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Flex Fuel or E85 Gas: Everything You Need to Know

Flex Fuel E85 Badge on 2009 GMC Yukon
Flex Fuel E85 Badge on 2009 GMC Yukon / Photo Credit: GMC

What Is Flex Fuel or E85 Gas?

E85 gas, or flex fuel, is gasoline that contains from 51% to 83% ethanol, according to the Environmental Protection Agency (EPA). Because cold weather affects combustion, the blend of gasoline and ethanol must be adjusted seasonally.

In other parts of the world, E85 specifically refers to a fuel mixture of 85% ethanol to gasoline (or equivalent hydrocarbon fuel). 

Pros & Cons of E85 Gas Over Regular Gas

The Pros of Flex Fuel:

1. E85 reduces greenhouse gas emissions.

The combustion of fossil fuels, such as gasoline, emits carbon dioxide, methane, and nitrous oxide – commonly referred to as “greenhouse gasses.” Flex fuels significantly lower the amount of fossil fuel being burned by the vehicle, which reduces the emissions overall. 

2. Vehicles running on flex fuel have less “knocking” and “pinging.”

E85’s higher octane helps improve the balance of air and fuel during combustion, which cuts down on the tendency for the engine to knock

3. Flex fuel/E85 gas keeps the engine clean.

Like most alcohols, ethanol is an effective cleaning agent, which means that the high ethanol content of a flex fuel blend can help keep the engine clean and even remove leftover deposits from lower-quality gasoline. 

4. Flex Fuel Vehicles (FFVs) give drivers more options at the pump.

Not every gas station across the country carries the exact same range of fuel options. An FFV can handle any blend of gasoline and ethanol, which means every station should have an option that works no matter where you are. 

Are you a first-time buyer and feeling a little overwhelmed? Our Tips For Buying Your First Car can help.

The Cons of Flex Fuel: 

1. Only FFVs can run on E85.

Regular gas usually contains 10% ethanol. In some parts of the country, stations offer gas with 15% ethanol, but that is less common. Many manufacturers don’t recommend blends over 10% for standard engines. 

Only vehicles designated for flexible fuel can run on E85 or any blends with more than 15% ethanol. Higher ethanol blends can damage standard engines. 

2. Ethanol releases more ozone.

A study by Stanford showed that vehicles running on higher concentrations of ethanol release more ozone. While ozone is fine when it’s high in the atmosphere, it can cause health problems when people breathe too much of it.

3. E85 reduces fuel efficiency.

Ethanol has about 30% less energy content than gasoline, which results in E85 having lower overall fuel efficiency. The EPA says that FFVs typically get 15 to 27% lower mpg on E85 compared to gasoline. 

For example: A 2020 Ford F-150 with a 5.0-liter V8 has a combined city-highway fuel economy estimate of 23 mpg with gasoline and 17 mpg with E85. The result is that driving 15,000 miles will cost $1,650 running on gasoline and $2,450 on E85 (based on current fuel prices).

Flex Fuel Station Featuring E85 Gas
Flex Fuel Station Featuring E85 Gas / Photo Credit: U.S. Department of Energy

What Is a Flex Fuel Vehicle or FFV?

A flex fuel vehicle (FFV) is one designed to run on a blend of gasoline and another fuel, usually ethanol (a plant-based alcohol). A typical flex fuel vehicle in the U.S. will run on a mixture as high as 17% gas and 83% ethanol, which is commonly called E85. 

Automakers have offered FFVs since the 1990s for several reasons:

  • Ethanol comes mainly from corn, a renewable energy source.
  • Ethanol produces lower greenhouse gas emissions than gasoline.

Can You Use Regular Gas in an FFV?

FFVs have an internal combustion engine and are capable of operating on gasoline and any blend of up to 83% ethanol.

How Can I Tell if My Car is an FFV?

In 2006, General Motors began using yellow gas caps for their FFVs, and since 2008, most automakers have done the same. Many FFVs also have a sticker on the fuel door or an exterior badge to indicate they are E85-compatible.

If you see any of these indicators, check your owner’s manual to confirm flex fuel compatibility. 

Yellow E85 Gas Filler on Ford Transit Van
Yellow E85 Gas Filler on Ford Transit Van / Photo Credit: Ford

Is Flex Fuel Better for Your Engine?

For flexible fuel vehicles, opting for E85 over traditional gas can help increase the life of your engine. This is due to the cleaning properties of the ethanol, which can prevent residue from building up. 

Will Flex Fuel Hurt a Conventional Engine?

It’s not recommended to use fuel with ethanol blends higher than 15% in a traditional engine. Some manufacturers even lower that recommendation to 10%.

Can E85 Gas Be Mixed With Regular Gas?

Yes. One benefit of a modern FFV is that you can use any combination of gasoline and ethanol. Your vehicle’s sensors will detect the exact blend and make the necessary changes.

How Does a Flexible Fuel Engine Work?

FFVs have an internal combustion engine, and most components are the same as those found in a conventional gasoline-only car. Some parts (such as rubber hoses or gaskets) will be more resistant to ethanol. Much of the difference between a traditional gas engine and an FFV comes from the computerized systems rather than the mechanical parts.

Is E85 Gas Good for My Budget?

E85 is generally cheaper at the pump than regular gasoline, so it will save money when you fill up. However, E85 is less efficient and burns faster, so you will need to refuel more often.

Additionally, the cleaner burning of high-ethanol blends may cut down on maintenance costs, which should also be factored into the calculations.  

Learn the Best Ways to Save on Gas.

Are FFVs More Expensive Than Conventional Vehicles?

While FFV engines are built differently than standard engines, those changes add little to the cost of manufacturing. This keeps the price of an FFV comparable in the market. 

Where Can I Buy a Flex Fuel Vehicle?

Most flex fuel vehicles are sold by domestic manufacturers such as Ford and Chevrolet, and many are pickup trucks. However, in recent years automakers such as Nissan and Toyota have offered FFVs as well.

What Happens if I Fill My Tank With 87 (Octane) Instead of E85?

It’s OK to use any octane fuel in an FFV engine. Their sensors will detect the level of ethanol and make the necessary changes for optimal fuel injection and timing of combustion. 

However, accidentally using E85 in an engine that isn’t designed to use it could cause mechanical issues or damage the vehicle’s fuel lines. Often, your engine warranty will also be voided. 

Easily keep track of your car’s maintenance schedule with the Carfax Car Care App.

If you have questions about this story, please contact us at Editors@carfax.com