So, it’s been about a month since I embarked on my ethanol fuel journey. I’ve gotten enough data points to be really confusing really quickly. However the app on my phone wonderfully keeps track of miles, gallons, prices and makes nice graphs. So…I’ll just use the graphing in my FuelLog app on my phone to show the trend, which is downward as expected, but not nearly as much as the internet would suggest.

## Methodology

First I started by filling up with E15, after a couple days of no problems and monitoring **Long-Term Fuel Trim**, I saw that my LTFT which normally runs around -8% was at -3%, not bad and it ran good. In an ideal environment LTFT should be 0.0%, or exactly at design parameters. Most vehicles actually run a bit negative, meaning the real world fuel metering is less than ‘design parameters’, and as carbon build up, engine wear and such become factors the trend is towards 0.0%. A LTFT number that is positive indicates the engine management is adding extra fuel, above design parameters to achieve a proper air to fuel ratio and clean emissions. Once the LTFT goes too high, the Check Engine light comes on and a Fuel Metering Lean diagnostic trouble code is set; what that limit is varies from vehicle to vehicle.

During the interim I have been reading more anecdotal evidences on the internet of people like myself that have decided to experiment with alcohol fuel. There was a handful of doom and gloom, ‘alcohol will destroy your vehicle’, then a handful of people with non-Flex-Fuel vehicles that ran straight E85 for 100,000 plus miles with no problems whatsoever. These were the outliers, the extreme ends. Most ran a mix that performed acceptably well, with reasonable fuel economy.

## The Experiment Begins

So I began topping up every day or two with E85 and driving with Torque running to monitor LTFT. With each fill-up the LTFT kept inching upward into the positive range. Finally at 17.3% the DTC P0171 – Fuel Metering Too Lean code was stored. I was also noticing that at wide open throttle, with the emission system falling into Open Loop, the engine power was down. Backing out of the throttle put the emission system back into Closed Loop and power increased. At this point I collected a sample and tested it with the shop’s fuel sobriety tester and found it to be 60% ethanol. I topped up with E10 and reset the Powertrain Contol Module with Torque, a second fuel sample was drawn and tested out at 35%. I ran out this tank without incident.

## A Mixture I Can Live With

Happily if you mix equal amounts of E15 and E85 you will arrive at a 50% ethanol mix. I generally buy 11 to 12 gallons of fuel if I wait until the low fuel light comes on to fill-up. So the plan was to put in 5.5 gallons of E85, then fill up with E15. On my first attempt at this I ended up putting in 7 gallons of E15 and by my math I had a mix of 43% which ran with no problems. The second tank I decided to go heavier on the E85 and topped up with a calculated blend of 53% mixed with a few gallons of the 43%, so I’m probably close to 50/50 at this time.

Over time I typically pumped 6 gallons of E85 first, then filled the rest of the way up with E15. My method for determining precentages is this. I add the gallons of E85 and E15 together, for example 5.519 gallons of E85, plus 6.661 of E15, equals 12.129 total gallons. Now I divide 5.519 E85 gallons by 12.129 gallons total; the result is 0.4550 or 45.5% ethanol.

The average I’m shooting for is 50%, so the next fill-up, knowing I have a couple gallons of lower than desired mix in the tank I put in 7.031 gallons of E85 and filled up the rest of the way with 5.491 of E15. Using the same formula, 7.031 plus 5.491 equals 12.522 total gallons. Dividing 7.031 by 12.522 equals 0.5614 or 56.1%.

## The Results

So…the graphing says that I am losing a little less than 1 mpg using a 50% ethanol blend. With a little fuzzy math looking at the chart I’ll say 20.5 mpg with E10 and 19.5 mpg with mixed fuel. So…am I saving money?

The simplest way I know to figure this is to take the total number of miles driven during this test 2,774, divide by a statistical 19.5 mpg for mixed fuel and 20.5 for E10 standard fuel and multiply both those figures by today’s prices. For the mix price I will use the average of today’s E15 and E85, because I was shooting for 50% anyway.

2774/20.5×2.17= **$296.34**

2774/19.5x(1.87+2.07/2)= **$280.25**

So yes, I did save $16 over the last month of testing. That number isn’t exact because of price fluctuations. Instead of diving into the minutiae of whether to calculate average daily price, actual price and so forth I chose to use current price, it’s close enough and compares the current price environment.

## Conclusion

I will probably continue to use a 50% blend. One of my stated goals in the last post was to reduce dependence on foreign oil, put U.S. farmers to work supplying fuel instead of paying those that hate us and fund terrorism.

Is this for everyone? No. Few people have the ability to accurately test their fuel’s sobriety, or access their vehicle’s data stream to make concise decisions. They are not a geek like me is what I’m saying. But it does illustrate that fairly modern vehicles will tolerate well in excess of the 10% the manufacturers warn against exceeding. I think it would be advantageous for manufacturers to produce more Flex-Fuel vehicles to reduce foreign oil dependency. I still do not know what the long term affects on my fuel system will be, but anecdotally modern vehicle fuel pumps wear well, modern fuel lines and seals are alcohol, or at least ethanol tolerant. We have seen no alcohol related failures in the Acura/Honda shop I work at on late model cars.

If you have the means of testing, aggregating data and are willing to take a risk, by all means go at it.

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