Experimenting with E85

[A_Harman]

July 21 fill-up.
6.3 gal E85 @ $4.30
7.3 gal 87@$4.80
Weighted cost per gallon = $4.58
Residual in tank was 31% E85. (.63 gallons)
Total E85 in tank: 6.8 gal
Proportion E85=44%
Fuel economy of previous fill (31%) was 374.6 miles/13.6 gal = 27.5 mpg
Cost per mile = 16.7 cents

Back to the 45% E85 series.

 

[LDM]

Finally got down to the point where I needed to fill up my truck today. After doing a little calculation, I came up with 23.129 gallons used with 201.2 miles. This comes out to a 8.70 mpg overall, almost all city driving with some hauling of stuff. Since I can usually end up with 10-12 mpg on premium in the summer when I don't take any longer trips, if I figure an average of 11 mpg normally, this means I lost about 21% fuel economy with E85. I paid $108.18 for the E85 at the last fill up for $4.499 a gallon while premium would have been $134.61 at $5.599 a gallon. Essentially that makes running E85 a wash since I paid about 20% less. Again, my numbers aren't 100% exact here either, since I'm estimated 11 mpg overall, it would go up or down from 10 to 12 mpg as the average. Unfortunately I don't travel like A_Harman does, so my data isn't going to be quite as useful as his.

Filling up today I was able to get E85 for $3.529, which I got 17.129 gallons for a total of $60.45. I ended up using 6 gallons of 87 octane added to the mix for a total of 23.129 gallons, of which I was able to get for free. However, I'm going to ignore that calculation as part of the E85 cost, and if I would have bought premium it would have been $5.179 a gallon for a total of $88.71. This is a difference of 32%, so running E85 with a 20% loss in fuel economy makes even more sense at this price.

My main reason for adding the 6 gallons of regular was to see if the truck gets any real improvement in mileage. I tested the E85 with my ethanol tester, it came out to 80% again. With the around 2 gallons I had left at 72% (1.44) alcohol content, 6 gallons of 87 with 10% (.6) alcohol content, and 17 gallons of E85 (13.6), that comes out to a total of 15.64 gallons of alcohol to the 25 gallons total, which ends up being 62.56% alcohol, down from the 72 it was overall last tank. This is almost perfect with my alcohol sensor in the truck, which is reading 62.7% after mixing everything up on the drive home.

I again don't plan on any long trips with my truck, so another 5-6 weeks from now I should have some more numbers. With E85 going cheaper, it seems like a good choice to run, especially since my truck does also seem to make more power overall from the datalogs. Seems to spend more time in V4 mode as well as having 10-15HP and TQ all across the board while running in V8 mode. And with the free 6 gallons of regular, I still come out with an octane of around 99-100 total, which is more than enough to meet the premium fuel requirement of 91.

 

[LDM]

So what does all this mean? At the end of all this data processing, am I saving money?
The data says yes:
View attachment 108397

Since I started running E85+87 blends on May 13, I have driven a total of 7879 miles (cell S2), and consumed 291 gallons (cell F2) of various blends at a total cost of $1334 (cell I2). Overall fuel economy has been 27.1 mpg (cell C1).

If I had been running premium gasoline all the time, assuming 30 mpg average fuel economy, I would have consumed 263 gallons (cell J1) at an assumed average cost of $5.62 (cell X3) for a total cost of $1477 (cell P1). The assumed average cost of premium is based on a 16% price increase between Regular and Premium.

So I have saved $143 fuel cost in two months. About 10%.

Hey 10% is a pretty good average of savings overall. I've found your information very interesting in this little experiment. I kinda wish I could contribute more than my very small data set but then again, with the price of fuel what it has been, I'm also glad that I don't drive 50K miles a year anymore. Well, if I was still doing that job it was in a company car, so I guess I wouldn't be paying for the fuel myself and could try out all of this as well. I drove a E85 capable Dodge Grand Caravan for that job so it would have been interesting to try this out with it as well.

 

[A_Harman]

July 26 fill-up.
5.7 gal E85 @ $4.20
6.7 gal 87@$4.70
Weighted cost per gallon = $4.49
Residual in tank was 44% E85. (1.4 gallons)
Total E85 in tank: 7.1 gal
Proportion E85=46%
Fuel economy of previous fill (44%) was 355 miles/12.4 gal = 28.6 mpg
Cost per mile = 15.8 cents

Continuing with the 45% E85 series.

 

[A_Harman]

Finally got down to the point where I needed to fill up my truck today. After doing a little calculation, I came up with 23.129 gallons used with 201.2 miles. This comes out to a 8.70 mpg overall, almost all city driving with some hauling of stuff. Since I can usually end up with 10-12 mpg on premium in the summer when I don't take any longer trips, if I figure an average of 11 mpg normally, this means I lost about 21% fuel economy with E85. I paid $108.18 for the E85 at the last fill up for $4.499 a gallon while premium would have been $134.61 at $5.599 a gallon. Essentially that makes running E85 a wash since I paid about 20% less. Again, my numbers aren't 100% exact here either, since I'm estimated 11 mpg overall, it would go up or down from 10 to 12 mpg as the average. Unfortunately I don't travel like A_Harman does, so my data isn't going to be quite as useful as his.

Filling up today I was able to get E85 for $3.529, which I got 17.129 gallons for a total of $60.45. I ended up using 6 gallons of 87 octane added to the mix for a total of 23.129 gallons, of which I was able to get for free. However, I'm going to ignore that calculation as part of the E85 cost, and if I would have bought premium it would have been $5.179 a gallon for a total of $88.71. This is a difference of 32%, so running E85 with a 20% loss in fuel economy makes even more sense at this price.

My main reason for adding the 6 gallons of regular was to see if the truck gets any real improvement in mileage. I tested the E85 with my ethanol tester, it came out to 80% again. With the around 2 gallons I had left at 72% (1.44) alcohol content, 6 gallons of 87 with 10% (.6) alcohol content, and 17 gallons of E85 (13.6), that comes out to a total of 15.64 gallons of alcohol to the 25 gallons total, which ends up being 62.56% alcohol, down from the 72 it was overall last tank. This is almost perfect with my alcohol sensor in the truck, which is reading 62.7% after mixing everything up on the drive home.

I again don't plan on any long trips with my truck, so another 5-6 weeks from now I should have some more numbers. With E85 going cheaper, it seems like a good choice to run, especially since my truck does also seem to make more power overall from the datalogs. Seems to spend more time in V4 mode as well as having 10-15HP and TQ all across the board while running in V8 mode. And with the free 6 gallons of regular, I still come out with an octane of around 99-100 total, which is more than enough to meet the premium fuel requirement of 91.

Since you ran almost all E85 in your first tankful, I would have guessed that you would get ~20% lower MPG. That's been my experience with the Buick. Fuel economy seems to fall off greatly above 70% E85. I think your fuel economy will be noticeably better on the 63% blend. 40-55% seems to be the sweet spot for lowest fuel cost per mile. It will be interesting to see as your data rolls up if your naturally-aspirated big V-8 has similar trends as my turbocharged little I-4.

The aspect of this fuel strategy that I like is that I am running fuel with higher octane than premium at a cost lower than regular.

 

[LDM]

Since you ran almost all E85 in your first tankful, I would have guessed that you would get ~20% lower MPG. That's been my experience with the Buick. Fuel economy seems to fall off greatly above 70% E85. I think your fuel economy will be noticeably better on the 63% blend. 40-55% seems to be the sweet spot for lowest fuel cost per mile. It will be interesting to see as your data rolls up if your naturally-aspirated big V-8 has similar trends as my turbocharged little I-4.

The aspect of this fuel strategy that I like is that I am running fuel with higher octane than premium at a cost lower than regular.

I believe I will end up trying something in the 40-55% range the next fill up. Hopefully both the price of E85 and regular continues to decrease in my area as it has the last month or so.

 

[A_Harman]

July 28 fill-up.
6.8 gal E85 @ $3.54
5.0 gal 87@$4.04
Weighted cost per gallon = $3.93
Residual in tank was 46% E85. (1.8 gallons)
Total E85 in tank: 8.6 gal
Proportion E85=55%
Fuel economy of previous fill (46%) was 336.6 miles/11.8 gal = 28.5 mpg
Cost per mile = 15.7 cents

I'm very happily surprised at the 56 cent per gallon fuel cost decrease!
Last of the 45% fuel fills. Very consistent mpg: 28.8, 28.6, 28.5.
New fill is stepped up to 55%, which I will do at least twice.

 

[Overfill]

I've always heard and seen the accounts of ethanol's very complete combustion and lacking tendency to leave deposits. If its my vehicle, and the $/BTU was commensurate with my needed resultant octane (which is how it seems to be priced 'round here anyway,) I would prioritize/choose to use as much of it as I can without throwing a CEL. I tried this in my forester for a very long time last year, and found it could tolerate a lot (IIRC E40 ish?), but never really needed that octane, and ultimately found it would burn well off reg E10. My ecoboost threw a CEL once I got to E30 aso IIRC, and I'd run UNL88 or mix to E20 for the above if I drove across Arkansas (even through it does just fine on 87). Have yet to see what max trim my bikes can do, but I imagine they'll be fine up to E20, and they need slightly high octane anyway.

 

[A_Harman]

August 1 fill-up.
5.9 gal E85 @ $3.50
5.2 gal 87@$4.00
Weighted cost per gallon = $3.79
Residual in tank was 55% E85. (2.5 gallons)
Total E85 in tank: 8.4 gal
Proportion E85=54%
Fuel economy of previous fill (55%) was 292.2 miles/11.1 gal = 26.3 mpg
Cost per mile = 17.0 cents

I'm not very happy with the fuel economy of the cheaper fuel.
It's the worst fuel economy of any fillup in the 50% range.
New fill is 54%, at the same gas station.

 

[Rmay635703]

Something I’ve noticed (even on lower ethanol percentages 15-20) Is that my fuel economy is dramatically affected by relatively small changes in temperature (aka even at 60F vrs 80F+, far more so than RUG

The ethanol winter math for me at least is different than summer so I keep that in mind for calculations

 

[A_Harman]

Something I’ve noticed (even on lower ethanol percentages 15-20) Is that my fuel economy is dramatically affected by relatively small changes in temperature (aka even at 60F vrs 80F+, far more so than RUG

The ethanol winter math for me at least is different than summer so I keep that in mind for calculations

I'm thinking winter will be OK for me in Michigan. The pumps have a sign posted saying the ethanol content can vary between 51 and 83% due to state law. I expect the 51% is for better cold starting ability. So I might be able to run straight E85, and not have to stand out in the wind and cold while I run two transactions to get the mix that I want.

 

[A_Harman]

August 3 fill-up.
5.9 gal E85 @ $3.60
5.0 gal 87@$4.10
Weighted cost per gallon = $3.82
Residual in tank was 54% E85. (2.5 gallons)
Total E85 in tank: 8.4 gal
Proportion E85=54%
Fuel economy of previous fill (54%) was 307.5 miles/10.9 gal = 28.2 mpg
Cost per mile = 15.3 cents

Better fuel economy on this tank.

 

[LDM]

Been doing a little more truck driving the last couple weeks and already down to 1/2 a tank. According to the lie-o-meter (what I like to call the MPG gauge in my truck on the center display) I'm getting around 11 MPG with 125 miles driven. This is already better than last fill up when at 1/2 a tank it was only 100 miles and just under 10 MPG. Note that the MPG gauge always seems to be off by about 1.5-2.5 MPG for some reason in my truck which is why I always hand calculate all my mileage instead of relying on it. I also spent a good 10 minutes trying to jump start another truck this week and I'm still getting better overall mileage with this 62% alcohol content. If I end up getting around 250 miles total out of this tank of gas and fill up right at 2 gallons left, that would be an estimate of around 10.86 MPG, which is a 2 MPG improvement over the 8.70 the last 72% E85 tank fill. Will update again on my next fill up with more accurate numbers than than extrapolation.

 

[Rat407]

Not sure if this was asked but those running close to 100% E85, has your tailpipe cleaned up? Not as much black on it as it would with using 100% gasoline?

 

[A_Harman]

Been doing a little more truck driving the last couple weeks and already down to 1/2 a tank. According to the lie-o-meter (what I like to call the MPG gauge in my truck on the center display) I'm getting around 11 MPG with 125 miles driven. This is already better than last fill up when at 1/2 a tank it was only 100 miles and just under 10 MPG. Note that the MPG gauge always seems to be off by about 1.5-2.5 MPG for some reason in my truck which is why I always hand calculate all my mileage instead of relying on it. I also spent a good 10 minutes trying to jump start another truck this week and I'm still getting better overall mileage with this 62% alcohol content. If I end up getting around 250 miles total out of this tank of gas and fill up right at 2 gallons left, that would be an estimate of around 10.86 MPG, which is a 2 MPG improvement over the 8.70 the last 72% E85 tank fill. Will update again on my next fill up with more accurate numbers than than extrapolation.

It looks like your fuel economy is improving significantly with the lower ethanol content.

I have also noticed my gas gauge isn't a good predictor of mpg. I look at the miles on the trip odometer when the gas gauge is at 1/4 tank, then calculate the mpg. It is usually about 2 mpg lower than I'm actually getting.

 

[LDM]

Not sure if this was asked but those running close to 100% E85, has your tailpipe cleaned up? Not as much black on it as it would with using 100% gasoline?

Yes, I notice a lot less black on my tailpipes from E85. I have a chrome dual tip borla on my truck and the black really shows and would need to be cleaned frequently. Apparenlty GM made these exhausts run extremely hot for emissions purposes.

 

[LDM]

It looks like your fuel economy is improving significantly with the lower ethanol content.

I have also noticed my gas gauge isn't a good predictor of mpg. I look at the miles on the trip odometer when the gas gauge is at 1/4 tank, then calculate the mpg. It is usually about 2 mpg lower than I'm actually getting.

This seems to be a GM thing as my 15 GMC sierra with 5.3 also was off on the MPG calculation. I can't find anything in the tune to make changes to for this so it must be calculated by something other than the PCM. BCM maybe? Either way GM seems to have programmed them to exclude certain data to give better MPG readout, probably to make people feel better about their fuel economy. I've noticed that it seems to be more accurate in the winter than in the summer as well and again, no idea why.

 

[Rat407]

This seems to be a GM thing as my 15 GMC sierra with 5.3 also was off on the MPG calculation. I can't find anything in the tune to make changes to for this so it must be calculated by something other than the PCM. BCM maybe? Either way GM seems to have programmed them to exclude certain data to give better MPG readout, probably to make people feel better about their fuel economy. I've noticed that it seems to be more accurate in the winter than in the summer as well and again, no idea why.

I use the Fuelly app to calculate mpg. I like it and easy to use.

 

[A_Harman]

Not sure if this was asked but those running close to 100% E85, has your tailpipe cleaned up? Not as much black on it as it would with using 100% gasoline?

I only have a couple of tank fills at 90% E85 or above. My overall average E85 content is 53%. I haven't noticed any reduction of carbon at the tailpipes. But I do notice a faint smell of distillery once in a while....

 

[LDM]

I only have a couple of tank fills at 90% E85 or above. My overall average E85 content is 53%. I haven't noticed any reduction of carbon at the tailpipes. But I do notice a faint smell of distillery once in a while....

Yes, my truck definitely has a very sweet smell every morning when I start it up and back out of my driveway. Do you get a lot of carbon build up on your exhaust? I'm curious if GM also makes the smaller engine vehicles run the exhaust hot like they do the V8s to try to lower emissions as much as possible.