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Thread: Fuel Mileage

  1. #1
    Jr. Mechanic AzDragonLord's Avatar
    Join Date
    Aug 2010
    Florence, AZ...AKA just this side of hell!

    Default Fuel Mileage

    I run E85 fuel about 99% of the time in my 2009 Sierra. I make a lot of trips between Phoenix and Los Angeles and my MPGs typically run between 15-16. I check my mileage each tankful using the calculator-method.

    I've tried a few things to see if I can get better mileage, like keeping my highway speed at 65 (vs 75) during one entire trip which kept the RPMs below 2000, but did not increase my mileage at all. I also installed cruise control which helps me, but did nothing for my MPGs. I did install a bed cover which gave me a whopping 1 MPG increase...not much but every bit counts. I'm not a lead-foot and I keep the (still factory) tires at the recommended 35 PSI.

    I was really shocked to see that keeping my speed limited to 65 did nothing to help with mileage! Could the AFM system be hindering the typical MPG saving techniques?

    ================================================== =======
    2009 GMC Sierra 1500 WT with ... DU-HA underseat storage ; BAKFLIP G2 bed cover ;
    Rostra Cruise Control

  2. #2


    I run E85 too, and mostly run local roads back and forth to work (10 miles each way). I get about 10-11 MPG, which improves about 1-2 MPG running gas given the type of driving I do.

    My guess is that the majority of gas savings will come at acceleration, not at sustaining highway speed. Someone else who knows more about it will probably come along and have more ideas.

  3. #3

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    15-16 mpg with E85 is pretty decent- it is like getting 20-21 mpg on pure gasoline.
    E85 has just 75% of the energy of pure gasoline
    16/.75= 21.3 mpg.
    Ethanol has just 70% of the energy content- by volume- of gasoline.(the 70% is from memory- if I'm wrong calculate it like this)
    .85 x .7=.595 +.15= .745 so E85 has ~75% of the energy of gasoline.

    16mpg/.75=21 mpg equivalent.

    You are getting good mpg.Whatever tricks you are using-they are working. 16 mpg on E85 is GOOD! Like getting 21 mpg on gas.
    1998 suburban-
    1/2 ton

    199500 miles

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