.

That said, given the lower efficiency of the engine with higher air temperature, in order to obtain the same power, application of more throttle is required. But this increases both the air mass flow AND the amount of fuel provided by the injectors, keeping the same fuel mixture (more or less).

So it is not a tradeoff between oxygen and fuel. The ratio of those the same, (notwithstanding timing and other emission control subleties).
 

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Kajun Kim
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Discussion Starter · #14 ·
Go to my photo gallery. There are a couple of them in there!
 

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Maybe he drives slower in the morning. Or, maybe there is less traffic so he can maintain a more constant speed with less waiting and stop & go. Too many variables in 'morning' vs. later in the day.
 

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Not quite. To maintain the same fuel air mixture (rich/lean) the engine computer will, for a certain throttle setting, actually use less fuel with less air density, not more. So it is the mass of the fuel-air charge to the cylinder which determines the power of the stroke.

So it is not a matter of the engine using more fuel in a condition of lower oxygen. It is a matter of the mass of the charge. Its fuel/oxygen ratio will be more or less the same (notwithstanding changes due to timing and so forth). So with less dense air, and consequently lower air mass flow, the engine computer will lean out the fuel charge, not increase it, so the fuel/air mixture (richness) stays the same.

That said, given the lower efficiency of the engine with higher air temperature, in order to obtain the same power, application of more throttle is required. But this increases both the air mass flow AND the amount of fuel provided by the injectors, keeping the same fuel mixture (more or less).

So it is not a tradeoff between oxygen and fuel. The ratio of those the same, (notwithstanding timing and other emission control subleties).
Well done White Rim. DEWFPO
 

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Dew, my FIL is a guy that I listen to with respect BUT I don't really believe anything he says. That is why I asked you folks. I am a really sweet gal, trust me, I am, TOUGH as nails, but sweet. I just could not believe that he was getting that big of a difference when he drove in the early morning versus later in the day.
Hi Kim, I know what you mean. I married a southern gal myself. Sweet as pie but tough as nails. I wouldn't have it any other way.:rocker:

DEWFPO
 

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might be something to this here in hawaii it is always hot and i am stock and the best mileage i have ever gotten is 16 MPG
 

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Kajun Kim
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Discussion Starter · #20 ·
Hi Kim, I know what you mean. I married a southern gal myself. Sweet as pie but tough as nails. I wouldn't have it any other way.:rocker:

DEWFPO
That's what I am talking about!!!!!:clap: BTW, the FIL does not really "get" me. He tells the hubby all the time that he would not put up with me. Boy oh Boy. I used to enjoy the occasional throw down......:rofl::rofl:
 
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