Can I use E85 in my Prius?

It’s the age-old question.  Can I use E85 fuel in my Prius?  Those of us who bought a hybrid did it for multiple reasons.

1. Save Money by buying less gas.
2. Save The Earth by using less gas.
3. Be Smug.

I don’t pretend not to be smug and neither should you.  It IS after all the right thing to do.

Now if you’ve gone this far to use less gas why shouldn’t you go 85% more and use Ethanol?  Would you not think the Prius should be a greener vehicle by being Flex-Fuel compatible?  I certainly would.  You can never be TOO green.  Unfortunately Toyota has decided NOT to be flex-fuel at this point and I think I understand why:

I own a 2008 Prius and drive it gently because it is fun.  There is a real-time fuel consumption display and an average consumption meter.  The more gently you accelerate and the longer you brake the more electric power you use instead of gas.  I average about 54 miles per gallon and you WISH you got that in your SUV don’t you?

Since using less gas is a good thing I decided to put half a tank of E85 in my car whether it is approved or not.  I enjoy scientific experimentation so I sometimes throw caution to the wind.  When my tank reached the halfway point I pulled in to a nearby station and filled it up to full with E85 which was selling for $3.08 compared to $3.75 for regular.  It took about 5 gallons since the Prius has a 10 gallon tank.  I estimate that since regular gas is already 10% ethanol, five gallons of 85% ethanol should give me a whole tank rated at about 47% ethanol.  And yes, you can use higher percentages of ethanol in a regular engine safely if it is a relatively new car.

The “catch” with using E85 is that there is less energy in a gallon of ethanol compared to a gallon of gasoline.  I found this hard to comprehend with normal thinking and really didn’t believe it.  Of course, it’s the human way to not believe facts until we have experienced them first hand.

Now the real-world results:
The engine ran perfectly normally.  I did not notice any less power nor did I get any warning lights.  Right away I DID notice that the real-time MPG readout seemed a bit lower than normal.  It was too soon to be sure anyway.  After a few days of driving on 47% ethanol I found that it was very difficult to get my average MPG to read over 50.   I reset it a few times trying different conditions.  After about a week and half of driving I was back down to half a tank.  My gauge read my average of 49 MPG.  That pretty much sums it up.

In conclusion, you CAN use some E85 in your tank but you will actually reduce your mileage a bit.

 10 Gallons of Gasoline  540 Miles  $37.50 Full Tank  6.28 cents per mile
 5 Gallons Gasoline & 5 Gallons Ethanol  490 Miles  $34.15 Full Tank  6.96 cents per mile
 Difference  50 Miles  $ 3.35  Savings per tank  0.68 less cents per mile

Saving 7 tenths of a cent per mile doesn’t matter so much.  It would take a LOT of miles to be a significant savings.  I don’t know the facts on whether there will be any long-term damage but I doubt it since engine parts are already made to withstand 10% ethanol.  Still, for the tiny diference in cost, it’s not worth the risk.  I guess you just can’t get around basic physics no matter how hard you wish.

So the reason hybrids do not use E85 is so that the mileage numbers will be maximized.

You could ALSO look at it the other way:  It’s only costing you .68 cents more per mile to pollute the world a little less.  That’s not such a bad thing.  If we could only get some reliable confirmation about whether or not there will be any damge done to the fuel system.  I might pay the extra just to save the planet a little.

I sure hope the car companies can improve engine technology to be able to get more from less.   I personally would like to see less powerful vehicles with smaller engines.  You really don’t need that much power no matter how brainwashed you are.

I’m glad to see that hybrids and electric vehicles are starting to catch on.  Let’s hope that gas prices stay high so the world will change for the better.



6 thoughts on “Can I use E85 in my Prius?

  1. Another Prius Driver

    Thanks for the datum. How certain are you that you maintain the same gentle driving? Regardless, the data is useful.

    By the way, E85 means there is 85% gasoline not ethanol. Your mixing solution resulted in 12.5% ethanol.

    1. I am very conscious about how I drive. It’s like a game.
      Actually It’s the other way around. According to wikipedia, “E85 is and ethanol fuel blend of 85% denatured ethanol fuel and 15% gasoline…” That doesn’t mean my calculations are completely correct but it is a close approximation. I seem to have lost the ability to do math. Thanks for your response!

  2. Denise Sacks

    Any news per Prius and E85, I have gotten excited to do so after exposure to “Alcohol Can Be Fuel” website and want to get going with this per Prius and Highlander… The cost of Oil is much higher then the dollar numbers!

  3. Anonymous

    Thanks so much for the post, this was very helpful. I just finished watching PUMP and had to find out if my Prius was Flex Fuel compatible. I plan to call Toyota directly to find out for sure. I will post if they tell me anythng helpful.

  4. Mac

    Well done on “throwing caution to the wind”, your boldness is appreciated. I have recently “buzz clicked” on my understanding of methanol and ethanol fuels. I came to this understanding more through the back door, from the conspiracy theorists perception of the world, and PUMP was very informative. Obviously we must create sustainable and local production methods. I’m glad to be the wiser. Fortunate to be the wiser. I’m taking my Prius to the station right now. Unbelievable.

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