E85 Usage

mtobeck · September 13, 2017

I know my truck definitely runs better on e85, but I'm lucky to even get 11mpg with it. That cuts total mileage per tank down by 100 miles and means much more frequent trips to the gas station (if you can find one that sells it). They sell e15 by me and its cheaper than 87 and get much better mpg.

TRKLGND · September 13, 2017

I know my truck definitely runs better on e85, but I'm lucky to even get 11mpg with it. That cuts total mileage per tank down by 100 miles and means much more frequent trips to the gas station (if you can find one that sells it). They sell e15 by me and its cheaper than 87 and get much better mpg.

I'm not sure how you get better mileage on E15 than regular unleaded. Ethanol contains less energy per unit then gasoline. It's not really possible to get better mileage.

Think about what you said, "cuts down total mileage per tank" then "gets much better mpg". "Much better MPG = MORE total miles per tank.

If I misunderstood you please forgive me.

mtobeck · September 13, 2017

I'm not sure how you get better mileage on E15 than regular unleaded. Ethanol contains less energy per unit then gasoline. It's not really possible to get better mileage.

Think about what you said, "cuts down total mileage per tank" then "gets much better mpg". "Much better MPG = MORE total miles per tank.

If I misunderstood you please forgive me.

I'm definitely getting higher mpg with e15 than with 87. Maybe it's due to the fact that it is e15+88 (sold at Murphy USA stations). I'm sure someone somewhere has studied the formula of e15+88 and knows the exact BTUs vs plain 87, that would be interesting to know.

And btw re-read my post. You're mixing things up. I said e85 cuts down on total miles per tank, and then I said e15 gives much better mpg vs e85, hence more miles per tank with e15. Sorry for confusing you.

TRKLGND · September 13, 2017

I'm definitely getting higher mpg with e15 than with 87. Maybe it's due to the fact that it is e15+88 (sold at Murphy USA stations). I'm sure someone somewhere has studied the formula of e15+88 and knows the exact BTUs vs plain 87, that would be interesting to know.

And btw re-read my post. You're mixing things up. I said e85 cuts down on total miles per tank, and then I said e15 gives much better mpg vs e85, hence more miles per tank with e15. Sorry for confusing you.

Octane has nothing to do with BTUs. It is a measure of resistance to detonation. E85 is 100 octane and contains about 30% less power than regular unleaded.

You are correct, I did misread your E85 statement.

mtobeck · September 13, 2017

Octane has nothing to do with BTUs. It is a measure of resistance to detonation. E85 is 100 octane and contains about 30% less power than regular unleaded.

You are correct, I did misread your E85 statement.

Hmm. Which could explain the lower mpg with 87. The computer probably detects too much knock with 87 and retards timing a bit, which causes more fuel to be injected. The e15+88 probably has a bit higher resistance to detonation to not cause timing to be retarded as much. Therefore, not injecting as much fuel. Thoughts?

TRKLGND · September 13, 2017

Hmm. Which could explain the lower mpg with 87. The computer probably detects too much knock with 87 and retards timing a bit, which causes more fuel to be injected. The e15+88 probably has a bit higher resistance to detonation to not cause timing to be retarded as much. Therefore, not injecting as much fuel. Thoughts?

Possible? Sure. But with a compression ratio of only 9.7:1 it would have to be some pretty poor 87 octane fuel. Maybe with 85 (reg unleaded in places like Colorado).

mtobeck · September 13, 2017

I remember seeing a post on here about someone suggesting not to run 87 with these engines due to knock, but I'll have to do some digging to find it.

Edit - these posts mention it:

http://www.gm-trucks.com/forums/topic/187631-run-a-tank-of-91-in-your-60/

http://www.gm-trucks.com/forums/topic/186574-premium-gas-in-a-53l-gmt900/page-2

http://www.gm-trucks.com/forums/topic/171043-what-type-gas-do-you-use-87-89-92/page-3

revrnd · September 14, 2017

I remember seeing a post on here about someone suggesting not to run 87 with these engines due to knock, but I'll have to do some digging to find it.

Edit - these posts mention it:

http://www.gm-trucks.com/forums/topic/187631-run-a-tank-of-91-in-your-60/

http://www.gm-trucks.com/forums/topic/186574-premium-gas-in-a-53l-gmt900/page-2

http://www.gm-trucks.com/forums/topic/171043-what-type-gas-do-you-use-87-89-92/page-3

For most of us our K2XXs are fairly new or not even broken in. I doubt there would be that much carbon build up in the cylinders (on the head & piston top surfaces) that would require the use of premium.

I think the price of 91 or 92 would put you in the poor house before you'd notice any performance or mileage gains in a motor designed to run on 87.

SierraHD17 · September 14, 2017

For most of us our K2XXs are fairly new or not even broken in. I doubt there would be that much carbon build up in the cylinders (on the head & piston top surfaces) that would require the use of premium.

I think the price of 91 or 92 would put you in the poor house before you'd notice any performance or mileage gains in a motor designed to run on 87.

The engine and trans though have been around since the 2007 model year though considering the only difference between the LY6 and L96 physically was the injectors used as the L96's are larger because of flex fuel.

Enough ignition timing and load and they will knock...

mtobeck · September 14, 2017

Premium is not required by any means on the l96, but it is with the 6.2L. Black bear performance says on their website that these engines don't run efficiently on 87. GM suggests at least 89 for 10:1 compression ratio and higher engines, 9.7:1 is not too far from that. I'd be willing to bet the ecu is retarding timing slightly with 87. I don't know why else I would be getting better mpg with a lower btu/gal fuel. I drive the same drive everyday. E15+88 is essentially 88 octane, so it may be a great option for efficiency and cost per mile with the l96, depending on the price in your area of course.

sdeeter19555 · September 14, 2017

I contacted Justin from Black Bear Performance about an E85 tune for my truck. As you may know, in factory spec, the 5.3 makes more HP & TQ on E85 than regular unleaded. The 6.0 does not. Justin tells me it is because the compression ratio of the 6.0 is much lower (9.7:1 vs 11.0:1). He does have an E85 tune available for the 6.0. However, I'm not willing to take a chance and void my power train warranty, I was really just asking out of curiosity.

That's good to know, I won't waste time looking for it now!

Sent from my SAMSUNG-SM-G900A using Tapatalk

TRKLGND · September 14, 2017

E15 is really hard to find around me. Only one independent station carries it. E85 is easier to find but neither is sold by any of the large players (BP, Shell or Marathon). They are oil companies after all.

I have never noticed a bit of knock, even when towing the boat. If it's there, the ECM is doing a good job retarding the timing. I'll use a few tanks of E15 and see what happens to my mileage. I noticed that it is priced the exact same as 87 unleaded (E10).

Not a single station around me carries pure gasoline.

SierraHD17 · September 14, 2017

You won't hear knock on a vehicle built in the last 20 or more years unless something is drastically wrong. The stock tune is such a sack you could probably run 80 octane fuel and get away with it. Custom tuning will make it happen.

Nick The Great · September 14, 2017

My '07 was Flex Fuel but I couldn't find any FFV when I bought my '17. Which is sad because I like E85.

My wife's '07 Impala was also a FFV and it had problems with E85. Her fuel pump started having issues, so we quit running it, and it cleared up. My impression was that GM didn't really put much thought into their FFV's at the time.

I don't understand why people bitch about the difference in MPG. It's a different fuel with different properties. A diesel truck could do 500 or 600 miles on a tank vs the 400 miles I get with gas. Vs 300 with E85. LPG or CNG is different yet.