I bought my LE with the Flex Fuel option so that I would be able to run on it if the time comes but I have not tried it yet... it is available just down the road from me so I may give it a shot.
Anyone have experience with mileage and power differences? I would expect 20 percent poorer mileage and better power.

bump!;) Anyone?

my boss' '08 yukon is e85 compatible. he tried it on a couple long trips (its not avail here). he said he zeroed the trip computer after filling, and the tank of e85 averaged about 13mpg. on the trip home, with 87 octane, he got over 17.

my boss' '08 yukon is e85 compatible. he tried it on a couple long trips (its not avail here). he said he zeroed the trip computer after filling, and the tank of e85 averaged about 13mpg. on the trip home, with 87 octane, he got over 17.
That sounds about right...BUT...E85 octane rating is up around 107-109 so I would expect much better power. I am also toying with running methanol at a 50% mix since it is chemically very similar to ethanol but a little higher octane rating and a little more corrosive. But I would expect a flex fuel safe vehicle to be safe with a 50% mix. The main reason to run methanol for me? Price. $2.60 a gallon last I checked and 108 octane. Poorer mileage, but with the price savings per gallon, it may be worth it-- I will have to sit down and do the math.

I have the flex option as well, but have not done it. I've read here about people getting significantly worse mileage AND less power. With those characteristics, Ethanol should be at half the price as gas.

That sounds about right...BUT...E85 octane rating is up around 107-109 so I would expect much better power. I am also toying with running methanol at a 50% mix since it is chemically very similar to ethanol but a little higher octane rating and a little more corrosive. But I would expect a flex fuel safe vehicle to be safe with a 50% mix. The main reason to run methanol for me? Price. $2.60 a gallon last I checked and 108 octane. Poorer mileage, but with the price savings per gallon, it may be worth it-- I will have to sit down and do the math.

honestly, he didnt say anything about power. so i cant imagine it changed much for the better or worse. if there had been a change, i'd have heard about; i'm the one who told him to try the e85!

AAA does the weekly price average for gas and they then compute the cost of E85 compared to gas based on estimated loss in mpg - E85 is always much more expensive.......

Just something to think about

I have the flex option as well, but have not done it. I've read here about people getting significantly worse mileage AND less power. With those characteristics, Ethanol should be at half the price as gas.

I don't see how a higher octane rating could not positively affect power output... maybe it would take a dyno run to show it. But as for the loss of mileage, that is to be expected. I am still glad that I have the option to run alcohol since I actually purchased my '08-- I mean, its not a lease or anything... I think that alcohol is a fuel that will become more competitive in the future when people realize that burning up our food supply is just dumb. There is a lot of potential for making ethanol from non-food sources of biomass.

ran 2 tanks through last week. normal 87 cheapo gas I get 15 around town, 18 on the hwy with 275/70/18/e-series nitto grapplers at 50psi. With the E85 (15% 87 octane/85% 200 proof) I got 10 around town and 12 on the hwy. Noticeable loss of power and pickup.

bringing this back up...

anyone using this flex stuff? the last poster here said he had poor results... anyone have anything different?

also, if you are using regular gas and want to use flex, do you have to run your tank dry before you fill up with flex?

im asking this stuff for a friend who is thinking of trying it out on his mada...

I just bought my Armada and the first fill up was with E85. I will pump E85 for 2-3 months and post the results.

I have tried E85 3 times. All three times I have noticed a 3-4 mpg drop. It ran about the same as regular.

bringing this back up...

anyone using this flex stuff? the last poster here said he had poor results... anyone have anything different?

also, if you are using regular gas and want to use flex, do you have to run your tank dry before you fill up with flex?

im asking this stuff for a friend who is thinking of trying it out on his mada...

You can run any mixture/percentage that you want to of unleaded/ethanol in a flex fuel vehicle. The motor will adjust to any fuel ratio.
Power and mileage will decrease. Wear will increase since ethanol tends to strip lubricants from parts and it is corrosive as well. With the proper high quality synthetic oil this is much less of an issue, but maintenance intervals should be shortened for this reason. I like having the option since this will be a more legitimate fuel in the future-- not derived from corn.

Higher octane fuel doesn't mean more power. The higher the octane the slower the burn rate. This allows engines with higher compression/boosted to operate without detonation, and produce more power. However, using higher octane in an engine designed and tuned for a lower octane fuel won't give any significant power, if any.

thx guys.. i did some reading and got some knowledge on FFV... i personally dont see any benefit but again it was for a friend who was thinking of trying it out... ill refer him to this thread also so he can have a reference..

So in conclusion...it's not worth it?

from what i read and from here it seems not.. i have not seen anyone with a FFV armad say they had better overall results.

i also read these engines have to have a lower compression due to being able to use regular gas. ethanol has alcohol in it and in higher compression engines you get to benefit from alcohols high atomization. but these engines cant reap the benefits of that since they also have to have a lower compression for regular gas (i know i kinda repeated myself there) so SOME gas and MPG is reduced when using flex...

so it seems to me NO its not worth it in a hybrid engine like ours.. but a dedicated high compression engine it would be...