E10 Ethanol and Fuel Mileage

Visit any of the internet discussion forums where ethanol is being discussed and you will always see someone claiming large decreases in fuel mileage with ethanol blends. The problem though with user testimonials is that there is no way to control the other variables that effect fuel mileage in normal day to day driving. That is why formal tests conducted under controlled conditions is the only way to truly measure the effects of ethanol blends on fuel mileage.

Some time back California decided that they needed to move to lower carbon fuels. The move to greater use of biofuels in the transportation sector was part of this strategy and in preparation they started conducting tests to determine how the expanded use of ethanol would effect emissions. One of the studies conducted also reported the effects of ethanol blends on fuel mileage.

Fleet average fuel consumption increased by 1.4% when ethanol content was increased from the zero to the high level.

In this case the high level that they refer to is 10% ethanol. So in formal testing where other variables that could effect fuel mileage are controlled E10 increases fuel consumption by 1.4%. Putting that a different way, if a vehicle gets 30 miles per gallon on straight gasoline, the same vehicle should get about 29.6 miles per gallon on E10 if all other variables other than fuel selection are eliminated.

Source : Effects of Ethanol and Volatility Parameters on Exhaust Emissions

Kohler Fuel Recommendations

Kohler is a company with many business interests. Although perhaps more well known for making bathroom fixtures, they also make small engines that can be found on numerous brands of lawn care equipment and some commercial equipment applications.

In the frequently asked questions section of their website they say that use of E10 is acceptable.

What fuel is recommended for my engine?

Unleaded regular gasoline with a pump sticker octane rating of 87 or higher can be used. If you are required to use oxygenated fuel, blends containing a maximum of 10% ethanol or 15% MTBE are acceptable. Fuels with higher concentrations and methanol blends are not recommended.

Source : Kohler

Honda Power Equipment's Fuel Recommendations

Besides making cars Honda also makes small engines for use lawn mowers, generators, snow blowers etc. And just like their cars Honda small engines have a good reputation for reliability.

According to their website ethanol blended fuels are allowed.

What fuel should I use in my Honda engine?

Honda engines are designed and certified to run on regular unleaded gasoline.

Gasoline is allowed, by regulation, to contain a variety of additives. The same regulation limits how much of some additives, such as alcohol, can be included in the fuel and still allow it to be sold as gasoline. If you look in a Honda product owner’s manual, you will see that a maximum of 10% ethanol is allowed in gasoline (other oxygenates are also listed). Honda engines are designed for good performance and efficient operation using gasoline containing from 0 to 10% ethanol.

Source : Honda

Ethanol Phase Separation

The EPA published a report in 1995 that deals with the issue of phase separation in oxygenated fuels. The primary oxygenates discussed in the report are ethanol and MTBE.

Phase separation occurs when the water content reaches the maximum amount that the gasoline blend can dissolve, any additional water will separate from the gasoline. If the only source of water is from moisture in the air, phase separation is unlikely to occur due to the length of time required.

For example, at a constant temperature of 100 degrees F and relative humidity of 100%, it would take well over 200 days to saturate one gallon of gasoline in an open gasoline can (assuming the only source of water is water vapor from the air). Water absorption from the air is far slower at lower temperatures and humidities. (At a temperature of 70 degrees and relative humidity of 70%, it would take over two years to saturate one gallon of conventional gasoline in the same gasoline can.) Again, oxygenated gasolines can hold more water than conventional gasoline, and would therefore take much longer to saturate with water.

Source : Water Phase Separation in Oxygenated Gasoline

Mercury Marine's Fuel Recommendations

Mercury Marine is a leading manufacturer of outboard engines and stern drives for boats. They maintain a section devoted to ethanol blended fuels on their website.

Some of the issues that I have seen discussed in the media latley with regards to ethanol's use in boats are addressed.

Are Mercury engines compatible with ethanol fuels?

The fuel-system components of Mercury engines will withstand up to 10 percent ethanol in gasoline - the maximum level currently allowed by the EPA in the U.S.

How does ethanol affect my fiberglass fuel tank?

Fiberglass tanks manufactured prior to 1991 may not be compatible with gasoline containing ethanol. It has been reported that, in the presence of ethanol, some resins may be drawn out of fiberglass and carried into the engine where severe damage could occur. If an older fiberglass tank is used, check with the manufacturer to determine if gasoline with ethanol can be safely used.

Are older fuel lines prone to failure? What about gaskets?

During the 1980s, many rubber components for use in fuel systems were developed to withstand exposure to fuels containing ethanol. If rubber components in a fuel system are suspected to be of this vintage or older it may be advisable to replace them with newer ethanol-safe components before using fuels containing ethanol. Check with the manufacturer for advice or frequently inspect these fuel-system components for signs of swelling or deterioration and replace if problems are noted.

Source : Mercury Marine

Evinrude Outboard's Fuel Recommendations

Evinrude is a leading maker of outboard motors for boats. In the Frequently Asked Questions section of their website they state that fuels containing up to 10% ethanol are allowable.

Q - I live in an area where they only sell oxygenated fuels. Will this hurt my motor?

A - Oxygenated fuels should not hurt motors. Motors can tolerate up to 10% alcohol in fuels, which is the maximum allowed by law in the United States.

Source : Evinrude

Briggs & Straton Fuel Recommendations

Briggs & Straton is one of the largest makers of small engines. Their engines can be found on power equipment such as lawn mowers, pressure washer, snow blowers, etc. According to their website E10 unleaded is allowed in all four stroke and two stroke engines.

All 4 stroke cycle spark ignited engines

• Gasoline with up to 10% ethanol (gasohol) or up to 15% MTBE (methyl tertiary butyl ether), is acceptable.

All 2 stroke cycle spark ignited engines

• Gasoline with up to 10% ethanol (gasohol) or up to 15% MTBE (methyl tertiary butyl ether), is acceptable.

Source : Briggs & Straton

Manufacturers Statements Regarding The Use Of Ethanol Blended Fuels

This is an ongoing effort to catalog the various manufacturers statements regarding the use of ethanol blended fuels.

Small Engines

• Briggs & Straton


• Echo Outdoor Power Equipment


• Honda Power Equipment


• Kohler


• RedMax


• Stihl

Marine Engine Manufacturers

• Evinrude


• Mercury Marine


• Yamaha Outboards