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  • E85 gasoline or flex fuel is an alternative fuel that uses a mixture of ethanol and gasoline.
  • Some advantages of using it include being more sustainable, improving performance, and having a higher octane rating.
  • Disadvantages of using flex fuel include vehicle incompatibility, potential engine damage, reduced fuel economy, and limited availability.

The type of fuel you use affects how well your car operates. The right type ensures your engine runs smoothly while preventing damage and maximizing fuel economy. And with different types of fuel available, it can be tricky to track how they fare against one another.

One fuel type that’s becoming popular is the E85 flex fuel.

What is E85 Gasoline?

E85 gas, also known as flex fuel, is an alternative fuel. It’s a mixture of 85% ethanol and 15% gasoline, but the percentage can vary, as some variants have 50% ethanol and 50% gasoline.

Why Does the Ethanol Percentage Vary?

It often depends on the geographical location and time of the year. The mixture usually has more ethanol during the summer compared to the winter because of these two reasons:

Volatility Control

Ethanol has different evaporation characteristics compared to gasoline. In warmer temperatures, more ethanol is added to the mixture to control the fuel’s volatility.

This also means that more gasoline needs to be added to the blend during cold weather, making E85 gasoline more expensive in winter.

Economic Factors

There are times when ethanol is cheaper than the petroleum component of gasoline, making it cost-efficient to add more of it to the mixture.

In fact, the summer of 2022 marks the highest ethanol blend rate in the United States. It reached 10.5%, which is the highest percentage since it was tracked in 2007.

Pros of E85 Gasoline

e85 gasoline pump
Many drivers prefer E85 gasoline because of the many benefits it offers.

Many drivers prefer E85 gasoline because of the many benefits it offers, from being better for the environment to improving performance and increasing octane ratings.

Better for the Environment

Flex fuel is better for the environment because it has a smaller carbon footprint and burns cleaner than traditional gasoline.

The mixed-in ethanol is also produced using renewable sources, such as corn and other biological materials. In short, E85 production releases fewer air pollutants into the atmosphere compared to some types of fuel.

More Sustainable

As mentioned, ethanol is made of corn and other biological materials. That makes flex fuel more sustainable compared to fossil fuel, which will eventually run out. After all, having a renewable alternative means prolonging our resources.

Less Dependence on Foreign Oil

In 2022, the US imported 8.3 million barrels of petrol from 80 countries daily. This increase contributes to inflation and unemployment in the country and could also significantly affect economic growth and the trade balance.

Using ethanol is a great alternative to purchasing foreign oil, mitigating the negative effects of importing fuel.

Better Engine Health

Ethanol is better for the engine because it has a thermodynamic cooling effect that keeps it cooler than gasoline. It also cleans the engine and other components better than gasoline, reducing the risk of carbon deposits.

Improved Performance

E85 gasoline can give vehicles a boost in power and torque. The enhancement stems from flex fuel having a faster ignition time and flame propagation compared to gasoline, leading to higher cylinder pressure.

In some cases, the engine could gain up to 20% with flex fuel.

Higher Octane Rating

Octane ratings are measures of stability based on the pressure fuel will spontaneously combust. It also plays a key role in engine performance and the ability to resist knocks, which happens when fuel burns unevenly in the engine.

Ethanol has naturally higher octane fuel compared to regular gasoline. The higher rating validates the advantages listed above, as E85 gasoline means improved performance and reduced carbon dioxide emissions.

For reference, E85 gasoline usually has an octane rating of 100-105, while most premium gasoline in the US carries 91-93.

Cons of E85 Gasoline

Of course, using E85 gasoline also has disadvantages, like vehicle incompatibility, potential engine damage, reduced fuel economy, and limited availability.

Vehicle Incompatibility

Traditional gas engines can’t use E85 gasoline.

So if you drive an older model and want to switch to flex fuel, you need to upgrade your car to support the alternative gas. This typically involves installing some form of fuel injector for fuel pumps.

Using the incorrect fuel type may lead to costly damage to the fuel lines.

Potential Engine Damage

Ethanol is naturally corrosive because it absorbs dirt easily. This issue can result in storage problems, water issues, and engine damage over time. It could also degrade rubber and plastic parts in the engine and fuel line, both of which are costly to repair.

Reduced Fuel Economy

Ethanol contains less energy per volume than gasoline, so you’ll get fewer miles per gallon. For reference, flex fuel vaporizes 30% to 35% faster than traditional gasoline.

The only upside is that E85 gas is typically cheaper per gallon than premium gasoline, so you won’t feel the reduced economy as much.

Limited Availability

Some areas don’t have access to E85 gas because they’re produced from corn and other biological materials. As such, you’ll find stations that offer flex fuel more abundant across the Midwest.

Thankfully, flex-fuel vehicles can use any combination of gasoline and ethanol and make the necessary changes to the blend.

Costlier Vehicle Parts

Flex fuel vehicles have more expensive parts because they can run both E85 or regular pump gas. This means repairs and replacement of certain worn components may cost more, because they’re more advanced.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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