Got my alcohol sensor installed and my e85 enabled tune uploaded to my truck on Sunday. Getting a reading of 8.6-9.0% of ethanol currently with about 1/8 of a tank left. I plan on filling up the tank when the fuel light goes on and I only have around 1 gallon of gas left to see what the e85 content of the station closest to me is on the sensor as well as with a tester. Then I'll have to wait and see if it ends up being worth it in terms of fuel economy on e85 vs premium gas around here.
Experimenting with E85
- Thread starter A_Harman
- Start date
I'm late to this party but... The octane measurement isn't that simple, unfortunately. If E85 is 105 AKI and is blended 50/50 with a 93 octane pump fuel, the result will not be 99 octane.
The motor octane of E85 is rather low, somewhere around 85. The RON is ~105, with the frequent calculated number I see of ~96 AKI. (R+M / 2 method) However, it will take the abuse of a 116+ AKI race fuel.
Ethanol (and methanol) reduces detonation in 2 ways. The first way is the very high heat of vaporization, which when calculated for stoichiometry gives us....
Gasoline = 9.7 BTU/lb of air
Ethanol = 39.9 BTU/lb of air
Methanol = 78.5 BTU/lb of air (because why not add another data point)
Ethanol is able to pull >4x more heat out of the intake air compared to gasoline, and this cooling effect results in a lower chamber temperature at the time of ignition. Lower chamber temperature means less detonation risk.
The 2nd way is ethanol's laminar flame speed, which is ~30% faster than gasoline. The flame front propagates across the chamber faster with ethanol, which means the end gases ahead of the flame front don't have as much time to heat up and auto-ignite.
The above 2 properties are why it's nearly impossible to get an accurate octane rating for ethanol in a CFR engine.
The motor octane of E85 is rather low, somewhere around 85. The RON is ~105, with the frequent calculated number I see of ~96 AKI. (R+M / 2 method) However, it will take the abuse of a 116+ AKI race fuel.
Ethanol (and methanol) reduces detonation in 2 ways. The first way is the very high heat of vaporization, which when calculated for stoichiometry gives us....
Gasoline = 9.7 BTU/lb of air
Ethanol = 39.9 BTU/lb of air
Methanol = 78.5 BTU/lb of air (because why not add another data point)
Ethanol is able to pull >4x more heat out of the intake air compared to gasoline, and this cooling effect results in a lower chamber temperature at the time of ignition. Lower chamber temperature means less detonation risk.
The 2nd way is ethanol's laminar flame speed, which is ~30% faster than gasoline. The flame front propagates across the chamber faster with ethanol, which means the end gases ahead of the flame front don't have as much time to heat up and auto-ignite.
The above 2 properties are why it's nearly impossible to get an accurate octane rating for ethanol in a CFR engine.
I road-tripped over the Memorial Day weekend, running about 1300 miles, and 4 tank fills.
May 27 Morning fill-up.
Filled with 13.3 gallons of E85 @ $4.32/gallon.
Residual in tank was 2.3 gallons of 33% E85.
Total E85 in tank: 14.0 gallons.
Proportion E85=90%
Fuel economy of previous fill (33%) was 377.5 miles / 13.3 gallons = 28.4 mpg @ $4.30/gallon.
Cost per mile = 15.1 cents
May 27 Afternoon fill-up.
Filled with 6.0 gallons E85 @ $4.29, 6.3 gallons 87 @ $4.49.
Residual in tank was 3.3 gallons of 90% E85.
Total E85 in tank: 9.0 gal.
Proportion E85=58%.
Fuel economy of previous fill (90%) was 328 miles/12.3 gal = 26.7 mpg
Cost per mile = 16.2 cents
Stayed in Louisville at the Beatles festival for 3 days.
May 30 fill-up.
Filled with 4.1 gal E85 @ $4.20, 7.1 gal 87 @ $4.40.
Residual in tank was 4.4 gallons of 58% E85.
Total E85 in tank: 6.7 gal
Proportion E85 = 42%
Fuel economy of previous fill (58%) was 337.2 miles/11.2 gal = 30.1 mpg
Cost per mile = 14.6 cents
May 31 fill-up.
Filled with 3.9 gal E85@$4.30, 6.1 gal 87@$4.80 (Now that's a very hurtful price increase!)
Residual in tank was 5.6 gallons of 42% E85.
Total E85 in tank: 6.25 gal
Proportion E85=40%
Fuel economy of previous fill (42%) was 296.0 miles/10.0 gal = 29.6 mpg
Cost per mile = 14.6 cents
Fuel economy dropped about 10% on the 90% E85 tank, and cost per mile increased, despite the lower cost per gallon.
Min cost per mile was on the 42 and 58% tanks. The 33% tank had slightly higher cost per mile.
The big jump in the price of 87 today will change the economics toward running higher percentages of E85. I'm saving a maximum of about 10% in cost per mile, and 87 octane just went up 9%, so most of that savings is lost. If I lose 10% fuel economy running straight E85, I'm basically wasting money buying 87 at anything more than a 10% price difference.
I had a problem with the 90% E85 tankful: The Check Engine light came on and stayed on until halfway through the 58% tankful. I didn't have my code scanner with me, so I couldn't check it. This issue will be something to think about if I have to run straight E85.
May 27 Morning fill-up.
Filled with 13.3 gallons of E85 @ $4.32/gallon.
Residual in tank was 2.3 gallons of 33% E85.
Total E85 in tank: 14.0 gallons.
Proportion E85=90%
Fuel economy of previous fill (33%) was 377.5 miles / 13.3 gallons = 28.4 mpg @ $4.30/gallon.
Cost per mile = 15.1 cents
May 27 Afternoon fill-up.
Filled with 6.0 gallons E85 @ $4.29, 6.3 gallons 87 @ $4.49.
Residual in tank was 3.3 gallons of 90% E85.
Total E85 in tank: 9.0 gal.
Proportion E85=58%.
Fuel economy of previous fill (90%) was 328 miles/12.3 gal = 26.7 mpg
Cost per mile = 16.2 cents
Stayed in Louisville at the Beatles festival for 3 days.
May 30 fill-up.
Filled with 4.1 gal E85 @ $4.20, 7.1 gal 87 @ $4.40.
Residual in tank was 4.4 gallons of 58% E85.
Total E85 in tank: 6.7 gal
Proportion E85 = 42%
Fuel economy of previous fill (58%) was 337.2 miles/11.2 gal = 30.1 mpg
Cost per mile = 14.6 cents
May 31 fill-up.
Filled with 3.9 gal E85@$4.30, 6.1 gal 87@$4.80 (Now that's a very hurtful price increase!)
Residual in tank was 5.6 gallons of 42% E85.
Total E85 in tank: 6.25 gal
Proportion E85=40%
Fuel economy of previous fill (42%) was 296.0 miles/10.0 gal = 29.6 mpg
Cost per mile = 14.6 cents
Fuel economy dropped about 10% on the 90% E85 tank, and cost per mile increased, despite the lower cost per gallon.
Min cost per mile was on the 42 and 58% tanks. The 33% tank had slightly higher cost per mile.
The big jump in the price of 87 today will change the economics toward running higher percentages of E85. I'm saving a maximum of about 10% in cost per mile, and 87 octane just went up 9%, so most of that savings is lost. If I lose 10% fuel economy running straight E85, I'm basically wasting money buying 87 at anything more than a 10% price difference.
I had a problem with the 90% E85 tankful: The Check Engine light came on and stayed on until halfway through the 58% tankful. I didn't have my code scanner with me, so I couldn't check it. This issue will be something to think about if I have to run straight E85.
Last edited:
June 3 fill-up.
9.7 gal E85@$4.50, 3.7 gal 87@$5.00 (Another painful price increase, and in only 3 days. This time, both E85 and 87 went up.)
Residual in tank was 40% E85. (.9 gallons)
Total E85 in tank: 10.6 gal
Proportion E85=68%
Fuel economy of previous fill (40%) was 388.1 miles/13.4 gal = 29.0 mpg
Cost per mile = 15.9 cents (Increased because of the higher cost of 87)
I decided to increase the proportion of E85 because the price of 87 was more than 10% higher than E85, but I didn't want to run pure E85 to avoid the CEL I got on the 90% tankful. In 105 miles of driving yesterday, the CEL didn't come on with the 68% E85 fill. Someday, I'll put this data in Excel and make a plot of %E85 vs mpg.
9.7 gal E85@$4.50, 3.7 gal 87@$5.00 (Another painful price increase, and in only 3 days. This time, both E85 and 87 went up.)
Residual in tank was 40% E85. (.9 gallons)
Total E85 in tank: 10.6 gal
Proportion E85=68%
Fuel economy of previous fill (40%) was 388.1 miles/13.4 gal = 29.0 mpg
Cost per mile = 15.9 cents (Increased because of the higher cost of 87)
I decided to increase the proportion of E85 because the price of 87 was more than 10% higher than E85, but I didn't want to run pure E85 to avoid the CEL I got on the 90% tankful. In 105 miles of driving yesterday, the CEL didn't come on with the 68% E85 fill. Someday, I'll put this data in Excel and make a plot of %E85 vs mpg.
Last edited:
June 7 fill-up.
12.5 gal E85@$4.80, (When will it end?)
Residual in tank was 68% E85. (2.1 gallons)
Total E85 in tank: 14.6 gal
Proportion E85=94%
Fuel economy of previous fill (68%) was 326 miles/12.5 gal = 26.1 mpg
Cost per mile = 17.8 cents
25 miles after filling up, the Check Engine Light came on. It did this over the Memorial Day weekend when I ran 90% E85.
12.5 gal E85@$4.80, (When will it end?)
Residual in tank was 68% E85. (2.1 gallons)
Total E85 in tank: 14.6 gal
Proportion E85=94%
Fuel economy of previous fill (68%) was 326 miles/12.5 gal = 26.1 mpg
Cost per mile = 17.8 cents
25 miles after filling up, the Check Engine Light came on. It did this over the Memorial Day weekend when I ran 90% E85.
Finally got below 1 gallon on Sunday and went to fill up my truck with E85. It was $4.499 a gallon vs $5.599 a gallon for premium, so there was about a 20% difference in cost. The question will be how much of a fuel economy hit will my truck take and if it will be worth it overall. I tested the alcohol content with my tester and it was about 80% vs the 72% I was getting in my data logging software HP tuners from the alcohol sensor. That does seem about right though with a little less than a gallon of 9% premium gas that was left in the tank. I don't drive all that much long distance anymore so it will probably take a few weeks before I will be able to figure the cost per mile. I'll post an update when I'm getting ready to fill up again.
One thing I have noticed already with E85 is that my truck definitely idles better with it, both by feel and by the timing not jumping around as much in the data log. Seems these engines like E85 from what other E85 users on gm trucks forums have reported as well.
One thing I have noticed already with E85 is that my truck definitely idles better with it, both by feel and by the timing not jumping around as much in the data log. Seems these engines like E85 from what other E85 users on gm trucks forums have reported as well.
Fuel cost per mile may be about equal with premium. 20% less fuel cost than premium, 20% less fuel economy. So far, that's the way from my experience. The sweet spot seems to be running 87 as the base fuel, and mixing 30-50% E85 to get the octane up to 92 or above.
I was wondering where you were getting the ethanol reading. My Actron code reader doesn't have an ethanol content parameter, and I looked at Scan Gauges, too.
June 9 fill-up.
9.5 gal 87@$5.20
Residual in tank was 94% E85. (6.1 gallons)
Total E85 in tank: 5.7 gal
Proportion E85=36%
Fuel economy of previous fill (94%) was 229 miles/9.5 gal = 24 mpg
Cost per mile = 20 cents
I knew by the time the gauge reached 1/2 tank that the fuel economy was lousy, so I short-filled it at 5/8 tank to get the E85 percentage down into the 30's.
The Verano gets ~30mpg on premium for $5.80 per gallon, which is 19.3 cents per mile.
If I'm getting 24 mpg on straight E85 for $4.80 per gallon, that's 20 cents per mile. No economic benefit there.
I checked the fault code that has been popping up on straight E85: P0171, Bank #1 Lean O2 Sensor.
9.5 gal 87@$5.20
Residual in tank was 94% E85. (6.1 gallons)
Total E85 in tank: 5.7 gal
Proportion E85=36%
Fuel economy of previous fill (94%) was 229 miles/9.5 gal = 24 mpg
Cost per mile = 20 cents
I knew by the time the gauge reached 1/2 tank that the fuel economy was lousy, so I short-filled it at 5/8 tank to get the E85 percentage down into the 30's.
The Verano gets ~30mpg on premium for $5.80 per gallon, which is 19.3 cents per mile.
If I'm getting 24 mpg on straight E85 for $4.80 per gallon, that's 20 cents per mile. No economic benefit there.
I checked the fault code that has been popping up on straight E85: P0171, Bank #1 Lean O2 Sensor.
I use HP tuners Scanning program, it has the ability to read the alcohol sensor and display it. It can pretty much display all sensor info, you just have to select it as one you want in the read out or graph areas.
Depending on what I end up getting in my mileage, I may end up switching to doing something similar to what you are doing. I can also tune the PCM so I may make some changes to the fueling and timing to try to improve my power and mileage as well.
June 13 fill-up.
4.25 gal E85 @ $4.70
8.6 gal 87@$5.40
Weighted cost per gallon = $5.17
Residual in tank was 36% E85. (.99 gallons)
Total E85 in tank: 5.24 gal
Proportion E85=34%
Fuel economy of previous fill (36%) was 363.3 miles/12.85 gal = 28.3 mpg
Cost per mile = 18.4 cents
4.25 gal E85 @ $4.70
8.6 gal 87@$5.40
Weighted cost per gallon = $5.17
Residual in tank was 36% E85. (.99 gallons)
Total E85 in tank: 5.24 gal
Proportion E85=34%
Fuel economy of previous fill (36%) was 363.3 miles/12.85 gal = 28.3 mpg
Cost per mile = 18.4 cents
E85 is the biggest scam ever perpetuated on the american people... Sure let's pay 12% less than regular gas for 20% worse fuel economy... makes as much since as our Gov't...
My last e85 fillup was $3 / gallon
E10 - $4.69
Seems like it’s worth it purely because n cost
June 16 fill-up.
5.1 gal E85 @ $4.70
7.6 gal 87@$5.40
Weighted cost per gallon = $5.12
Residual in tank was 34% E85. (1.0 gallons)
Total E85 in tank: 6.1 gal
Proportion E85=39%
Fuel economy of previous fill (34%) was 391.5 miles/12.7 gal = 30.8 mpg
Cost per mile = 16.8 cents
Very good fuel economy on this fill, from a BP station instead of Speedway.
5.1 gal E85 @ $4.70
7.6 gal 87@$5.40
Weighted cost per gallon = $5.12
Residual in tank was 34% E85. (1.0 gallons)
Total E85 in tank: 6.1 gal
Proportion E85=39%
Fuel economy of previous fill (34%) was 391.5 miles/12.7 gal = 30.8 mpg
Cost per mile = 16.8 cents
Very good fuel economy on this fill, from a BP station instead of Speedway.
Yes, if you get it at 20% less cost or lower than your normal fuel, it would be cost-effective.
Now that I have a good number of tank fills with different percentages of E85, it's time to plot the data:
I've been concentrating on fills in the range of 30-40%, but the data points are sparse between 50-90%. In the interest of science, I should fill that region out.
I'll be updating the chart from time to time as I gather more data.
I've been concentrating on fills in the range of 30-40%, but the data points are sparse between 50-90%. In the interest of science, I should fill that region out.
I'll be updating the chart from time to time as I gather more data.
June 20 fill-up.
7.05 gal E85 @ $4.60
5.97 gal 87@$5.10
Weighted cost per gallon = $4.88
Residual in tank was 39% E85. (1.01 gallons)
Total E85 in tank: 8.1 gal
Proportion E85=52%
Fuel economy of previous fill (39%) was 368.4 miles/13.02 gal = 28.3 mpg
Cost per mile = 18.1 cents
Increased the E85 to get more data points above 40% on the graph. Will be increasing to 60, 70, and 80% in the next few fills.
7.05 gal E85 @ $4.60
5.97 gal 87@$5.10
Weighted cost per gallon = $4.88
Residual in tank was 39% E85. (1.01 gallons)
Total E85 in tank: 8.1 gal
Proportion E85=52%
Fuel economy of previous fill (39%) was 368.4 miles/13.02 gal = 28.3 mpg
Cost per mile = 18.1 cents
Increased the E85 to get more data points above 40% on the graph. Will be increasing to 60, 70, and 80% in the next few fills.
Good data so far. Maybe add some E0-E30 data as well to fill out that end of the graph along with the 50-70 range. I'm interested to see the range of MPG you end up with. So far I can definitely tell my truck is getting less mileage but seems to have more power overall using E85. I just don't drive enough like you to get data like this in a timely manner.
If he tracks economy he likely has e10 data albeit with premium fuel
If he is tuned for premium it’s unlikely he will want to do 20% or less.
The fact a linear progression of Ethanol percentage vrs mpg follows a curve is both interesting and expected
Proves out the vapor nflection point.
Based on that “curve” 30-50% appears the be the sweet spot with increasing percentages being “less efficient “
Last edited:
Here is an interesting web site I found while searching for average fuel prices:
I entered the fuel price data from my last fillup and my annual expected commuting miles to see what savings the E85-friendly site would predict for my fuel cost:
It is interesting that the calculator predicts a 22.5% decrease in fuel economy, and that my annual fuel cost would increase ~$150 by running E85. My recent fill with 94% E85 gave me fuel economy of 24 mpg, which is close to what the E85prices calculator predicts. At least they're not trying to oversell E85 by making ridiculous claims about fuel economy.
I entered the fuel price data from my last fillup and my annual expected commuting miles to see what savings the E85-friendly site would predict for my fuel cost:
It is interesting that the calculator predicts a 22.5% decrease in fuel economy, and that my annual fuel cost would increase ~$150 by running E85. My recent fill with 94% E85 gave me fuel economy of 24 mpg, which is close to what the E85prices calculator predicts. At least they're not trying to oversell E85 by making ridiculous claims about fuel economy.
Yes. My Verano Turbo recommends premium fuel, minimum 91 octane. I would run down to 25% E85 with 87, but haven't done it yet. Once I get done running the swing up in E85, maybe I'll run a couple of tanks of 93 and 50/50 93/89 to recheck my baseline. I think of par value for fuel economy to be 30 mpg on premium and don't recall getting more than 32 mpg since I bought the car.
Similar threads
