On 'Pure' Gasoline, Your Mileage May Vary: What's The Difference?

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Non-ethanol gasoline pump

Non-ethanol gasoline pump

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Unless you're the type to very closely read the fine print on the face of fuel pumps, you might not know that the vast majority of U.S. gasoline is truly ten-percent home grown—that's ten-percent ethanol, and with that ethanol almost certainly from corn.

The upsides of adding more ethanol to fuel include a reduced reliance on foreign petroleum production and reduced emissions of some air pollutants. Ethanol also raises gasoline's octane rating without the greater use of some of ingredients that may be more harmful to the environment (or to people).

But the primary downside of adding more ethanol to fuel—aside from issues relating to corn crops and food supply—is that it lowers the actual energy content of gasoline. According to the U.S. EPA, vehicles will typically get three to four percent fewer miles per gallon on E10 than on what it terms 'straight gasoline.' And of course, those are extra gallons of ethanol that you'll need to truck around the country.

Lower mileage...but how much lower?

The three-to-four-percent figure is what's widely accepted by the industry; on the other hand, the American Coalition for Ethanol found, through their own study, found that E10 only lowers mpg by about 1.5 percent on average.

On older vehicles, the affects of ethanol are a little more pronounced. Especially in vehicles from the 1980s and earlier, rubber-containing components such as gaskets, seals, and fuel lines can harden and fail earlier when run on ethanol-containing fuel, according to restorers, mechanics, and classic-car enthusiasts. Vehicles built in 2001 or later have already been approved for 15-percent ethanol, though.

Non-ethanol gasoline pump

Non-ethanol gasoline pump

Enlarge Photo
And the proliferation of E10 in just about every neighborhood, suburb, and truck-stop gas pump has led some classic-car owners—along with some other enthusiasts seeking better mileage or better performance—to go out of their ways for 'pure gasoline.'

In all fairness, that's not the right term. All gasoline is a blend of ingredients and compounds—like toluene, xylene, pentane, butane, heptane, napthalene, isopentane, and others—and ethanol can be one of them.

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Comments (15)
  1. It seems rather odd that adding 10% ethanol should reduce mileage by about that same 10%. It would appear the ethanol has no energy value whatsoever then. Unless there is a huge scam going on and water is added rather than ethanol the 10% number is unlikely.

  2. this article explains why ethanol costs so much mileage http://www.stgeorgeutah.com/news/archive/2012/05/04/op-ed-counterpoint-to-analysis-gas-mileage-going-down/

  3. Thanks for the link.

    The explanation offered in this story sounds rather hairy and I think a reduction in mileage equal to the amount of ethanol added would have drawn more attention than it did, but that's for the experts to decide.

    At least this sentence offers logic that can't be denied:

    "We know we don’t experience mileage losses if we don’t add ethanol to gasoline in the first place, which is something even ethanol’s supporters don’t argue against".

    ....guess they wouldn't, LOL!

  4. there is NO DOUBT whatsoever in my mind that your 10% increase in gas mileage was not all due to change in gasoline. have had this discussion a MILLION times already and i also did this test in my Prius several years ago when one could get pure gas easily (Have not been able to do that in my area for decades) in OR. and it got me no more than 1-2 mpg making it at most 4% or so. if you work the math you will find ethanol to have about 66% (76,100 verses 114,100 BTU/gal) the energy of gasoline. so 10% ethanol will have 110,300 BTUS or 96.67% of the energy of whole gasoline

  5. so ethanol is a wash, a complete waste of time,, I've heard the reason the price of oil is so high is twofold, one is using corn to produce a fuel that has no benefit lowers the value of the dollar,, so we need more dollars to buy a barrel of oil,, the other is that ethanol costs more than gasoline to produce,, so the government turns a blind eye to speculators driving up oil prices to the point ethanol can compete with gasoline,, the reasons are political having to do with who controls the vote of farmers in the Midwest

  6. In my experience, 10% Ethanol will reduce a 30mpg car by about 1-2mpg comparing with Chevron's 100% gasoline at 87 grade.

    But in general, the cheap Costco gas of 90% gas cost at least $0.10 less per gallon than the Chevron 100% gas. So, it is still a little bit ahead in the Pure Gas mode.

    I haven't been able to see the difference in my Volt at premium gas between the two. However, Chevron gas stations dispense the Premium with their own nozzle and Costco gas station use a "mixed" single nozzle with their gas. I could be getting even less than Premium gas...

  7. Why is official data for vehcles using ethanel-blended fuels so hard to find? The wide spread use of ethanel-blended gasoline at times seems like a mismanaged science experiment.

    I assume EPA milage data is based on test with 'pure' gasoline. It would good to know if milage varies by more that 3-4%. What variation is expected between using E10 vs. E15? Does ethanel-blended fuel effect milage under some driving conditions more/less than other driving conditions?

  8. The EPA test uses pure gasoline that is blended specifically for the test so it is very consistent. You can find mileage figures for cars running on 85% ethanol on the EPA web site (www.fueleconomy.gov) to see the mileage deterioration (e.g., Ford Focus gas 27/38/31; E85 20/28/23).

    For blends in the middle, you can interpolate using the 66% energy level of ethanol cited earlier. E10 would result in approx. 3% loss; E15 approx. 5% loss.

    Otherwise, you won't find a lot of hard data. What you will find is interest groups posting their own "findings" including some in corn states arguing that one can get better mileage with ethanol than gas in turbo applications.

  9. Going from E10 Regular to E0 Premium in a Volt gives its CS-mode about a 12% increase in mileage (mpg) from about 37 to 42+mpg. Though some people do use Regular in Volts, they should use Premium. Many cars could get better mpg with Premium over E10 Regular 87 octane as well but most people don't want to pay the extra cents/gallon. Heck - most people won't keep their tires properly inflated and they'll get 3-5% better mpg if they did that.

  10. I have experienced a 10% loss in mpg on 2 different vehicles, a 2001 Acura MDX and a 2004 Ford F150. While I have no doubt that vehicles tuned specifically for E10 may exhibit only a small drop in mpg, that doesn't help me on older vehicles. As others have said it does not benefit the US economy to have 10% of your gasoline replaced with Ethanol to experience a 10% drop in fuel economy. We are actually worse off.

  11. I also disagree with the statement in the article that E15 is just around the corner - it is not. While you might be able to find E15 at a few pumps nationwide, it will not be readily available for a long time, if ever. The reason is simple, unless the EPA or another Government entity will grant the refiners immunity for damage caused by E15, then they will not sell it.

  12. I think the most important item the article briefly touches on is the fact that ethanol is made here in the US and sold here in the US. This in turn keeps a little more of the money spent on gasoline here in the US rather than sending it all to oil importers. I think the idea of having more of the oil money stay here in the US rather than send it all overseas is a valid enough reason to blend ethanol with gas and sell it here regardless of it's lower mpg. Ethanol production has generated a whole sub-industry in the US and none of the cost benefit numbers seem to reflect that. Anyone ever do a survey of how many folks in the US are employed in the ethanol business and the amounts of $$$ they earn?

  13. I have many years(to eliminate weather, seasonal & filling differences) comparing mpg between 100% gasoline(ethanol-free) & 10% ethanol blends in 3 cars. All cars show mpg increases of 8%, 7% & 5% for 100% gasoline. All engines are smoother, quieter, & have extra low rpm torque, such that less shifting is necessary to climb hills.

    My present 2013 Elantra, bad mouthed for poor mpg, obtained 43mpg with its first tank of 100% gasoline, the last 4 of 5 tanks got 40mpg or more, & now is averaging 39+mpg with 15% city driving. The engine is so smooth, Elantra holds 6th gear to as slow as 35mph.

  14. Update & expanding: Now, 5 of 6 tanks got 40mpg or more. Along with the 15% city driving, all tanks were emptied over 4 to 7 plus days with warm up & cooling periods, & weren't highway trips where tanks were used up within hours & no cooling periods.

  15. Wow! An auto outfit, & you aren't hailing the ability of the gasoline engine Veloster, designed & built to burn 100% gasoline, to gain 3mpg over the misery & powerlessness of 10% ethanol blends that give almost 9% less mpg! & then, you accept the mpg rating for 10% ethanol blends, by an ethanol propaganda puff. This is not rocket science. Using just 10% ethanol in gasoline lowers mpg by almost 9%, means that the ethanol is providing almost no power in the gasoline engine.

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