Ethanol is a renewable, domestically produced biofuel that is commonly added to the nation’s gasoline supply in varying ratios. Photo: Getty Images


Ethanol is a renewable, domestically produced biofuel made from corn and other agricultural products. The presence of ethanol in our nation’s fuel supply is driven by two primary factors: the Renewable Fuel Standard (legislation from Congress that mandates the use of biofuels such as ethanol and biodiesel) and the octane requirements of the different grades of gasoline in use.

While ethanol has been used as a fuel for about as long as cars have been around, current widespread ethanol use accelerated in the mid-2000s as an alternative to MTBE (methyl tertiary butyl ether) to oxygenate fuel. With this decision to start adding ethanol to the nation’s gasoline supply, the United States became the world’s largest producer of ethanol fuel in 2005.

By 2011, most cars on U.S. roads were engineered to be able to run on blends of up to 10% ethanol (E-10), and manufacturers had begun producing “flex fuel” vehicles designed to use 85% ethanol (E-85). Since 2010, blends of up to 15% ethanol (E-15) have been sold for use in cars and trucks with a model-­year of 2007 or later. However, many auto manufacturers have stated their warranties would not cover E-15-­related damage, so it’s best to check before using this higher blend.

Given how prominent and widespread ethanol is in our gasoline, it’s a good idea to stay on top of the latest recommendations for using, dispensing, and storing ethanol fuel. What are its effects on engines and storage and fueling sites? There are several key areas to examine.

At a glance

Fleets using and storing ethanol-blend gasoline should be aware that:

  • The higher the ethanol content, the lower the energy content
  • Keeping large fuel tanks full can prevent water condensation
  • Ethanol may corrode soft metals in small and off-road engines
  • Fuel distribution systems providing ethanol-mixed fuel may contaminate diesel storage stations.

Can Ethanol-Blend Fuel Damage Engines?

Fleet managers should be aware of four challenges concerning ethanol-blended gasoline: lower fuel efficiency, the possibility of phase separation, lean fuel mixtures, and corrosion.

Ethanol has lower energy content than gasoline, which impacts vehicle fuel economy along with potential changes to the air/fuel ratios used by the engine. Ethanol has about 25% less energy when compared to gasoline, so the higher the concentration of ethanol in the fuel, the greater the loss of economy. A flex-fuel vehicle using E-85 may expect to get about 20-25% less mileage than one using non-­ethanol fuel.

Beyond that, ethanol is hygroscopic, meaning that it draws the moisture from the air into the fuel. E-10 gasoline can hold approximately two teaspoons of water in suspension per gallon before starting to go through the disastrous process of phase separation. Phase ­separation occurs when the fuel can no longer hold any additional water in suspension. At this point, the ethanol and the water will combine together and fall to the bottom of the fuel tank (because ethanol plus water is heavier than gasoline). When this happens, the fuel is ruined because much of the fuel’s octane value is now on the bottom of the fuel tank.

One of the reasons ethanol is used on a widespread basis is because, with an octane value of 119, ethanol is used to round out the octane value of the base gasoline. Companies can start with a lower-octane gasoline base and make up the difference by adding ethanol at the end of the process. If the ethanol phase separates, it carries with it an essential portion of the fuel’s octane value, and this can make the fuel unusable.

The possibility of phase separation of your stored ethanol gasoline can be a huge concern. Once ethanol-­blended gasoline absorbs water, the fuel life is approximately 90 days. No products on the market today can cost-­effectively reverse phase separation after it occurs. And there also exists the possibility of engine damage should phase-­separated fuel be in your fuel tank. The fuel pickup pipes are located at the bottom of fuel tanks, so if the water-ethanol layer is ingested into the fuel system, equipment damage or a breakdown can occur.

Speaking of engine damage, a lot has been written about ethanol fuels causing lean fuel mixtures, which are hot and damaging to engine components. “Lean” describes a condition where there is too much air relative to the amount of fuel in the fuel mixture being supplied to the engine. Fuel injection systems are designed to account for the energy level of gasoline, so anything that takes the place of gasoline, such as ethanol, can cause a hot, lean condition where not enough fuel (relative to the amount of air) is being supplied to the engine.

In today’s modern vehicles, the mission of the vehicle computer is to maintain a 14.7 to 1 stoichiometric air-to-­fuel ratio in what’s being supplied to the engine by the fuel injectors. This is the ideal air-to-fuel ratio for the operation of the catalytic converter, and the computer maintains this ratio by adjusting how long the fuel injectors stay on.

Problems arise when conditions develop that keep the engine from reaching or maintaining this ideal ratio. Sometimes it’s a mechanical fault, such as if your engine develops a vacuum leak, causing a lean condition. The computer would compensate for this by richening the air-to-fuel ratio (adding more fuel than it’s supposed to) which cools things down, but also reduces your fuel economy.

Modern computer-controlled fuel-­injected engines have an additional advantage in that they have the ability to compensate for lower energy fuel. A flex-fuel vehicle can detect the higher levels of ethanol in your fuel and appropriately adjust the injector timing and other factors to make sure your engine runs properly. If you don’t have a flex-fuel vehicle and your gasoline happens to have ethanol content higher than 10-15% (which happens more often than you think), the computer isn’t able to detect this difference, and it keeps running the engine under the assumption that there’s less ethanol in the fuel than there really is. This is when you can see performance problems and issues with the proper air-to-fuel mixture supplied to the engine.

Phase separation, as shown in this photo, occurs when water mixes with ethanol-blended gasoline. Photo courtesy of James Dunst


Ethanol's Effect on Small Engines

Carbureted vehicles, all-terrain vehicles, motorcycles, and small gasoline-­fired engines commonly found in lawn equipment also do not have the ability to adjust the air-to-fuel ratio. They have a fixed jet that meters fuel into the engine and is calibrated for the proper energy level of gasoline. If lower energy ethanol-blended fuel passes through the jet, you can end up with a lean, engine-­damaging mixture, with no way to correct it.

Beyond the energy level problems of the fuel, these small engines can also suffer from ethanol’s lubrication problems. Two-cycle engines that get internal lubrication from oil that is added to the gasoline can have real problems if the ethanol concentration is too high. Ethanol’s water attraction can interfere with this normal internal lubrication process, causing, in some cases, damage or the destruction of the engine.

Small engine and off-road engine systems, as well as fuel distribution systems prior to the filling station, can also be affected by corrosion. Ethanol is highly corrosive, and research on fueling components has shown that unprotected products made of exposed, soft metals may show degradation over time when in contact with ethanol. Damage to metals such as zinc, brass, lead, and aluminum can occur and unfortunately, a number of fuel system components are made with these metals. In addition, damage to other materials such as natural rubber, gasket materials, and plastics can also occur. As these materials degrade, the dissolved materials may contaminate fuel. Fortunately, these kinds of fuel system problems aren’t typically seen in on-road vehicles.

Ethanol can corrode some metals, such as the corrosion shown on this carburetor from the back-up pump of a utility. Photo courtesy of James Dunst


Fuel Storage & Dispensing Solutions

Given the potentially serious problems ethanol-blended gasoline can cause in your equipment, it’s important to follow best-practice storage and dispensing guidelines to minimize the chance of these issues.

Fuel storage containers should be kept in a cool, dry place to limit temperature changes that affect fuel life. If you cannot drain fuel from equipment fuel tanks, it is best to keep them full to reduce the air space over the fuel. This is extremely important, in particular, with boats working in a high moisture environment. In contrast, modern cars and trucks have sealed fuel systems with air and humidity being vented out the fill pipe when fueling, which reduces the chances of absorbing water into the fuel.

For fuel storage, most large gasoline storage tanks are vented to the atmosphere, exposing them to water contamination. It only takes a seven-degree change in air temperature for condensation to form on tank walls. Keeping these tanks full will reduce water buildup in the fuel by eliminating both available air space and tank wall surface space for condensation to accumulate.

On the fuel dispensing side, fueling stations have been adversely affected by ethanol fuel’s contribution to microbially induced corrosion (MIC). This is especially true of diesel storage stations, which invariably see low levels of ethanol contamination from the fuel distribution systems providing the fuel. Vapor space corrosion with associated corrosive damage may be found in a majority of diesel storage systems themselves, which makes maintaining both gasoline and diesel storage tanks and distribution equipment a challenge. All metal piping and tank components that are exposed to ethanol or ethanol vapors should be coated with amine-based corrosion inhibitors made to protect against corrosion. Tanks should also be double-­walled and preferably constructed from stainless or cold-­finished steel. Fiberglass can also be used if the resin is compatible with ethanol, but keep in mind that any metal components (such as in leak detection and release prevention equipment) are still susceptible to MIC-related damage.

As for small engine problems, much of this equipment is seasonal, which means storing the equipment with ethanol-­blended gasoline in the fuel tanks and carburetor can be problematic. It is best to use corrosion-­inhibiting additives, or if possible, drain the fuel completely from the fuel tank and carburetor. If the equipment has a fuel shut-off valve, turn off the fuel while the engine is running in order to burn the fuel remaining in the carburetor before you put it up for storage. Ethanol-­blended fuel left in the fuel system for long periods of time can cause severe corrosion, requiring replacement of the damaged components.

Editor's note: James Dunst is the national training director for Bell Performance and is a specialist in fuel-related problems and solutions. He is a member of the Florida Association of Governmental Fleet Administrators (FLAGFA).

Originally posted on Government Fleet