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Ethanol And The Growing Issue Of Small Engine Problems

Ethanol And The Growing Issue Of Small Engine Problems

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Paul Brown

Those gas-powered yard tools in your garage are a big investment. Proper care and maintenance are key factors in keeping them running. And yet, so many well-intentioned homeowners make the mistake of heading to the gas pumps when it’s time to refuel. This could be causing major damage to the small engines in your garage if you aren’t reading the fine print.

Does Ethanol damage small engines? Ethanol damages the integrity of plastic and rubber in small engines resulting in parts failing, higher running temperatures, and poor reliability. Other known issues include phase separation, vapor lock, corrosion, oxidation, and altering of the combustion and compression ratios.

What Is Ethanol?

Ethanol is a biofuel, an alcohol-based formula derived from sugar. Common sources used to create ethanol include corn and sugar cane. It is essentially a chemical compound made up of methylene and hydroxyl. The Ethanol molecule is a volatile, flammable compound similar to gasoline.

Conceptually, this biofuel, when mixed with traditional gasoline, reduces the use of crude oil (source). In addition, it supports the agricultural industry with almost $100 million of federally-funded incentives being committed through the Biofuel Infrastructure Partnership.

It is a simple chemical compound made up of methylene and hydroxyl. The Ethanol molecule is a volatile, flammable compound similar to gasoline and is utilized in several industries including internal combustion engines.

The Rise Of Ethanol In American Fuels

The Energy Policy Act of 1992 radically changed the landscape of alternative fuels and America’s dependence on foreign oil. State and local governments were compelled to implement initiatives to reach alternative fuel levels set by the federal government. The Act describes biofuels as methanol, ethanol, and other alcohol blends. Congress expanded the Policy in 2007, to include 36 billion gallons of ethanol mixed to unleaded gasoline.

Don’t underestimate the influence of politics on the expansion of Ethanol usage. The Renewable Fuels Association invested over $1 million in lobbying efforts in 2018 and biofuels trade group Growth Energy put forth $1.37 million as well, urging the now successful year-round sale of E15 among other goals (source).

The idea of replacing traditional fossil fuels with a plant-based fuel source is enticing but alas, challenging.

  • According to the International Energy Agency, the world is not close to providing enough biofuel to power modern internal combustion engines. The output would need to triple by 2030 to provide workable progress (source).
  •  Corn and soy-based land production take away from food production. David Pimental of Cornell University concluded; producing biofuels and conversion to a workable fuel is not worth the energy (source).

In fact, since 2005, the percent of corn grown that is used for ethanol production has increased from 12.4% to 38.5% in 2019, meaning over a third of America’s corn supply is now dedicated to production of this biofuel.

Ethanol not only damages small engines, it requires over a third of America's corn supply to produce.
Source: USDA Economic Research Service

The Promise Of Biofuels

Most of the gasoline sold in the United States contains at least some ethanol and promises several environmental and economic advantages.

  1. It is a renewable resource, meaning indefinite supplies.
  2. It is a domestic resource for most countries. This advantage provides independence from the whims of oil-producing countries.
  3. it produces no net carbon dioxide.

The ethanol molecule is oxygenated, which helps the fuel to burn cooler. Oxygen inside the molecule combines with oxygen in the air to provide a complete burn process.

Conceptual Benefits:

  • Cooler burns offer better spark plug life and fewer deposits from combustion.
  • Additional oxygen in the ethanol molecule helps gasoline to burn completely as well.
  • Better combustion offers up to a 25% reduction in greenhouse gases and other toxic exhaust fumes.

What Are E10, E15, and E85?

You may have seen fuel designations such as E10 or E15 at your local gas station. But what do these designations mean?

  • E10 – approximately 10% ethanol by volume has been added to unleaded gasoline. This blend will often be designated with a label “may contain up to 10% Ethanol”.
  •  E15 – 15% ethanol with 85% unleaded gasoline. It is promoted as a safe and efficient fuel for most modern automobile engines (source).
  • E85 or FlexFuel – This mixture is 85% ethanol and only 15% gasoline. Only designated flexible fuel vehicles can use this higher mixture of ethanol. As of 2017, 21 million of these FlexFuel-certified vehicles were operating in the United States.

It is important to note, any internal combustion engine built before 1986 is not compatible with ethanol-blended gasoline. The EPA has approved the use of gasoline with as much as 15% ethanol in vehicles 2001 and newer.

How Ethanol Effects Small Engines

On the surface, the infusion of ethanol into our fuels is an environmentally-minded initiative that supports US farmers. From that perspective, the use of biofuels makes sense. And, in the case of modern automobiles, this mixing works just fine.

But when it comes to gasoline-powered outdoor tools and equipment, ethanol can wreak havoc on the small engines powering them.

Extensive time and effort have been committed by small engine manufacturers to study the relationship of ethanol on the performance of their engines. These same manufacturers have developed specific fuels, kits, and recommendations for use in their equipment.

Ethanol Changes The Combustion And Compression Ratio In Engines

Because of its higher octane rating, ethanol alters critical timings within an engine including spark timing, compression ratio, and the air-fuel ratio. Modern automobiles can adjust for these variances thanks to computerized fuel injection capabilities. Unfortunately, small engines like those on outdoor power tools lack the technology to make these adjustments (source).

These timing systems and ratios are designed to keep your small engine running efficiently. Alternations can result in premature degradation, higher running temperatures, and part failures. For example, the air-fuel ratio ensures the appropriate amount of oxygen to properly and efficiently burn fuel (source). When this ratio is altered, fuel burns less efficiently resulting in poor engine performance.

The high octane rating of ethanol is touted as a key benefit by the US Department of Energy, even explaining that race cars in Indy 500 races often use fuels with high octane (source). But your lawnmower is not a race care.

It’s important to understand that variations from manufactured specifications have a compounding effect not only on the performance of small engines but on their reliability.

Ethanol Bonds With Water And Separates From The Fuel

Two-stroke oil bonds to gasoline providing adequate lubrication. The oil will not bond to ethanol, leading to poor lubrication. Using ethanol blends is especially dangerous for residential use when the equipment can sit for days and even months.

Ethanol continues to collect water the longer it remains in the tank and Phase Separation occurs, meaning two distinct layers form, a gasoline only layer and ethanol/water layer (source).

Ethanol Is A Solvent And Drying Agent

Ethanol-blended gasoline can dissolve varnish and old gum deposits from storage tanks. These deposits can pass through and clog the internal workings of small spark engines. Both ECHO and HONDA agree: these pass-through deposits can have damaging effects on carburetor jets, intake tracts, valves, and valve guides.

Vapor Lock

Vapor lock is the process of liquid gasoline turning to a gaseous state while still in a fuel delivery system. Vapor lock prevents the fuel from moving freely through fuel lines and into the carburetor or fuel injectors.

The U.S. periodically tests fuels for a vapor-liquid ratio temperature (source). This ratio indicates the tendency of fuels to vaporize in internal combustion engines. Vapor lock is a much bigger problem in automotive engines; however, small spark engines can develop vapor lock. Vapor lock occurs at lower temperatures when ethanol has been added. This condition can cause severe performance problems.


Corrosion is another significant problem associated with ethanol-blended gasoline. Ethanol attracts water. The chemical mix of water and gasoline accelerates the corrosion process of metal parts in the engine. Look for these signs of advanced corrosion:

  • Irregular RPMs, meaning air to fuel ratio is off-balance.
  • The engine will not start or turn over.


Gasoline and ethanol can oxidize similar to the process of iron rusting. Adding ethanol to fuel changes the chemical properties of gasoline. Fuel oxidation creates water, peroxides, and acids causing corrosion of any metal parts in a small spark engine. Instead of rust flakes entering the fuel system you will get gum and varnish.

There are also issues with increased running temperatures. Below is a television new stations’ investigative report into ethanol and it impacts on small engines where they cover, among other issues, higher running temperatures.

Good Question: Can Ethanol Damage Small Engines?

Legislative Changes Increase Risk Of Damage From E15 Fuels

Until 2019, the US government held what has come to be known as a “summertime ban” on E15. This seasonal restriction was aimed at reducing smog but it had an unintentional benefit for owners of gas-powered outdoor power equipment. Because the summer months are when the use of outdoor equipment and tools are at their highest, the ban helped to prevent us from absent-mindedly filling our tanks with too high of a concentration of ethanol mix.

In May of 2019, however, the Environmental Protection Agency finalized efforts to comply with a White House mandate that removes the summertime restriction on sales of E15 (source). As a result, it is more important than ever to carefully read the ethanol content disclaimer at the fuel pump before filling the tank on outdoor power tools.

Manufacturer Recommendations Regarding Ethanol

Husqvarna considers the use of ethanol a bad choice of fuel and recommends ethanol-free gasoline. Husqvarna pre-mixed 2 cycle fuel is ethanol-free and high in octane.

Briggs & Stratton, the largest manufacturer of small engines in the world, also consider the use of ethanol in their engines a bad choice. If you use an ethanol mix of E15 or higher it will void your warranty. (source).

Many biofuel and ethanol proponents point to Briggs & Stratton’s fuel recommendation statement. “Gasoline up to 10 percent ethanol (E10, gasohol) or up to 15 percent MTBE is acceptable.” Nowhere in the statement does it say ethanol-blended gasoline is “recommended.”

Briggs & Stratton recommends TruFuel 4-cycle Ethanol Free Fuel available from several retailers including Amazon, ASIN-B009QT1KLO. This ethanol-free fuel leads to a cleaner burn through the engine combustion cycle. TruFuel for 2 cycle engines adds the correct mix of synthetic oil to quality gasoline for outstanding engine performance. TruFuel provides better trigger response and extends the life of gas-powered equipment.

Note: These different brands of ethanol-free fuel are more similar than you may think. To learn more, read our comparison of premixed fuels.

Choosing The Correct Fuel For Your Outdoor Yard Equipment

Look for ethanol percent notices at fuel pumps.

Make sure your lawnmower, snow blower, or generator stays running efficiently for years by choosing the right gasoline. First and foremost, always consult the owner’s manual. The manufacturer is the ultimate Subject Matter Expert for your gas-powered yard tools.

Even the best gasoline can begin to deteriorate in a tank after 30 days. Always drain the tank if not in use and when you store gasoline in a yard tool tank, use a fuel stabilizer like Briggs & Stratton Fuel Treatment. The treatment bonds with the gasoline to prevent evaporation.  

Most manufacturers of small spark engines recommend the following when choosing gasoline for your yard tool:

  • Clean, fresh unleaded and a minimum 87 octane. There is no advantage to using a higher octane rated gas. Small engines have low compression ratios; therefore, higher octane provides no added benefit. Higher octane might make your engine harder to start and idle rough.
  • Only E10% or less ethanol by volume is considered safe for small spark engines. However, even this blend is usually listed as “acceptable”, not “recommended”!
  • Higher altitudes of 5000 feet or higher should have a minimum of 85-octane and a high-altitude adjustment kit installed.

Outdoor Power Equipment Institute

Probably one of the biggest advocates for responsible use of Ethanol in small engines is the Outdoor Power Equipment Institute (OPEI) based out of Alexandria, VA. Among the initiatives that this organization is committed to, is the increased awareness of how Ethanol affects small engines and the importance of choosing E10 or less when fueling outdoor power equipment.

Kris Kiser, President & CEO, recommends following the manufacturer guidelines from the owner’s manual to ensure safe fueling practices. He was kind enough to weigh in on this topic and provided a wealth of insight into the growing concerns over ethanol fuels for outdoor power equipment.


Regarding the recent lifting of the E15 summertime ban, Kiser reinforced the importance of consumers paying close attention to the fuel being purchased.

“As the fuels marketplace is evolving” Kiser explains, “you can no longer count on being able to put the same fuel in your mower that you also use in your car or truck. You must pay attention at the pump so you can protect your power equipment. You must put the right fuel in the right engine product”.

OPEI’s current Look Before You Pump campaign reinforces the importance of consumer mindfulness when fueling.


OPEI takes this need for awareness seriously, distributing thousands of educational materials. They also speak out regularly in the media, advocating for consumers to be educated on safe fueling practices for their outdoor power equipment.

Included in their efforts is an urge for improved labeling on gas pumps. “Increasingly, consumers are telling us, through our Harris poll research, that they are making fueling mistakes,” Kiser explains. “Currently, only a small warning label is placed on pumps with E15 to warn consumers to not use this fuel in outdoor power equipment. Ethanol proponents also are marketing E15 as 88 Octane. We find this misleading and only adds to the confusion as to which fuel a consumer should purchase for their outdoor power equipment”.

Kiser reported that their recent Harris Poll research found that more than 1 in 10 equipment owners are mis-fueling their outdoor power equipment. Specifically, he stated that 12% of outdoor power equipment owners admit to using fuel with higher than recommended ethanol (E15/E30/E50/E85) for their outdoor power equipment.

The use of E15 or higher represents an unnecessary risk to gasoline-powered yard tools and outdoor equipment. if you aren’t paying attention, you may be using damaging levels of Ethanol-blended fuel.

Ethanol Education for Equipment Users
Kris Kiser, President & CEO of OPEI, on the importance of paying attention to the fuel purchased for outdoor power equipment.

Steps To Safe Fueling Practices Of Outdoor Power Equipment

The most fundamental practice that you need to employ is to pay attention to the fuel that you are purchasing for your gas-powered yard tools and other outdoor power equipment. Ensure an E10 or less ethanol mix. If you do not see a sticker or notice of the ethanol content, ask before you buy! You can avoid a tremendous amount of issues with your small engines by simply ensuring the proper ratio of gas-to-ethanol in your fuel tanks.

In addition to verifying the Ethanol content when fueling, Kiser advises proper labeling of stored fuel. “We recommend that you label your gas can when you get home with the ethanol content for the fuel and the date of purchase. Gasoline should not be left in your mower, string trimmer, or any other outdoor power equipment product for more than 30 days, or it can phase separate due to the ethanol found in today’s fuels”.

Stay Informed & Spread The Word

As much as we would all like to believe that biofuel companies and legislators have our best interest in mind when making changes, it is our responsibility to ensure that we use the proper fuel for our gas-powered tools and help others to be aware of the issues that high-level ethanol fuel blends pose to small engines. Stay informed.

OPEI promotes awareness through several social media channels. You can follow them on Facebook (, Twitter (@OPEInstitute), or Instagram (@weareopei) and share their #ProtectYourPower posts.

Kiser also advises not overlooking the power of word of mouth. “When you are out in your yard or neighborhood, talk to your friends and neighbors about safe fueling for outdoor power equipment“.

Special thanks to Kris Kiser for his insight and assistance. Visit for more information on OPEI’s awareness campaign.