E15 gasoline is a blend of 15 percent ethanol alcohol and 85 percent gasoline. It is approved in the U.S. for use in ALL 2001 and newer passenger cars and light trucks, and in any Flex-Fuel vehicle.
Prior to the introduction of E15, the maximum amount of ethanol allowed in ordinary pump gasoline was 10 percent. Under new EPA rules in 2019, gasoline refiners and retailers are allowed to sell gasoline that contains up to 15 percent ethanol for use in 2001 and newer passenger cars and light trucks. Blends that contain up to 85 percent ethanol (E85) are also allowed, but ONLY for use in FLEX-FUEL vehicles, not ordinary vehicles.
E15 motor fuel contains 50 per more ethanol than current gasoline (15 percent versus 10 percent). Ten percent ethanol is commonly used in reformulated gasoline, which is required in many large metropolitan areas to reduce air pollution. Ten percent ethanol (E10) is also commonly used in many premium grade 91 to 93 octane fuels as an octane booster. This improves the detonation resistance of the fuel and allows the use of higher compression ratios for better performance and fuel economy. NASCAR has been using E15 since 2012 in its race cars. With E15, the extra ethanol boosts the pump octane rating of the fuel several additional points compared to 10 percent ethanol gasoline. The pump octane rating may be as high as 98 with E15 if it is blended with a high grade gasoline, or as low as 91 to 93 octane if it is blended with a low grade gasoline. The actual pump octane rating will be determined by the refiners who supply the product.
It's a little less expensive than E10 or regular unleaded gasoline. Increasing the amount of ethanol in gasoline helps reduce the need for imported oil to make gasoline. Less demand for crude oil helps to counter the rising price of crude oil overall. Using more ethanol also helps support corn prices, which helps American farmers.
Ethanol burns cleaner than gasoline so it helps to reduce carbon deposits on pistons and inside combustion chambers. Using E15 keeps engines cleaner and running better.
The higher octane rating of E15 raises detonation resistance for a slight gain in performance in high compression engines. However, ethanol contains less energy per gallon than gasoline (76,100 vs 114,100 BTUs). The energy content of E15 is about 108,400 BTUs per gallon, so it takes more fuel to produce the same amount of energy. Consequently, you can expect to get about 1.5 to 2 percent FEWER miles per gallon with E15 compared to an E10 ethanol/gasoline blend.
As for cost, there should be no significant advantage or disadvantage. E15 should be priced somewhat less than E10 or straight gasoline due to the increased ethanol content. This essentially offsets the slight difference in fuel economy between the various grades of fuel.
As we all know, fuel costs can vary greatly from one day to the next (sometimes hourly!), and from one service station to the next. The price of gasoline and corn can also change abruptly and can be affected by politics, weather and supply and demand. So the pump price of E10, E15 and straight gasoline can vary quite a bit depending on how the oil companies, fuel distributors and service stations set their prices. Oil companies often mix ethanol with lower octane gasoline to raise the overall octane rating of the fuel. This gives the oil company a better profit margin per gallon but the trade-off may be a fuel that does not delivery quite as good a mileage.
E15 is not without controversy. Txtra concentration of ethanol in E15 may damage some rubber and plastic fuel system components in older vehicles. The risk is primarily for vehicles built prior to 1995. Since 1995, all fuel systems have been required to be made with alcohol-resistant materials. On 2001 and newer vehicles, the fuel systems are even more alcohol resistant and should experience no problems whatsoever.
One group who opposed the introduction of E15 was the Specialty Equipment Market Assn. (SEMA). This group opposed the introduction of E15 because they believed the fuel might harm rubber and plactic components in classic muscle cars, older hot rods and other vintage vehicles.
Congress established the Renewable Fuel Standards (RFS) in 2005 and then set ambitious goals in 2007 to mandate biofuel sales. The RFS rules led to the adoption of E15 blends for use in 2001 and newer vehicles. The main concern is what happens if E15 is accidentally used in older vehicles? There is a potential the extra dose of ethanol might harm rubber hoses, seals and plactic carburetor components IF the fuel system has not been upgraded with modern ethanol-resistant materials.
The EPA does require service stations to post a warning label (see the E15 warning label at the top of this article) to warn consumers NOT to use E15 in vehicles made before 2001, or in motorcycles or small engines (lawnmowers, snowmobiles, etc.).
Those who oppose the use of ethanol fuel blends say ethanol attracts moisture, and that may increase the risk of corrosive acids forming inside the fuel system. On the other hand, because ethanol attracts moisture, it also helps dry the fuel system to prevent gas line freeze during cold weather and other moisture-related problems. It also burns cleaner than gasoline to reduce carbon deposits in the combustion chamber and on pistons.
It depends on the year, make and model vehicle you drive and what the car manufacturer's warranty policy is with respect to E15. It should NOT be an issue with vehicles that are less than five or six years old, but for vehicles that are 10 or more years old, you should probably check with the car manufacturer if you have any concerns BEFORE filling up your tank with E15.
Though some studies have reportedly found that E15 can cause fuel system damage in some of these older fuel systems, extensive testing by the EPA and the Department of Energy on 2001 and newer vehicles has found that E15 causes no problems whatsoever.
Since 2019, the EPA has allowed Year-Round Use of E15. The EPA revised its rules that formerly restricted the use of E15 to winter months only as a means of reducing evaporative emissions. The updated rules allow E15 to be used year round provided the E15 blend meets the ASTM International 4806-10 standard for ethanol. In addition, its Reid Vapor Pressure (RVP) is limited to 9.0 pounds per square inch during the summertime gasoline volatility season (May 1 – September 15) so that MY2001-2006 motor vehicles can meet evaporative emissions standards with E15. Other seasonal and geographic requirements that limit the RVP of gasoline to lower than 9.0 psi still apply in areas that have a 7.8 psi summertime RVP standard.