E85 fuel

E85 fuel typically results in a lower fuel economy compared to regular gasoline, generally around a 15-27% reduction in miles per gallon. This is because E85, which is 85% ethanol and 15% gasoline, has less energy density per gallon than gasoline, meaning it takes more fuel to travel the same distance.

If the factory allows for use of E85 it is designed for its use for a certain amount of time.

Do you intend on keeping the car for longer than that (100k miles or so)?

IMHO for the marginal gains in fuel economy the long term damage and accelerated corrosion tot the entire fuel system is not worth it.

Remember, all components have a finite life. Even though the factory is rating the fuel system for use with E85 doesn't mean long term service life is not reduced.

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This is because E85, which is 85% ethanol and 15% gasoline

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Pump e85 is typically in the 65-70% range. I’ve never found true 85% that didn’t come in a drum from a race shop.

IWNUI*

I
Would
Not
Use
It

*Maybe in a rental car that was approved for it’s use?

Typically? It does. Basic thermodynamics. Ethanol has significantly lower heating value than gasoline. That’s one reason why cars can’t meet fuel economy figures shown on the car’s sticker.

In the right car, E85 can act as race fuel. It burns cooler so in a car built for both boost (turbo or , supercharger, blower) and E85 you can turn the boost up and get significant power increase over 93 Octane gasoline with proper tuning. However, you need quite a bit more E85 to do so and it requires bigger fuel injectors and fuel pumps.

As mentioned before, it is hygroscopic. Not a bad idea to use it and rotate back to regular gasoline....your mileage won't be great with E85 as it has less energy density.

Less fuel mileage, more HP. Wait til tank is near empty, then fill up. Drive 8 - 10 miles for computer to detect the E85 fuel and adjust for its use. I never had half a tank of regular gas then finish filling up with E85.

Correct or not, you sold me.

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Is there a downside to using it? Less fuel mileage

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This

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Is there a downside to using it? Less fuel mileage, possible engine damage long term?

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Increased fuel consumption, but your vehicle will feel a little more responsive after a couple of E85 tanks - at least the GMC or Chevrolet V8s will once the computer and fuel system recognizes the fuel type. No damage if your vehicle is designed for it. A lot of GM trucks built from 2007-2015 are designed to run on either regular unleaded or any combination of regular and E-85. In those days they had a yellow gas cap if they were equipped to run on E-85 (or maybe green....can't remember). I think a lot of Ram trucks can do it too. Not as many Fords but they had some gas F-250s that could use either/or.

Careful - a lot of cars are not designed for anything beyond E10 or E15. I could put E85 in my Silverado with no issues, but I can't put it in our 4Runner. Your car has to be designed to recognize high ethenol content and adjust the ECM to compensate. I think there's also a change in the rubber/gasket compounds for the fuel system in the E85 motors but I'm not sure.

TBH I don't like running E85. I have 3-4 local gas stations that sell regular 87 unleaded E-0. My vehicles don't run faster with that stuff, but it they get way better fuel economy. Our Yukon and 4Runner easily get 23 or 24 on flat highway on E-0.....both would not get 21 on E-10 or E-15.