Katerina Swanson
Flex fuel is an alternative fuel source for cars, also known as E85, that blends ethanol and gasoline. Ethanol is a plant-based gas alternative that is renewable and cleaner than ordinary gasoline. It is usually made from corn, but can also be made from sugar. Flex-fuel vehicles have an internal combustion engine and are capable of operating on gasoline and any blend of gasoline and ethanol up to 83%. The benefit of a modern flex-fuel vehicle is that you can use any combination of gasoline and ethanol, and the vehicle's sensors will detect the blend and make the necessary changes.
Flex Fuel Characteristics and Values
| Characteristics | Values |
|---|---|
| Definition | Flex fuel is a term for a specific blend of ethanol and gasoline. |
| Alternative Name | E85 |
| Composition | 51% to 85% ethanol, depending on the season and region. |
| Seasonality | Ethanol content is reduced in winter to reduce problems with cold-weather starting. |
| Vehicle Compatibility | Buick, Chevrolet, Ford, and GMC offer flex-fuel vehicles. |
| Pros | More environmentally friendly and economical than traditional fuel. |
| Cons | Poorer mileage and potentially damaging to cars not designed for flex fuel. |
| Vehicle Identification | Yellow gas cap or yellow ring around the hole. |
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What You'll Learn
Ethanol-blended gasoline
However, there are also some drawbacks to using ethanol-blended gasoline. One concern is the potential for reduced fuel efficiency. Ethanol has lower energy content than gasoline, which can result in lower mileage for flex-fuel vehicles. Additionally, ethanol has a higher affinity for water, which can lead to water contamination issues in fuel systems. Another challenge is the potential for corrosion and engine damage due to the corrosive effects of ethanol and the stimulation of microbial growth at certain concentrations. To mitigate these issues, fuel additives like Biobor EB and Biobor JF have been developed to enhance performance and protect engines from the harmful effects of ethanol.
Despite the ongoing debates around the pros and cons of ethanol-blended gasoline, it remains a significant alternative fuel option, with more ethanol refining plants opening up and an increasing number of consumers purchasing flex-fuel vehicles.
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Flex-fuel vehicles and their engines
Flexible-fuel vehicles (FFVs) are based on dual-fuel systems that supply both fuels into the combustion chamber at the same time in various calibrated proportions. The most common fuels used by FFVs today are unleaded gasoline and ethanol fuel. Ethanol FFVs can run on pure gasoline, pure ethanol (E100) or any combination of both. Methanol has also been blended with gasoline in flex-fuel vehicles known as M85 FFVs, but their use has been limited to demonstration projects and small government fleets.
Flex-fuel vehicles use a sensor to detect the type of fuel being fed to the engine and adjust the combustion process accordingly. Modern flex-fuel vehicles are built using advanced technology such as electronic sensors. These technological advances allow the car to adjust its operation, including detecting the fuel blend and making any necessary adjustments. Many flex-fuel vehicles run on ethanol, which is sustainably produced from ingredients such as cane sugar and corn. This makes ethanol a good alternative to purchasing foreign oil.
In 2005, Volvo and Saab introduced flexifuel models to the Swedish market. Saab began selling its 9-5 2.0 Biopower, followed in 2006 by its 9-5 2.3 Biopower. Volvo introduced its S40 and V50 with flexible-fuel engines, followed in late 2006 by the new C30. In 2007, Saab also started selling a BioPower version of its popular Saab 9-3 line. In 2008, the Saab-derived Cadillac BLS was introduced with E85-compatible engines, and Volvo launched the V70 with a 2.5-litre turbocharged Flexifuel engine. In Brazil, FFVs are popularly known as "total flex" or simply "flex" cars. In Europe, they are known as "flexifuel" vehicles. Automakers, particularly in Brazil and the European market, use badging in their FFV models with some variant of the word "flex".
While flex fuel can be sustainably produced using corn and sugar, its production comes with a downside. Crops designed for flex-fuel production cannot be allocated to other sources, which could potentially drive up the price of animal feed. Corn is also susceptible to disease and weather conditions such as flooding and drought, which can affect corn prices during poor harvests. Ethanol also absorbs dirt easily, which can potentially corrode and damage engines.
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Pros and cons of flex fuel
Flex fuel is an alternative fuel made from a combination of gasoline and methanol or ethanol. Ethanol is made from plant materials, including corn, cane sugar, and other sugar sources. The most common form of ethanol-based gas is called E85, which contains 51% to 85% ethanol, depending on the season and region.
Pros of Flex Fuel
Flex fuel has several advantages for drivers, the nation, and the planet:
- Flex-fuel vehicles can burn whatever proportion of fuel mixture is in the combustion chamber. The vehicle's sensors will detect the blend and make the necessary changes.
- Ethanol burns cleaner than gasoline, which means flex-fuel cars pump fewer toxic fumes into the environment.
- Flex fuel contributes fewer greenhouse gases, making it a more environmentally friendly option than traditional gasoline.
- Flex fuel is sustainably produced and helps reduce reliance on foreign oil.
- Flex-fuel vehicles are eligible for tax credits, which can significantly reduce or even eliminate their tax obligation.
- Flex fuel is generally cheaper than traditional gasoline.
Cons of Flex Fuel
There are also some disadvantages to using flex fuel:
- Flex fuel is not as economical as gasoline, so it is less widely available at gas stations.
- Ethanol has corrosive effects on engines, especially with the additional moisture in E85 fuel.
- Flex fuel has lower energy content, which results in reduced mileage compared to regular gas-powered vehicles.
- Flex-fuel vehicles were once thought to be the future of automobiles but have since been overshadowed by hybrids and electric vehicles.
- The crops used for flex-fuel production could drive up the price of animal feed.
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E85 and its composition
Flex fuel is an automotive drivetrain that can run on either traditional or ethanol-blended gasoline. The most common form of ethanol-based gas is called E85. E85 is an abbreviation typically referring to an ethanol fuel blend of 85% ethanol fuel and 15% gasoline or other hydrocarbons by volume. In the United States, the exact ratio of fuel ethanol to hydrocarbon may vary from 51% to 83% ethanol, according to ASTM 5798. This is due to the lower heating value of neat ethanol, which makes it difficult to start engines in cold climates.
E85 was created primarily to take advantage of the United States' ability to produce bio-based ethanol, typically from corn. This had the dual effect of propping up domestic agriculture via subsidies and reducing reliance on imported oil. Ethanol can also be produced from other plant materials, including cane sugar. This makes ethanol a good alternative to purchasing foreign oil.
E85 is used in engines modified to accept higher concentrations of ethanol. In the US, flexible-fuel vehicles (FFVs) are designed to run on any mixture of gasoline or ethanol up to 85% ethanol. In warmer countries, such as Brazil, FFVs run on neat alcohol. The higher ethanol content in E85 can cause corrosion in engines not designed for it, especially due to the additional moisture in E85 fuel. Stainless steel fuel lines and fuel tanks are sometimes used to prevent this.
E85 has a higher octane rating than regular gasoline, allowing it to be used in higher-compression engines, which tend to produce more power per unit of displacement. The Koenigsegg CCXR, for example, has 20% more horsepower when using E85. The lower heating value of E85 also makes it a popular "power adder" in turbocharged performance vehicles, increasing power and torque while reducing GHG emissions.
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Flex-fuel availability
Flex-fuel vehicles (FFVs) have an internal combustion engine and are capable of operating on gasoline and any blend of gasoline and ethanol up to 83%. E85 (or flex fuel) is a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season.
E85 is not available at every filling station. In fact, only a small percentage of gas stations nationwide supply ethanol, although that is likely to change as more consumers purchase flex-fuel vehicles. The RFA states that E85 is available at more than 2,800 gas stations.
According to Experian, as of 2022, there were more than 20.9 million FFVs in the United States. Four automotive brands—Buick, Chevrolet, Ford, and GMC—offered FFVs in the 2025 model year. Additionally, Ford and General Motors currently offer full-size pickups and cargo vans that are compatible with flex fuel. According to the Renewable Fuels Association (RFA), more than 80 different models from eight manufacturers were available to consumers as recently as the 2015 model year.
Some signs that your car may be an FFV include a yellow gas cap, a yellow ring where you insert the fuel nozzle, or a badge with "Flex-Fuel", "FFV", or "E85" on the rear of the vehicle.
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Frequently asked questions
Flex fuel is a term for a specific blend of ethanol and gasoline. Ethanol is a plant-based gas alternative that is renewable and cleaner than ordinary gasoline. The most common form of ethanol-based gas is E85, which contains up to 83% ethanol content in the summer and less in the winter.
Ethanol is more environmentally friendly than the typical 90/10 percent gasoline/ethanol mix found at most pumps. It produces fewer greenhouse gas emissions, which helps slow the progress of climate change. Ethanol is also cheaper than regular gas, and consumers who drive flex-fuel cars receive tax credits.
Ethanol is harsher than gasoline, and it can dry out fuel lines, O-rings, and other plastic parts. If your vehicle is not designed explicitly for flex fuel, you should avoid using it. Flex fuel is also not as economical as gasoline, so it is less available at gas stations.
Many manufacturers put yellow gas caps on flex-fuel vehicles or a yellow ring where you insert the fuel nozzle. Other vehicles have labels on the fuel doors indicating they take flex fuel. You can also check your owner's manual or visit Fueleconomy.gov to learn how to identify a flex-fuel vehicle.
