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Gas Mileage: Finally Converting from Ethanol-10 to Premium?

Last updated on 2011.08.18

Monday before last, I drove out to Spearfish and got a job. Last Monday, I drove out to Spearfish and got an apartment. This coming Sunday, I haul family, teacher shoes, and bicycles to Spearfish. Work starts this coming Monday.

Among the joys of five traversals of the great state of South Dakota in 14 days is the opportunity to test my 2002 VW Beetle's gas mileage. I've used 89-octane 10% ethanol blend pretty regularly since the 1990s, largely because my taxes already paid for some of it and because it's usually the cheapest juice at South Dakota pumps. Paying 20 or 30 cents more for 91-octane premium.

The following data from five tanks of gas in the trusty Bug have me wondering if maybe I ought to switch to premium. The columns tell you...

  1. where and when I bought the gas;
  2. what type of fuel (10% ethanol or no ethanol, then octane rating);
  3. price per gallon (rounded up!);
  4. miles per gallon;
  5. at that mpg, how many gallons would be needed to go 400 miles;
  6. at that pump price, how much that 400-mile trip would cost;
  7. what roads I took (matters, since I went 60-65 on SD-34, 70-75 on I-90).
station fuel/
$/gal mpg gal to go
400 miles
cost to go
400 miles
HumDinger2, Wessington Springs, 8/8 Ethanol-10/89 $3.68 28.46 14.05 $51.70 SD-34/I-90
Speedy, Spearfish, 8/8 no eth./91 $3.90 37.51 10.66 $41.58 SD-34
Fresh Start, Pierre, 8/8 E-10/89 $3.60 32.22 12.41 $44.67 SD-34
Jake's Corner, Winfred, 8/15 E-10/89 $3.42 31.28 12.79 $43.72 SD-34
Safeway, Spearfish, 8/15 no eth/91 $3.90 35.31 11.33 $44.16 I-90/SD-34

Now there are all sorts of factors to confound hard scientific conclusions, not the least of which is the fact that I never drained the tank completely before adding new fuel (unwise, especially on Highway 34 west of Pierre!).

But my first tank of 91-octane, zero-ethanol gas from the Spearfish Speedy station by Exit 14 produced a pretty clear mileage advantage, giving me 37.5 miles per gallon. The same product from Spearfish Safeway gave me 35.3 mpg. Not bad, considering that over 5500 mild-weather miles since May, the Bug has averaged 31.7 mpg.

The best mileage I've gotten on 89-octane, 10% ethanol blend came on a fill-up I bought from the Madison BP in May. I drove across Minnesota on Highway 14, stayed under 60, and coasted into every town. That got me 34.0 mpg.

Now the real metric that matters isn't how much I pay in one visit to the pump; it's how much it costs me to cover a certain distance. Compare Speedy's 91 with Jake's 89. Speedy's gas cost me a premium of 48 cents per gallon. But I burned so much less of it at 37.5 mpg that, on side-by-side 400-mile trips, the high-octane, no-ethanol fuel from Spearfish would have saved me $2.14.

Jake's gas still beat Safeway's for total 400-mile cost by 44 cents. But at the point where my savings won't buy a Hostess pie, I turn to other factors. Do I do the Earth a favor by burning less fuel? Does that extra 44 cents leave my engine cleaner than regular gas with a shot of corn whiskey?

I would enjoy hearing your experiences, dear motoring readers, with different blends and grades of gasoline and ethanol. I'll keep you posted on my mileage data, but be forewarned: living five blocks from the office and the grocery store is going to reduce my dataset significantly. And for once, I'll be thrilled to have less data.

Update 21:34 CDT: One thing I don't want to have to factor into my mileage calculations: baseball-sized hail near 1880s Town on I-90! Ouch!


  1. Jesse Johnson 2011.08.17

    I am also interested to see what others are getting for mileage as I am sure the results vary greatly between different manufacturers. But I would like to point out the advantages of ethanol. Ethanol is an entirely local and domestic product that is helping to reduce our countries dependence on foreign oil. Using ethanol reduces greenhouse gas emissions by 52% and replaces nasty toxins used in non-ethanol blends. Using ethanol also supports the thousands of American jobs created by the industry and our countries family farmers.

  2. Jana 2011.08.17

    I really want to think that buying ethanol is good. Not just for me but everyone else too. But sometimes I have my doubts. I want to believe it's good for our economy, want to believe it's good for the environment...but a little conflicted and keep wondering what's true and what's not.

    We've gotten the same kind of results and it drives me crazy. Guessing our real test will be when they pull the subsidy away and we make the choice on what's best for us as we fill the soccer mom van up on our next trip.

  3. Jenae Hansen 2011.08.18

    As a girl born and raised on a corn farm I just don't know why someone would not invest their fuel money in ethanol. I think it does do the earth some good and our local economies (vs forgein oil). I have done hundres of hours worth o research on this very topic! I also as a suggestion buy ethanol fuel at a Cenex or other coop station. They generally will use a higher quality of gasoline to mix with the ethanol.

  4. Stan Gibilisco 2011.08.18

    Three thoughts ...

    (1) I nornally use premium gas (91 octane or higher, no ethanol) from brand-name sources (Exxon, Shell, etc.) because I subscribe to the "popular wisdom" that it's best for the engine.

    (2) I use gas "spiked" with ethanol when, but only when, I have to drive in below-zero weather. Ethanol helps to prevent gas-line freeze, so they say.

    (3) Better park your car under cover out here in the summer. Hail can come out of nowhere in June, July, and August.

  5. Warren Phear 2011.08.18

    I would check with a certified mechanic before switching over. I tried the same thing with my two vehicles a couple of years ago. The "check engine" light came on both vehicles within a month. Has something to with the many different sensors and how they read differently on your vehicles computer module.

  6. Heather Lee 2011.08.18

    I have recently done the same switching from ethonal blend to premium. I have noticed a increase in milage but also have noticed in my 2002 minivan with high miles that the engine runs better. I have increased the milage from 18 or 19 to 24 or 25.

  7. larry kurtz 2011.08.18

    i looped Spearditch last night looking at all the real estate for sale: wow, what a mess! Sitting in the Pumphouse in Deadwood drinking coffee. Hope to see you next week?

  8. Michael Black 2011.08.18

    Ethanol is great as an additive to reduce smog in the big cities, but it does take more energy than we realize to bring the corn to the plant and process it.

    Ethanol has driven up the price of corn and other crops as more and more land is devoted to its production. Land and cash rent prices have skyrocketed eliminating young farmers chances at starting operations.

  9. Steve Sibson 2011.08.18

    The hail was caused by global warming.

  10. caheidelberger Post author | 2011.08.18

    Warren: Yikes! Anyone else have that happen? If premium is cleaner fuel, how could that mess up sensors? Bummer!

    Heather: that's a big difference! Keep me posted on whether the minivan keeps running right.

  11. moses 2011.08.18


    [CAH: Read that first line again, my friend: Spearfish. ;-)]

  12. RGoeman 2011.08.18

    Took the VW TDI diesel Jetta to Florida and back, averaged 45.5 mpg for the 3000 mile trip. Sorry, no ethanol formula for diesel yet, but if they come up with it, I'm there!

  13. Gary D 2011.08.18

    Michael: I find your statements on the amount of energy it takes to produce and process corn interesting. Where do you get your facts? The Oil companies?

    Do you think that it take no energy to produce, ship and process oil? What about the cost to the military to keep the oil shipping lanes open. Is that all free?

    We are producing more corn on less land using less rescources than we were 10 years ago, so how can this be?

    As far as the price of corn, there are many other factors that come into play besides ethanol.

    We have a growing world population that was short of feed for their livestock(China). Last year there was no wheat crop in the Ukraine a major producer of wheat so the market had to get feed from somewhere and that was the US.

    Another factor is the value of the dollar compared to other currencies. Right now it is low so our products, corn, soybeans,wheat are cheaper to buy. I can just about gurantee you that if the value of the dollar rises exports will fall because it will be more expensive for these countries to purchase our products.

    So, I think your statement takes a very simplitic and uninformed view as to what exactly is causing the prices we have todoy in agricuture. Ethanol plays a part in this but it is a whole lot more complicated than that!

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