91 octane vs e85 in flex fuel Tahoe/suburban?

[iboughtatahoe23]

Which of these is better? I wanna save money of course but if 91 octane overall will increase longevity of the vehicle than by all means

Idk if it matters but the winters are harsh and the summers are hot here.

 

[swathdiver]

If you are doing it for cost, it depends on how many cents per mile it costs to run each fuel.

I would not run E85 during the winter, it ought to be E70 for winter but can still be hard to start.

The motors love E85 and take 5 tanks or so to get fully acclimated to it. The engine makes more power, idles smoother, cooler and even the transmission runs better. It's literally like cheap race gas. Oh, it's also a great injector cleaner.

When we are not planning to travel, we run E85. If we need the range, we run 93. I never intentionally run low octane fuel.

Here are the stats for my Yukon XL with the 5.3 motor:



You can see that for all city driving and 70% highway driving for a tank of fuel, the mpg difference is about 20%. Eventually, the faster you go the greater the spread between the two fuels cost wise.

 

[intheburbs]

There's no need to run 91 octane, unless you have the 6.2. Any benefit running a higher-octane fuel than what's required in your owners manual is a persistent internet myth that won't die. 5.3? Run 87 all day every day.

If you have a yellow gas cap, you can run E85, and you might notice a little more power from the engine. You'll also see a significant decline in mileage, likely greater than any cost save.

E85, or more specifically the alcohol in E85, is hygroscopic - meaning it absorbs water. So I would expect some long-term impact in terms of possible/likely increased corrosion in the engine due to the extra moisture.

 

[Marky Dissod]

Which of these is better?

What do YOU mean by 'better'? I know many 'kids' who are perfectly willing to pay MORE for E85 than for 87,
because E85 is moar powa, yo - plus it burns cleaner than petrol.

I wanna save money of course, but if 91 octane overall will increase longevity of the vehicle, then by all means

One of my close personal friends (a professional pcm / ecm / tcm tuner)
stopped paying for 91 octane once it cost 'too much' compared to 87.

My rile of thumb is that if E85 costs AT LEAST 17% less than 87 octane,
then it MAY be worth it to buy E85 instead of 87.
I.E.: In NYC E85 is nearly the same cost as 87, so I usually use 87.
In Long Island, E85 is cheaper by enough that I'll use E85.

Idk if it matters, but the winters are harsh, and the summers are hot here.

Unfortunately, E85 in the winter is E51 - it's only E85 (E83, actually) in the summer.
I wonder what it is in the spring and autumn?
In NYC, price relationship to 87 is pretty much the same year round, which is lame.