Car care · Elgin Auto Sales & Service Center · Elgin, IL
What Is Flex Fuel? E85 and Flex-Fuel Vehicles Explained
Flex fuel is another name for E85, a high-ethanol blend that only flexible fuel vehicles (FFVs) are built to use. Here is what the U.S. Department of Energy's Alternative Fuels Data Center and fueleconomy.gov say about it, and how to tell whether your car can take it.
51% to 83%ethanol in E85, by geography and season
15% to 27%fewer miles per gallon on E85
Up to 10%ethanol in most U.S. gasoline
Yellow capcommon sign of a flex-fuel vehicle
The short answer
Flex fuel, or E85, is a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season, according to the U.S. Department of Energy's Alternative Fuels Data Center (AFDC). Only flexible fuel vehicles (FFVs) are designed to use it; fueleconomy.gov says FFVs can run on gasoline, E85 or any mixture of the two, and that they typically get about 15% to 27% fewer miles per gallon on E85 than on regular gasoline. If your car is not an FFV, use the fuel your owner's manual specifies.
E10, E15 and E85 compared
The number after the "E" is the percentage of ethanol by volume. Here is how the common blends compare, according to fueleconomy.gov and the AFDC:
| E10 | E15 | E85 (flex fuel) | |
|---|---|---|---|
| Ethanol content | Up to 10% | Up to 15% | 51% to 83%, depending on geography and season |
| Which vehicles can use it | All gasoline vehicles: all automakers approve blends up to E10 | Model year 2001 and newer gasoline vehicles (EPA, since 2011) | Flexible fuel vehicles only |
| Effect on miles per gallon | Typically 3% to 4% fewer than 100% gasoline | Typically 4% to 5% fewer than 100% gasoline | Typically 15% to 27% fewer than regular gasoline |
| Where you find it | Most gasoline sold in the U.S. | Pumps dispensing E15 must be labeled | Selected stations; see the AFDC station locator |
From Ethanol (fueleconomy.gov) and Ethanol Fuel Basics (Alternative Fuels Data Center), read November 9, 2026. Your owner's manual may list the maximum ethanol content the automaker recommends for your vehicle.
Is my car a flex-fuel vehicle?
Because FFVs look just like gasoline-only models, fueleconomy.gov says you may be driving one and not know it. The AFDC adds that, other than an ethanol-compatible fuel system and a different powertrain calibration, FFVs are similar to their gasoline-only counterparts. To check, fueleconomy.gov suggests you:
- Look for a yellow gas cap or a yellow ring around a capless fuel filler. Most manufacturers started using yellow gas caps on FFVs as of model year 2008 (2006 for General Motors).
- Check the fuel door: some FFVs have a label there indicating the fuel type.
- Check your owner's manual, which usually specifies which fuels can be used. If you do not have one, it may be on the manufacturer's website.
- Look for badges on the body with terms such as E85, Flex-Fuel or FFV.
If you cannot confirm your car is an FFV, use the fuel your owner's manual specifies rather than E85. Shopping for a used car? Ask us to show you the fuel door, and the owner's manual if available, on any car you are considering.
From Flex-fuel Vehicles (fueleconomy.gov) and Flexible Fuel Vehicles (Alternative Fuels Data Center), read November 9, 2026.
Mileage, cost and performance on E85
Ethanol contains less energy than gasoline. Fueleconomy.gov says ethanol has about one-third less energy than gasoline, and that because of ethanol's lower energy content, FFVs running on E85 get roughly 15% to 27% fewer miles per gallon than on regular gasoline, depending on the ethanol content. The AFDC says that other than lower miles per gallon, drivers of FFVs will see little difference when using E85 instead of gasoline.
On cost and performance, fueleconomy.gov notes:
- E85 is typically cheaper per gallon than gasoline but slightly more expensive per mile; its relative cost varies with location and energy markets.
- Drivers should notice no performance loss on E85, and some FFVs have more torque and horsepower on E85 than on regular gasoline.
- E85 can only be used in flex-fuel vehicles and is not sold at every station.
Ethanol also has a higher octane number than gasoline, according to the AFDC; lower-octane gasoline is blended with 10% ethanol to reach the standard 87 octane.
From Ethanol (fueleconomy.gov), E85 (Flex Fuel) (Alternative Fuels Data Center) and Ethanol Fuel Basics (Alternative Fuels Data Center), read November 9, 2026.
Service at Elgin Auto Sales & Service Center
Not sure what fuel your car takes, or have a fuel system question? Schedule service or see our service specials.
Our service department at 1200 E. Chicago St. in Elgin is open Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m., and is closed Sunday. Get directions.
Flex fuel FAQ
What is flex fuel?
Flex fuel is another name for E85, a gasoline-ethanol blend containing 51% to 83% ethanol depending on geography and season, according to the AFDC. It is meant for flexible fuel vehicles.
What is a flex-fuel vehicle?
Fueleconomy.gov says a flexible fuel vehicle (FFV) can run on gasoline, E85 or any mixture of the two. The AFDC says FFVs are similar to gasoline-only models except for an ethanol-compatible fuel system and a different powertrain calibration.
Can I put E85 in a regular car?
No. Fueleconomy.gov says E85 can only be used in flex-fuel vehicles. Use the fuel your owner's manual specifies.
How do I know if my car is flex fuel?
Look for a yellow gas cap or yellow ring at the fuel filler, a label on the fuel door, E85, Flex-Fuel or FFV badges, or the fuels listed in your owner's manual, as fueleconomy.gov suggests.
Does E85 get worse gas mileage?
Yes. Fueleconomy.gov says FFVs typically get about 15% to 27% fewer miles per gallon on E85 than on regular gasoline, because ethanol has less energy than gasoline.
Is E15 the same as flex fuel?
No. E15 contains up to 15% ethanol and is approved for model year 2001 and newer gasoline vehicles. Flex fuel (E85) contains 51% to 83% ethanol and is only for flex-fuel vehicles.
What are your service hours?
Monday to Friday 8 a.m. to 5 p.m. and Saturday 8 a.m. to 4 p.m. We are closed Sunday.
Shopping for a used car?
Visit us at 1200 E. Chicago St. in Elgin.
Sources
Fuel blend, flex-fuel vehicle and mileage information is from the U.S. Department of Energy's Alternative Fuels Data Center and from fueleconomy.gov, the U.S. government fuel economy site administered for the Department of Energy and the EPA, read November 9, 2026. This is general information; your owner's manual is the authority for your vehicle. Our address and service hours are from our own website, checked the same day. Photo is of our dealership.
- Flexible Fuel Vehicles (Alternative Fuels Data Center), U.S. Department of Energy, read November 9, 2026
- E85 (Flex Fuel) (Alternative Fuels Data Center), U.S. Department of Energy, read November 9, 2026
- Ethanol Fuel Basics (Alternative Fuels Data Center), U.S. Department of Energy, read November 9, 2026
- Flex-fuel Vehicles (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Ethanol (fueleconomy.gov), U.S. Department of Energy and U.S. EPA, read November 9, 2026
- Home page: address, Elgin Auto Sales & Service Center, read November 9, 2026
- Service page: service hours, Elgin Auto Sales & Service Center, read November 9, 2026