Any mpg difference between useing regular gas vs ethonol free gas?

Discussion in 'Clarity' started by glockgirl, Jan 13, 2019.

  1. glockgirl

    glockgirl Member

    When I have 100 + mi day, I end up driving on gas for a while. My car computer is telling me I'm getting 50-55mpg. I get ethonol free gas every chance I get. I was doing that a few yeas ago with my Prius and I did see about 4mpg different. It was worth it and easy to calculate. Anybody else seeing those # on trip calculator? Anybody else using the better gas?
  2. Sandroad

    Sandroad Well-Known Member

    Ethanol has less energy in a gallon than gasoline, so mpg is higher with ethanol free gas. How much higher depends on percent ethanol in the comparison fuel and how much ethanol is remaining in your tank from previous ethanol/gas fill ups.
    insightman likes this.
  3. MNSteve

    MNSteve Well-Known Member Subscriber

    "Ethanol contains about one-third less energy than gasoline. So, vehicles will typically go 3% to 4% fewer miles per gallon on E10 and 4% to 5% fewer on E15 than on 100% gasoline." [Oddly there is a reference to footnote 3, but no footnotes on the page.]

    This will no-doubt restart the religious war that has occured on other threads here, but my conclusion would be that if the E10 price was more than 3-4% less than the non-ethanol price (and it almost certainly will be, at least around here in corn country) I'd go with the E10.
  4. Clarity_Newbie

    Clarity_Newbie Active Member


    I am currently running non-ethanol, 89 octane strictly in HV mode for mpg calculations to respond to another thread.

    I will respond to this thread with results as well...probably at weeks end.
    glockgirl likes this.
  5. Clarity_Newbie

    Clarity_Newbie Active Member


    Over the last week, I ran in HV mode exclusively for 356 miles to try and gauge winter mpg. I ran 4 days just as I would normally do...nothing out of the ordinary. I conducted the test in normal HV mode only. I never used ECON or sport mode.
    I tend to run on 80% 2-lane and 4-lane roads with posted speeds limit 25 to 55 mph and 20% Interstate with posted speed limit 55 to 70 mph

    At the end I filled up with 6.80 gallons after 303* miles = 44.55 mpg in HV mode. *after 53 miles deduction for EV*

    Bottom line is 51.3 mpg in HV mode during the late summer on the first tank of non-ethanol gas as reported earlier.

    This go-a-round the Clarity managed 44.55 mpg under mild winter conditions on non-ethanol gas. My guts says there is a improvement in mpg. The book says may get gains in the 3% to 5% range...and I would say the Clarity got that at a minimum. The Prius gain of 4 mpg is a reasonable expectation for the Clarity as well...IMHO.

    As for cost/benefit...not really. $$$wise I would come out ahead using E10. I will conduct some more trials next summer if I get bored...will keep you posted if I do.

    I will continue to use non-ethanol however for multiple reasons. Pure gas or E10...whatever floats your canoe. No harm no foul.

    Hope this helps.

    Good luck.
    glockgirl, Remarksman and insightman like this.
  6. Fast Eddie B

    Fast Eddie B Active Member

    We’re lucky to have ethanol-free gas within just a few miles of both of our homes in N GA and E TN.

    I pay the price difference for a ROTAX-powered Light Sport plane and all my yard tools and generators where gas may sit for a while.

    Modern cars are all designed to tolerate ethanol well, and the small increase in mileage doesn’t justify the rather large increase in price. At least around here, and at least for me.
  7. weave

    weave Active Member Subscriber

    Around here ethanol-free is 20 cents a gallon more over the same grade of E10, which is like 10% premium these days. Even so, if I know that gas is going to be sitting in the tank for months, I'll pay it. Like I use it in my motorcycle during winter months.
  8. JustAnotherPoorDriver

    JustAnotherPoorDriver Active Member

    Yay, another pilot. If I still had a Cessna, It'd be a low compression one eligible for the MoGas STC. Unfortunately no plane right now, and no easy source for lead-free MoGas
  9. Fast Eddie B

    Fast Eddie B Active Member

    As promised, here are the prices at the Valero station near my N GA home...


    Prices for regular unleaded with ethanol are at least 10¢ or 20¢ cheaper across the line in TN. My plane needs 91+ octane, and prefers ethanol-free, so this works perfectly. Even at $3.139 it’s still cheaper than 100LL AVGAS and better for the ROTAX engine.

    We’ll be back in TN soon and I’ll post those prices as well.
  10. MNSteve

    MNSteve Well-Known Member Subscriber

    I'm missing something here. Your mileage improved from 51 to 45?
  11. Clarity_Newbie

    Clarity_Newbie Active Member


    Nothing mentioned about improved. Summer weather produced 51 mpg...Winter weather produced 44.

    The one critical factor that is different...the 51 mpg was figured on 100% around town with little interstate miles. (read average mph lower)

    The 44 mpg included a 80 mile interstate jaunt with corresponding speeds of up to 70 mph. (read average mph higher)

    It is commonly believed that vehicle mpg efficiency is tied directly to average mph and somewhat to big swings in ambient temperatures...(not to mention terrain and personal driving habits of course).

    Summer temps + local driving = higher mpg. Winter temps + local AND significant interstate driving = lower mpg.

    Obvious example why multiple tests need to be run using same standards under similar conditions. Only way to compare apples to apples instead of apples to pears. Go figure.

    If info on the parameters for the test this past week can be found at:

    Hope this helps.
    glockgirl likes this.
  12. MNSteve

    MNSteve Well-Known Member Subscriber

    I was trying to relate it to the thread topic, ethanol. Threads drift. I see your point now. Thanks.
  13. Fast Eddie B

    Fast Eddie B Active Member

    Our TN prices:


    Actually, 10¢ less for us with our Weigel’s card!

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