Effect of 10% ethanol gas on automobile

Factual Questions
1

I have a 1997 Ford Contour, stick shift with the four cylinder engine. I’ve kept a detailed record of gas consumption for the life of the car, and had come to expect a gas mileage of generally 35 mpg each time the tank was filled.

A little exposition here. I drive on a very constant schedule, with roughly 95% freeway driving, and 5% city driving. The freeway driving is during the reverse commute, so speeds are constant at about 5 mph over the speed limit, with almost no use of the brake or clutch. In other words, about the easiest driving one can have on a car. As an example, there is now 148,000 miles on the vehicle, and its still on the original clutch, with its first brake (Notice? Brake, not Break!) job at 144,000 miles. The miles driven come out to about 400 every two weeks, which is the schedule on which I get gas. And my son-in-law owns an auto repair shop, so the maintenance schedule on the car is right what the manufacture says it should be.

Last September I noticed a sudden decline in gas mileage of from the 35 mpg to just above 32 mpg. And I started noticing those “Fuel may contain up to 10% ethanol” on the gas pumps. This level of gas mileage continued up to last May, when I found a station near work that sells ethanol free gasoline. I started using that station, with surprising results. I now have put five tanks of ethanol free gas into the car, and feel that this is enough data with which to draw some conclusions.

Average of the last ten tanks using 10% ethanol gas = 32.6 mpg, with a standard deviation of 1.6 mpg.

Average of the first five tanks using pure gasoline = 35.6 mpg, with a standard deviation of 1.08 mpg.

This is a mileage increase of almost 9%. This surprised me as calculating the BTU’s in 10% ethanol gas vs pure gas would indicate that one should get around a 4% increase.

I don’t think that the fact that the September - May stretch was during the winter was the cause as I have never noticed a similar dropoff during the winter. And here in the Great Pacific Northwest, there’s not that much difference between summer and winter temperaturewise.

The only thing that makes sense is that the ethanol gas is such crap that it knocks gas mileage even further than the reduction in BTU content would indicate.

I’ve started using ethanol free gas in everything gaspowered here. To find out where pure gasoline is sold in your area, log into Pure-gas.com, and click on your state.

Just threw this out as the sort of information that some of you Dopers might be interested in. Feel free to comment.

2

Your observations have been noted before by others, with numbers between 10% and 28% loss being noted.
Just Google:
ethanol lowers mileage

and you can read articles until the cows come home.

Bottom line, unless it’s over 10% cheaper than real gasoline, E10 is bad for your wallet.

3

It’s true ethanol contains less energy than gasoline. But your gas mileage dropped by 9% on a 10% ethanol blend, which means the ethanol would have to add virtually nothing to the pure gasoline blend.

Realistically pure ethanol should give you 20%-30% lower mileage than pure gasoline. With a 10% blend that translates to 2%-3% over a full tank.

Have you specifically checked your mileage for other September-May periods? There are other reasons mileage often drops in winter (e.g., winter vs. summer blends of gasoline, bad weather forcing you to drive in a lower gear, cooler temperatures meaning your tires are mildly uniderinflated and so on.)

4

Kunilou,

Losing 10+% of your gas mileage due to E10 is absolutely supported by every single one of the 4 articles I read before I answered the OP.
The reasoning given, when articles explored why the ethanol in E10 blends appears to do no good at all, was that modern computerized engine controls don’t cope perfectly with the change in combustion characteristics caused by ethanol.

5

I agree - on a pure “Rule of Mixtures” calculation, the expected mileage drop would be only 4%. So something else is going on here. And in my original post I discussed in sort of agonizing detail that I had noticed, over the 14 years I’ve owned the car, no discernable drop in mileage during winter. And I habitually keep my tires inflated up to the maximum recommended by the tire manufacturer.

As an editorial comment, its appearing to me that we are getting screwed by the insatiable desire of Congress to keep the votes coming in from the midwest farming states. And there doesn’t seem to be a thing we can do about it.

6

And my 2008 Honda Civic gets right around 35 mpg on either.

I drive around 300 miles per week, most of that a 50-mile round trip commute to work during rush hour. Fill up once a weekish.

I tracked my mpg for several months, then switched to pure gas and tracked for several more.

The difference in mpg was negligible. I’ve switched back to the blended because it’s usually 10-15 cents cheaper.

OTOH, we run only pure gas in our two older cars, based on our mechanic’s recommendations.

So mileage most definitely does vary on this issue.

(Not that I’m a proponent of ethanol fuel under the current system. It’s stupid and should be discontinued. But for many reasons other than the effect on MPG in use.)

7

Daylate,
A common refrain from forum discussion is that E10 is effectively cash being transferred from the pockets of the US consumer to corn farmers with the incidental side effect of raising global food prices.
You’re not the first, or even the ten-thousandth person to have that thought.
If we want to explore that, we could open a GD thread.

8

Couldn’t car engines be less able to efficiently utilize the ethanol mix? The decreased efficiency may not be directly related to the difference in caloric energy.

9

The maximum pressure stated on the tires is not a recommendation, it’s a safety limit. Recommended tire pressures are provided by the vehicle manufacturer.

10

Good thread on the tire pressure thing from 2003: