E-85?

[clearlake outdoors]

I ran it when i could in the flex fuel truck i had.Truck idled smoother but took longer to start. Def a little more power. MPG dropped. I liked it pulling the trailer on hills.

[SoonerFan]

The service guy at the Chevy store told me that the 5.3 is made to run on either 100%, E-10, or E-85...just don't switch back and forth...pick one and stick with it.

[clearlake outdoors]

The flex fuel part of the manual says run it on any combination of e85 and gas

[gehol]

Yep

[pa.X19]

The service guy at the Chevy store told me that the 5.3 is made to run on either 100%, E-10, or E-85...just don't switch back and forth...pick one and stick with it.

If it doesn't have a yellow gas cap don't do this. Not all 5.3s are flex fuel. My wife's 09 Tahoe is, my 15 Silverado isn't.

[SoonerFan]

If it doesn't have a yellow gas cap don't do this. Not all 5.3s are flex fuel. My wife's 09 Tahoe is, my 15 Silverado isn't.

Sorry, little omission on my part.

[pa.X19]

[pitbully71]

Plus you get to pay extra, E-85 isn't a good financial move. Needs to cost at least 15-20% less than gas to even start to make things even.

This.

I did the math when I had my 2014 Silverado, I think I came up with 21% or something. Regardless, I've never seen it that much cheaper than regular E10-15. Ironically, E10-15 is some of the worst preforming fuel of all the blends in most cars (besides E85). The more Ethanol you put in, the worse it gets. With straight gas (zero Ethanol), I would always gain 2-3MPG in my '14 Silverado over the Ethanol blended fuels.

Above poster is also correct. If it doesn't have a yellow gas cap, its not a Flex Fuel. My new 2017 Sierra is not.

[SoonerFan]

I assumed that all cars and pickups were Flex Fuel these days.

[pa.X19]

I assumed that all cars and pickups were Flex Fuel these days.

So does your service guy Run !

[Bob G.]

If it doesn't have a yellow gas cap don't do this. Not all 5.3s are flex fuel. My wife's 09 Tahoe is, my 15 Silverado isn't.

My last 2 trucks with 5.3's had yellow gas caps, my 2018 w/5.3 doesn't have a gas cap at all.

[pa.X19]

My last 2 trucks with 5.3's had yellow gas caps, my 2018 w/5.3 doesn't have a gas cap at all.

Good luck putting gas in then JK.
I'm sure there's a designation badge or the 18s are all Flex fuel?

[kojimep]

I not aware of normally aspirated engines making more power on E85. Generally too low compression to utilize the E85. They are some turbo and supercharged engines that will boost manifold pressure when it detects E85 for increased power.

I stand corrected

The e85 map delivers more fuel to the engine, and significantly advances timing, that's how it makes more power, but at the same time does drop the mileage because you're using more fuel.

[pitbully71]

The e85 map delivers more fuel to the engine, and significantly advances timing, that's how it makes more power, but at the same time does drop the mileage because you're using more fuel.

E85 being 114 Octane doesn't hurt either!

[Bob G.]

Good luck putting gas in then JK.
I'm sure there's a designation badge or the 18s are all Flex fuel?

I've only had the truck for 3 months and still reach for the gas cap every now and then!! Last trucks had Flex Fuel badging and a window sticker. Will have to look at the manual.

EDIT: GMC website specs for my motor says that it is Flex Fuel capable.