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Old 09-13-2017, 07:40 AM   #1
mfifield01
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MPG at Altitude (Gas)

I just got back from a trip to Pagosa Springs (from Austin). I noticed that my MPG was considerably better at higher altitudes. From Santa Fe to Pagosa, I was seeing ~11 MPG. I manually calculated on the way back and got 10.6 (Pagosa to Santa Fe). I typically get about ~9 around Texas. This is an NA Gas Engine (5.7l Hemi). My only explanation would be gas without ethanol or less wind resistance. Any thoughts?
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Old 09-13-2017, 09:29 AM   #2
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We don't really have any high altitudes in the east so I haven't noticed. Switching to synthetic oil made a 2mpg increase for me.


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Old 09-13-2017, 09:46 AM   #3
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I have had the same experience, better mileage outside of TX, with my 5.0 V8 F150 and chalked it up to less ethanol.

I guess it could be elevation or both, not sure.

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Old 09-13-2017, 11:16 AM   #4
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With all the fancy computer controlled fuel injection now days you would think there would be no differences. There is some physics involved that may explain it somewhat. At altitude the air is cold and dense where as in good 'ol Texas its fairly humid and less dense......cold air is heavier than hot air, denser, so it contains more oxygen molecules per pound. Small aircraft have the means to manually adjust the air/fuel mixture at altitude because they are still pretty much old fashioned carbureted engines, otherwise they could run rich to the point that it would flood out and stop running, depending on altitude.
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Old 09-13-2017, 01:19 PM   #5
chuckster57
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MPG at Altitude (Gas)

Computer controlled engines have the ability to change fuel/air ratio on the fly. In simple terms, OBD II was mandated in 1996 and it is one computer controlling a number of different systems. I can't remember right now how many times a minute it would "adjust" things. C.A.N. was mandated in 2006 (if I remember right), and had a number of computers that communicated with a central computer. If my mind is still working, I believe it made adjustments 60X a second.

With all that in mind, a 1MPG difference may be explained away in any number of ways.
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Old 09-13-2017, 06:32 PM   #6
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Originally Posted by mfifield01 View Post
I just got back from a trip to Pagosa Springs (from Austin). I noticed that my MPG was considerably better at higher altitudes. From Santa Fe to Pagosa, I was seeing ~11 MPG. I manually calculated on the way back and got 10.6 (Pagosa to Santa Fe). I typically get about ~9 around Texas. This is an NA Gas Engine (5.7l Hemi). My only explanation would be gas without ethanol or less wind resistance. Any thoughts?
With a NA engine, you will experience significantly reduced power at altitude. Therefore, you will burn less fuel. How much less is debatable.
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Old 09-13-2017, 06:46 PM   #7
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I know growing up with my family in the early 90s we got a consistent 2 mpg better when towing at altitude. This phenomenon was observed on multiple trips over several years.
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Old 09-13-2017, 07:27 PM   #8
mtofell
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Switching to synthetic oil made a 2mpg increase for me.
Synthetic oil is typically good for a few % improvement at best. That's some magical oil you got a hold of.
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Old 09-13-2017, 09:46 PM   #9
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My only explanation would be gas without ethanol or less wind resistance. Any thoughts?
Ethanol burns leaner and requires more. Say yes that's why the increase in mileage. As mentioned about the on board computer. It's sensing a richer burn and is compensating for it.
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Old 09-14-2017, 07:35 AM   #10
mfifield01
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If ethanol is the factor, it reduces gas mileage by about 18% (maybe more).

Another thing that doesn't make sense, is engine load. My engine was working harder to climb to that altitude.
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