E85 Question - Save $?

[JD S4]

Caveat - I know nothing about fuel.

I’m in an AutoTech and I live in CO where we only have 91. I’ve mixed in E85 (3 gallons) with a full tank of 91 since I purchased he car. I haven’t changed my mix drastically since adding the AutoTech.

Strange thought today that I personally had never thought of.

Why am I using 3 gallons of E85 and filling the rest with 91 —- when I could use something like 5 gallons of E85 and fill the rest with regular 85 octane fuel that is MUCH cheaper than 91.

Again, I don’t know anything about fuel. Is there a quality difference between pump 91 and pump 85 (not E85). If the real goal is to just land on an E#, say E25 - why am I not pumping more cheap E85 and then lowering the octane (and cost) on the rest of the tank?

Is there some property I haven’t thought about? Is everyone doing this and I’m an idiot and have been wasting $10 a tank on 91?

Thanks for the insights Fellas.


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[YotoWerks]

My A4 runs on full E85 with APR tune so it’s about $1 difference per gallon so a full fill up say 10gal is 35-40$ whole e85 is about 21$ so it’s almost 20$ per tank cheaper. The millage is about 5mpg less so it makes all the sense to me to run on E85 100% of the time.


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[JD S4]

My A4 runs on full E85 with APR tune so it’s about $1 difference per gallon so a full fill up say 10gal is 35-40$ whole e85 is about 21$ so it’s almost 20$ per tank cheaper. The millage is about 5mpg less so it makes all the sense to me to run on E85 100% of the time.


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That's different dialogue though. My question is am I being an idiot mixing 3 gallons of E85 vs. full tank of 91 instead of 5 gallons e85 and fill with 85 octane.

[Chris@EPL]

You do not want to do that. It is not just the ethanol. But also your tank is not fully completely mixed so you would probably be running some straight 85 some of the time and that would not be good. E85 is much denser and has a different consistency. You need more of the E85 to fire and having a small amount in the tank it is able to blend easily. Running a lot of E85 you may just get the 85 sitting on top of it. Stick with your 91 and 3-4 gals of E85.

[JD S4]

You do not want to do that. It is not just the ethanol. But also your tank is not fully completely mixed so you would probably be running some straight 85 some of the time and that would not be good. E85 is much denser and has a different consistency. You need more of the E85 to fire and having a small amount in the tank it is able to blend easily. Running a lot of E85 you may just get the 85 sitting on top of it. Stick with your 91 and 3-4 gals of E85.

This is interesting.. But also sounds like a bit of BroScience.

Are you suggesting that since 85 octane is less dense as a liquid - it would separate and sit "on top" of the E85 and effectively you'd run high levels of E85 part of the tank and then straight 85 on others? Or are you suggesting that since you don't get a perfect mix of fuels, you might be running 85 only and by using 91 you offer more "protection"?

Let's take this example. Completely empty tank.

You're saying that (example math) 5 gallons of E85 mixed with 9 gallons of 85 is "different" than 3 gallons of E85 and 7 gallons of 91 - even though both mix to net E25..

Again, example math. I'm just not good with "just do this because this is the way we do it"... Anyone else wnat to explain a bit deeper?

[Estoril4]

Not familiar with e85 but of curiosity, would this increase your chance of knock?

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[JD S4]

Not familiar with e85 but of curiosity, would this increase your chance of knock?

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per Chis response - it seems like it might? What he is suggesting is that since you don't get a "perfect blend" - when you're running 85 instead of 91 (even when mixed to the same E25 net) - you'd have more knock on the 85 when you got a mix issue.

[demonmk2]

If your car is not tuned for E85. you can mix it. Most of the stuff I've read is no more than 20% E85 to how many gallons of 91 gas you have. If you run above that and its not mixed good enough it can actually cause your engine to run lean since (its not tuned for it).

[JD S4]

lol. feels like guys aren't reading the thread or else I'm not explaining my question well.

[demonmk2]

https://www.bellperformance.com/blog/the-disadvantages-of-adding-ethanol-to-your-fuel

maybe this will help

If you add more e85 to gasoline no matter the octane and its not mixed properly you can run into problems. for the sake of the life of the vehicle I would do 20% e85 to how many gallons of 91 octane.

the less E85 you use it will mix better and less likely to separate and get some performance differences too.

[theweebabyseamus]

While part of it is bro science, I’ve always understood lower octanes to not be quite the same quality of fuel (there are many factors that can make a fuel ‘better’ other than octane, hence why sometimes you can gain power from race gas without tuning for it) but besides that, you would be lowering the octane of the tank as the non-e85 would be six points lower. For example, using 85/e85 at 13:3 would be 87.8 octane vs 92.6 octane if using 91 for the tank.

I’ve considered doing this for road trips as I use a full tank to get to SoCal and using 89 or even 87 would work since I grab a new tank when I get to my destination anyways. I haven’t tried it though.

Edit: when adding e85 you’re not targeting an E percentage, you’re targeting a higher octane number and taking the e85 percentage into account so you don’t hit the ‘ceiling’ of your fueling abilities, as you need to flow more e85 than regular fuel.

[TexasDfwS4]

Like what was said, if you aren't tuned for E gas your car can not adapt to the increase of full needed and you can run lean. I tried to push the E85 limit and the LPFP couldn't handle it. FYI Chris helps run one of the tuner company's used on this form so I would say that it's not BRO science.

[JD S4]

Like what was said, if you aren't tuned for E gas your car can not adapt to the increase of full needed and you can run lean. I tried to push the E85 limit and the LPFP couldn't handle it. FYI Chris helps run one of the tuner company's used on this form so I would say that it's not BRO science.

You didn't read what I was saying and I'm very aware who Chris is. Calm down cool guy - read it again.

[TexasDfwS4]

So what part did I miss?

[Chris@EPL]

It is also more of an issue of what the overall ethanol % is. Most cars you can not run more than about 4 gals without throwing a code. E content does not have anything to do with the octane. To put it easier if you ran a half a tank of 85 and a half a tank of 100 octane your overall octane would be 92.5, but you are also adding a much less quality 85 octane. Also not sure what your overall savings would be in the long run on a high performance car. I mean is it a $0.20 difference from 85 to 91, so on a fill up that takes 10 gals of 85 you would save $2. On these cars the octane in the tank needs to be correct and the Ethanol content also needs to be correct as well. Even if you can run 5-6 gals of E85 and the rest 85 octane, I really doubt that the car would run the same as your current mix of 91/E85.

Also the mixing is not a Bro science. I mean an ethanol test kit shows the Ethanol content separating from the rest of the gas/contents of the E85 fuel. Gas is even lighter than that, this is why is separates out and out are able to see the ethanol content on the test tube.

http://www.n54tech.com/forums/attachment.php?attachmentid=16004&stc=1&d=1383894965
Here you can see a pic of the E78 sinking to the bottom of the tube and the gas/rest of the fuel rising above it. They are much different densities and you need about 33% more E85 to fire and run the car which is also why the MPGs go down when you run more E85 versus gas. Same reason people got upset when the Govt started to add 10% ethanol to the fuel and caused minor decline in MPGs in cars.

[JD S4]

It is also more of an issue of what the overall ethanol % is. Most cars you can not run more than about 4 gals without throwing a code. E content does not have anything to do with the octane. To put it easier if you ran a half a tank of 85 and a half a tank of 100 octane your overall octane would be 92.5, but you are also adding a much less quality 85 octane. Also not sure what your overall savings would be in the long run on a high performance car. I mean is it a $0.20 difference from 85 to 91, so on a fill up that takes 10 gals of 85 you would save $2. On these cars the octane in the tank needs to be correct and the Ethanol content also needs to be correct as well. Even if you can run 5-6 gals of E85 and the rest 85 octane, I really doubt that the car would run the same as your current mix of 91/E85.

Also the mixing is not a Bro science. I mean an ethanol test kit shows the Ethanol content separating from the rest of the gas/contents of the E85 fuel. Gas is even lighter than that, this is why is separates out and out are able to see the ethanol content on the test tube.

http://www.n54tech.com/forums/attachment.php?attachmentid=16004&stc=1&d=1383894965
Here you can see a pic of the E78 sinking to the bottom of the tube and the gas/rest of the fuel rising above it. They are much different densities and you need about 33% more E85 to fire and run the car which is also why the MPGs go down when you run more E85 versus gas. Same reason people got upset when the Govt started to add 10% ethanol to the fuel and caused minor decline in MPGs in cars.

Responding to the above.

"E content does not have anything to do with octane" ---- that I didn't know. Hence the disclaimer that I don't know much about fueling.

"but you are also adding a much less quality 85 octane" --- this is what I'm wondering. Is this real? Is the 85 octane in my pump "worse quality" than the 91 next door?

"it is a .20 cent difference from 85 to 91" ---- it's like $1 difference here in CO.. You might save $5-$10 per tank and since we get worse MPG with E85 mix, I fill up 1-2 times per week. If $80/month doesn't matter to someone - they have too much money.

"the octane content needs to be correct and the octane content needs to be correct" --- this was my flaw in logic. I didn't understand them to be seperate values when it comes to how the car will run. I misunderstood that.

I see the pic - but how long would it take do seperate like that? I get the concept (who hasn't drank a black and tan!).

I have some gaps that I'm filling in here - mostly that e and octane *both* need to be right.. So by that logic - my 85/E85 blend doesnt work.

[jimrobbington]

lol. feels like guys aren't reading the thread or else I'm not explaining my question well.Lol should have used 87 octane as your example to reduce confusion haha

Very interesting conversation though. Also, to test E85 in a tube like that, you add water, which I believe accelerates the separation of the fuels due to ethanol absorbing the water and becoming heavier almost immediately.
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[USAF_Danny]

It is also more of an issue of what the overall ethanol % is. Most cars you can not run more than about 4 gals without throwing a code. E content does not have anything to do with the octane. To put it easier if you ran a half a tank of 85 and a half a tank of 100 octane your overall octane would be 92.5, but you are also adding a much less quality 85 octane. Also not sure what your overall savings would be in the long run on a high performance car. I mean is it a $0.20 difference from 85 to 91, so on a fill up that takes 10 gals of 85 you would save $2. On these cars the octane in the tank needs to be correct and the Ethanol content also needs to be correct as well. Even if you can run 5-6 gals of E85 and the rest 85 octane, I really doubt that the car would run the same as your current mix of 91/E85.

Also the mixing is not a Bro science. I mean an ethanol test kit shows the Ethanol content separating from the rest of the gas/contents of the E85 fuel. Gas is even lighter than that, this is why is separates out and out are able to see the ethanol content on the test tube.

http://www.n54tech.com/forums/attachment.php?attachmentid=16004&stc=1&d=1383894965
Here you can see a pic of the E78 sinking to the bottom of the tube and the gas/rest of the fuel rising above it. They are much different densities and you need about 33% more E85 to fire and run the car which is also why the MPGs go down when you run more E85 versus gas. Same reason people got upset when the Govt started to add 10% ethanol to the fuel and caused minor decline in MPGs in cars.

Hm weird.

I haven't logged my car with the two different types of fuel yet but I ran my car with different E85 from two different stations. Once with Ethanol free 91, and the other time was with 10% Ethanol 91. Car seems to run the same on both. I even tried to do a coolant bleed but on certain days, it feels like the car is struggling. Other times, it's a damn rocket ship. I'm getting the same MPGs now while mixing E85 than I was on straight 91 though. Something fishy is going on with my car.

[hilmar2k]

Hm weird.

I haven't logged my car with the two different types of fuel yet but I ran my car with different E85 from two different stations. Once with Ethanol free 91, and the other time was with 10% Ethanol 91. Car seems to run the same on both. I even tried to do a coolant bleed but on certain days, it feels like the car is struggling. Other times, it's a damn rocket ship. I'm getting the same MPGs now while mixing E85 than I was on straight 91 though. Something fishy is going on with my car.

Every forced induction car I've ever owned has been a bit Jekyll and Hyde. Slow as molasses one day, raped ape the next.

[theweebabyseamus]

Hm weird.

I haven't logged my car with the two different types of fuel yet but I ran my car with different E85 from two different stations. Once with Ethanol free 91, and the other time was with 10% Ethanol 91. Car seems to run the same on both. I even tried to do a coolant bleed but on certain days, it feels like the car is struggling. Other times, it's a damn rocket ship. I'm getting the same MPGs now while mixing E85 than I was on straight 91 though. Something fishy is going on with my car.

Ethanol free 91 and 10% (not always 10% btw) 91 octane are both 91 octane so there should be minimal difference. There’s a little improved cooling from the ‘10%’ of ethanol but it’s negligible at best I’m sure. Do you have cooling mods?

[Trent212]

If you are having issues paying for gas I'd suggest you get a daily that's suits your financial needs better than the s4, because the S4 is thirsty all the time. I was spending so much on gas/maintenance that I ended up getting an a3 to daily and keep miles down and save gas. Went from 20mpg on a good day to 34.

[JD S4]

If you are having issues paying for gas I'd suggest you get a daily that's suits your financial needs better than the s4, because the S4 is thirsty all the time. I was spending so much on gas/maintenance that I ended up getting an a3 to daily and keep miles down and save gas. Went from 20mpg on a good day to 34.

lmfao.. this is great.. thanks for the financial advice, Brother!

"A fool and his money are soon parted"

[TexasDfwS4]

The more E you run the more maintenance costs the creep up. The fuel pump has to run more and the fuel is more corrosive.

[Blue S4]

If you are having issues paying for gas I'd suggest you get a daily that's suits your financial needs better than the s4, because the S4 is thirsty all the time. I was spending so much on gas/maintenance that I ended up getting an a3 to daily and keep miles down and save gas. Went from 20mpg on a good day to 34.

This is such a terrible response. I commute 110 miles per day in my S4 and enjoy every fucking minute of it. I make enough money to justify the car, that's not the point.

I posted specifically in the EPL thread about actual, real-world MPG results when going full E85 and got so many dumb answers like yours "if you have to ask buy a different car". Over 25,000 miles per year, the price difference between 93 octane ($3.35 per gallon currently) and E85 ($1.85 per gallon currently) would make a drastic difference in my fill-up cost. I'm just trying to figure out how much it would actually impact the MPGs. I average about 28MPGs on the highway now doing 80mph according to the computer, but can easily get 330-350 miles on a tank without pushing it too far. Usually my calculated combined mileage is around 22MPG (even though the computer shows 24-25).

Separate issue, but some people actually like to commute in cool cars. I'm not showing up to the office in an A3 LOL

[theweebabyseamus]

The more E you run the more maintenance costs the creep up. The fuel pump has to run more and the fuel is more corrosive.

The fuel doesn’t corrode our fuel systems.

[saxon]

instead of asking why not just try it and do lots of logs

the beauty of this car is that the stock ecu can compensate pretty drastically if it detects knock

[mdwalsh20]

Definitely differences between fuel grades but even between the same grade but different brand... I don’t care and didn’t buy my car because of MPgs but anyone, no matter how much money they have, will be looking for ways to save that’s why the rich stay rich cuz they’re cheap as hell in many ways lol.. you can disagree on this but I found that shell V power here in CO gives me much better mileage per tank than other fuels of same grade.. so even though shell is roughly 20 cents more per gallon than other stations I get about 60 miles more per tank.. so .20 x 15 comes out to costing $3 more for a tank than say conoco but at 60 miles more per tank with an average of 20 mpgs comes out to about 3 gallons worth of fuel with the shell than other types, thus actually saving me about $6 per fill up after the $3 extra cost up front.


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[Trent212]

This is such a terrible response. I commute 110 miles per day in my S4 and enjoy every fucking minute of it. I make enough money to justify the car, that's not the point.

I posted specifically in the EPL thread about actual, real-world MPG results when going full E85 and got so many dumb answers like yours "if you have to ask buy a different car". Over 25,000 miles per year, the price difference between 93 octane ($3.35 per gallon currently) and E85 ($1.85 per gallon currently) would make a drastic difference in my fill-up cost. I'm just trying to figure out how much it would actually impact the MPGs. I average about 28MPGs on the highway now doing 80mph according to the computer, but can easily get 330-350 miles on a tank without pushing it too far. Usually my calculated combined mileage is around 22MPG (even though the computer shows 24-25).

Separate issue, but some people actually like to commute in cool cars. I'm not showing up to the office in an A3 LOL

I daily my TT RS most of the time, gets 25mpg and it's way cooler than my S4 would ever be lol, A3 is for when I have to cut back on the miles I put on it.

[street2gen]

instead of asking why not just try it and do lots of logs

the beauty of this car is that the stock ecu can compensate pretty drastically if it detects knock

This, watch your P3 for timing pull even.

[saxon]

This, watch your P3 for timing pull even.

You wouldn't be able to watch the timing on a p4, it's so dynamic youd jave no idea what it's supposed to be

[street2gen]

You wouldn't be able to watch the timing on a p4, it's so dynamic youd jave no idea what it's supposed to be

on a 3rd gear pull on the latter half of the rpm range its pretty stable.... I can at least tell that im pulling and a good idea of a range.
Of course log, but this would be a quick way to check after a fill up what the gas did.

[sb_gli]

On a tune designed for pump gas, if you mix more than a few gallons of e85, you risk running lean.

To elaborate on this:

To obtain lambda = 1 for ethanol, you need approximately 33% more ethanol than you would gasoline. The ECU will be able to adapt up to a certain percentage (up to 25% on the multiplicative trim) but beyond that, a lean code will be thrown and you run the risk of lamdba control being disabled and put your engine into a dangerous situation where it can run lean. I am not sure how the simos ecu handles situations where lambda control maxes out, but ME7 would completely cut out in some cases, causing an extremely lean condition halfway through a WOT pull. Dangerous!

When I tested a 3 gallon e85 mix on a full tank of 91 (w/ no added ethanol), multiplicative trims went from around +3% to +17-20%. I wouldn't want to run anymore e85 than what was in that mixture, and probably even less next time. I did, however, see big benefits of the e85 mixture even on the stock calibration. Timing pull was eliminated in almost all cases.

[FlyS4]

Why would you want to risk running lean and messing up your car for the fuel savings? That’s not a good strategy.

You need to get proper fuel to achieve consistent results and reduce the chance of a malfunction. Car needs more E85, it has less energy than gas. When you run that you will actually have bad gas mileage so when you think you are saving you will actually use more gas and pay the same or even more at the end. Hope that helps.


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[vpls4]

Doesn't the extra or modded tank pump and autotech hpfp help this situation? I thought that's why people were running these?

I have giac supplementary pump and autotech upgrades and I run e32 effective using e51/flex fuel, the only thing we have out here.

I mix 5.6 gals of e51 mixed with 4.8 gals of 91w/10%e which = e32.

No problems here and I drive it like a maniac.
Logs looked a lot better than when I ran e25, got my knk to under 2 and that's just a couple cyl's.

[FlyS4]

Doesn't the extra or modded tank pump and autotech hpfp help this situation? I thought that's why people were running these?

I have giac supplementary pump and autotech upgrades and I run e32 effective using e51/flex fuel, the only thing we have out here.

I mix 5.6 gals of e51 mixed with 4.8 gals of 91w/10%e which = e32.

No problems here and I drive it like a maniac.
Logs looked a lot better than when I ran e25, got my knk to under 2 and that's just a couple cyl's.

It does but I don’t believe he has those upgrades. He is just trying to save on gas by boosting his low octane gas (cheaper gas) octane level with e85.


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