Does EPA test with Ethanol Gas for MPG

The test methods and rules are published and available online.

When I last looked, pre-2008, they had accumulated some adjustment rules to account for fuel blends of differing energy content, i.e. ethanol and other oxygenates. All results were adjusted back to reflect a traditional non-oxygenated fuel.

Though memory is hazy, I don't think they even measure fuel volume at all, but instead measure the various forms of carbon coming out of the tailpipe.

The change in MPG labels from the 2008 rule is greater than the small loss from using ethanol fuel.

 

10% ethanol will not result in a 10% loss in fuel efficiency, unless the BTU output of ethanol is zero, it isn't

 

FWIW

Ethanol and Fuel Mileage | American Fuels

 

+1

 

I don't think anyone here disputes the fact that ethanol contains less specific energy than gasoline. We do dispute the 10% reduction figure for 10% ethanol, as that is incorrect by inspection.

It is easier to notice mileage variations with the Prius. The Prius mileage is so good that the absolute numbers are much larger than that for low mileage cars. The actual percentage change may be a bit larger, but it is in the same neighborhood.

Tom

 

The "studies" (particularly by those pushing ethanol) are questionable considering the loss in energy content. Rather than seeing a reduction in overall mpg loss, my calcs of driving my truck with/without E10 was a much higher loss than the energy content reduction.

Here is a recent article from Down Under showing a 4.2% loss in a Camry. Porsche says their Euro testing is resulting in a 3% loss. False economy: E10 fuel isn't cheaper or greener - National - BrisbaneTimes

This is inline withe the US govt's. own studies that indicate ~4% reduction in fuel economy with E10. http://www1.eere.energy.gov/vehiclesandfuels/pdfs/program/int_blends_rpt_1.pdf

It is unfortunate that we are stuck buying this E10 against our will in many jurisdictions. Not only is it less economical, despite subsidies, but the fossil fuel use to make the ethanol likely makes this a heavily negative use of resources.

Where you can, try driving with both on back-to-back tanks. Then draw your own conclusions.

 

Three or four percent is believable, ten percent isn't.

 

It's clearly not 10% for those that use only E10. My average certainly supports that. There could be a blending effect at play, unless those complaining are literally running their tank drive before filling up. Studies have shown results vary based on the level of ethanol, having less of an impact in some cases.
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Ten percent is possible, although unlikely. I wouldn't consider it to be the norm any more than I would "1.4%" which immediately sets off the BS detectors. If the greater part of the actual power lost is *needed* to overcome overhead in the motive system, then it could very well be magnified.

It could be analogous to skimming 3-4% of the revenue of a product...the impact on profitability of that product is more than a unitary multiple of skim. In the highway trips where I've compared mpg in the truck I would put the factor at something like 1.5 - 2X. Stop and go acceleration could have similar factors. Of course this will vary depending on vehicle and driving conditions.

There is also some small effect from water dilution. Assuming the resultant mixture is not saturated with water the impact should be small and the extra vaporization energy not too great compared to the heating value. (Although it takes about 6-7 times as much energy to boil a pound of water as a pound of gasoline, the heating content of the fuel is much higher.)