Ethanol vs. Gasoline: MPG


Ethanol remains very popular as a ‘green’ alternative fuel to the terrors of gasoline.  Ethanol of course is nothing of the sort.  It causes more pollution and it decreases the fuel efficiency of your car.  The theoretical difference in mpg for even a 10% blend of ethanol is only about 3.7%, but over the course of a year it can easily add an extra tank or two, even with such a minor addition of ethanol.

I decided to put this to the test.  Over the past few months I have been filling up my car with a no ethanol blend of gasoline and then from stations that use up to 10% ethanol.  I did not verify that the fuel from the ethanol stations contained exactly 10% ethanol.  I also did the tests in series so all tanks of gasoline and then of ethanol were in sequence.  I also drove the tank to near empty each time.

I had to exclude several tanks of fuel because of exclusive highway trips or one tank that got used on a cold Halloween night.  The tanks of fuel that remained were all a normal mix of driving to work and around town.  There are no highway trips involved as a tank of all highway miles is very different than one with lots of city driving.  The average speed of each tank that was included was about 30 mph.  I was a bit surprised to see how consistent the overall driving was from tank to tank when it came to the average speed.

My average mpg when using gasoline was 18.6 mpg.  The predicted mpg of the 10% ethanol blend would have been 17.9 mpg and the actual was 18.0 mpg.  That is a pretty good result for a not tightly controlled experiment.  In everyday usage there was a difference.  There were times before I crunched the data that I wasn’t sure that the difference was there because it isn’t that noticeable in day to day usage with a 10% blend of ethanol, but when I did the comparison the 3.2% difference in the mpg showed up clearly.

The Inconvenient Skeptic

Even 10% ethanol is significantly less fuel efficient than gasoline without ethanol added.

In addition to getting less fuel efficiency I also added more ozone pollution to the valley air where I live as well as a variety of additional VOC’s.  In my location an electric car is certainly not an option in driving to work.  There were times when I went out to start my car at work that the temperature was less than 10 °F (-12 °C).  My car battery was not happy at those times and even told me so.  An electric car that sits in cold temperatures all day isn’t going to work well at all.

So the empirical data matches up well with the theoretical for the negative results of using a 10% blend of ethanol.  The difference in efficiency showed up in normal every day driving.  As I am done with the test I can assure my readers that I will only use ethanol blends if I am about to run out of gasoline.  Ethanol belongs in many places, but not in my gas tank.

Posted in Cap & Trade and Pollution by inconvenientskeptic on February 19th, 2011 at 3:08 pm.

3 comments

This post has 3 comments

  1. Stephen Brown Feb 22nd 2011

    I’ve only knowingly used ethanol once and that was in the 60s when I was at University in South Africa. I was in Durban with some friends, on holiday. We went out one evening partying. On the way home we ran out of petrol.

    We had a couple of bottles of Cane Spirit (colourless, potent drink made from sugar cane, goes well with Coke). The contents of the bottles went into the tank (it seemed to be a reasonable suggestion, at the time) and we drove to where we were staying without any problems.

    It still seems like a bit of a waste, though!

  2. inconvenientskeptic Feb 22nd 2011

    I will have a drink to toast the sacrifice you made to continue on your journey. :-)

  3. “An electric car that sits in cold temperatures all day isn’t going to work well at all.”

    You might want to write something about electric cars on your site. Perhaps you have somewhere but I have not found it.

    I live in Canada, and I hear a lot from people who want e-cars because they are cheap to run, but I say that they are really a rich man’s toy. My understanding is the Nissan Leaf is a small car that costs about $35k, and gets 160 km per charge. Not bad, but this might be under optimum conditions. In cold winter conditions the batteries will not hold a charge as well and of course the cabin MUST have heat. The batteries are the only source of power so cabin heat will drain the charge even further. I do not believe 160km driving distance will be the average for cold climates, it might be half that, but I have no evidence to support that claim.

    As time passes, the battery’s capacity to take a charge diminishes and must be replaced. This cost offsets the gas savings obtained from the previous years.

    I do not believe e-cars are economical at all. And this does not include the disaster of failed batteries occurring in blizzard conditions, potentially fatal.

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