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Does Ethanol Really Reduce Your Gas Mileage?

I've always been interested in getting the most out of my vehicles from a fuel efficiency standpoint.

The advertisement from a local chain of filling stations for ethanol treated gasoline, also known as E10.

The advertisement from a local chain of filling stations for ethanol treated gasoline, also known as E10.

America's Fuel

A local gas station chain markets their regular unleaded gasoline as "ethanol enhanced." The use of the word “enhanced” is curious: it implies that there is some benefit or advantage to choosing this gasoline over other available products. Messages on the pump further add that this is “America’s Fuel” and that it may contain up to 10% ethanol. This ethanol-modified product is commonly called E10.

As an alternative, the chain also offers an ethanol-free 87 octane product called PureMax, which is an interesting name in its own right. Another gas station just down the street calls their ethanol-free fuel "Pure Gas" and proudly advertises that it will improve your gas mileage by 25% over ethanol grades. Pure gas is typically more expensive than E10 with the same octane rating. For example, during my last visit, the E10 cost $3.299 per gallon while the PureMax was listed at $3.679 per gallon. Since I ended up buying 11 gallons, the E10 saved me around $4. At first glance, the only obvious enhancement is the enhancement of the price!

A sign at a local gas station touts the supposed benefits of ethanol-free pure gas.

A sign at a local gas station touts the supposed benefits of ethanol-free pure gas.

Based on the unit price it seems obvious there is an initial savings benefit to choosing the E10 ethanol treated gasoline. However, do you really see a financial benefit when all is said and done? Ethanol has about 25% less energy content than gasoline, so adding this substance dilutes the ability of the fuel to fire the pistons and gives your engine less bang for the buck. Consequently, due to this energy density reduction, there is a chance you will actually get fewer miles per gallon if you choose the ethanol enhanced fuel over an ethanol free grade like PureMax. Maybe the banner that proclaims you can save 25% on gas mileage is right.

So, does the ethanol infused E10 provide a financial enhancement over an alcohol-free option like PureMax just by being cheaper or is the upfront savings lost due to the inferior gas mileage of the fuel? To get to an answer, we need to calculate the number of miles per dollar of gasoline purchased, or miles per dollar (MPD). Just for fun, I decided to conduct an experiment to determine the MPD of both the E10 and the PureMax fuels to see if ethanol gasoline can truly be called enhanced or if the "No Ethanol" sign is right after all.

Gas nozzle for PureMax, a pure gas fuel offered by local filling stations

Gas nozzle for PureMax, a pure gas fuel offered by local filling stations

Ethanol Enhanced E10 Versus PureMax Pure Gasoline

To evaluate the effect of ethanol on miles per dollar or MPD I decided to run a little study using my own vehicle. I drove my 2008 Subaru Forester for several weeks using the ethanol enhanced 87 gasoline and recorded the mileage and fuel consumption. Then I switched over to the Puremax ethanol-free and monitored the same information. I ran the results through a statistical analysis called a two-sample t-test to determine if there truly was a performance difference between the two fuels. Finally, I calculated the miles per dollar.

During the experiment, I tried to keep my driving habits and patterns as consistent as possible. The driving represents a mix of highway and city driving, mostly on my commute to and from work. If I took a long highway trip on a certain tank of gas, I discarded that tank from the study.

Table 1 below shows the results for the E10 gasoline. The average gas mileage came out at 24.2 MPG and based on the recent cost of $3.299 per gallon; this gives a miles per dollar (or MPD) of 7.33.

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Table 2 contains the PureMax test results and shows the gas mileage at 25.8 MPG. With the recent cost per gallon of this fuel at $3.679, it ends up having an MPD of 7.01.

These results show that you can see a gas mileage boost of approximately 7% by using the pure gasoline instead of the E10, but based on current prices you end up getting penalized financially due to the higher cost as shown by the 4% drop in miles per dollar.

Table 1 - E10 Gas Mileage Results

TankMilesGallonsMPG

1

169.2

7.242

23.4

2

231.1

9.092

25.4

3

196.3

8.132

24.1

4

88.9

3.708

24.0

5

257.3

10.680

24.1

6

211.2

8.741

24.2

Total

1154

47.595

24.2

Table 2 - PureMax Gas Mileage Results

TankMilesGallonsMPG

1

276.2

11.247

24.6

2

298.7

11.561

25.8

3

294.4

11.063

26.6

4

275.5

10.81

25.5

5

201.0

7.581

26.5

Total

1345.8

52.262

25.8

The price per gallon for ethanol-free Puremax.

The price per gallon for ethanol-free Puremax.

The Bottom Line

My experiment showed that using ethanol-enhanced E10 fuel instead of the ethanol-free PureMax reduced my MPG by 6.2%, from 25.8 to 24.2 miles per gallon. However, because of its higher cost, the PureMax actually delivered 4.4% less MPD than the E10, 7.01 versus 7.33 miles per dollar, and turned out to be the worse choice from a cost perspective.

This financial benefit, however, depends on the price difference between the two grades. As the pure gasoline price approaches the E10 cost, a crossover point is reached where it actually becomes the better value in terms of MPD. With the results of this study, I came up with a guideline called “The 20 Cents Rule” that is easy to remember. It states that if the ethanol-free option costs 20 cents or more per gallon than the E10, then go with the E10, but if the difference is less than 20 cents then pure gas is the better value.

The other thing I learned is that you can't always believe what you read in advertisements. Since the pure gas delivered only a 7% increase in MPG instead of the "up to 25%" written on the banner. However, because of the lower overall cost of the ethanol enhanced E10 the ethanol does appear to provide a financial "enhancement" to the consumer.

Prices for the ethanol treated varieties of gasoline.

Prices for the ethanol treated varieties of gasoline.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2012 theframjak

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