Ethanol Train Photo by F. John Hay
Ethanol loading facility. Most ethanol facilities have train car loading to ship ethanol by rail to markets in the east and west. (Photo by F. John Hay)

My Favorite Fuel Links

Changes In Gasoline IV: A detailed resource to understand the past and present properties of Spark Ignition Engine Fuel

Ethanol and Gasoline Blends in Small Engines: Oklahoma State University Extension

Ethanol and Small Nonroad Engines: Kansas State University Extension

Ethanol and Water Contamination — Comparing Off-the- Shelf Water Removal Additives

Download complete study

Ethanol will mix with water and thus gasoline ethanol blends can hold some water. This is of particular concern for small engines and engines which are used intermittently due to water contamination during storage. We set out to answer two questions.

  1. How much water can E10, and E15 gasoline ethanol blends hold in solution?
  2. Can off the shelf fuel additives increase the amount of water held in solution?


Water held in gasoline ethanol blends
FUEL Water Held in Solution
E - 0 Zero teaspoons per gallon
E -10 3.06 teaspoons per gallon
E - 15 6.47 teaspoons per gallon
Fuel Additives Claiming to Remove Water
Additive Water Held in Solution
STP No increase in water holding 
BG - Ethanol Fuel System Drier Increased water holding by 0.23 tsp per gallon
Iso-HEET Increased water holding by 0.23 tsp per gallon
Stabil - Ethanol Treatment No increase in water holding
Rislene No increase in water holding
HEET Partial Effect: Solution was more clear but phase separated layer remained. we tested water additions in 0.01% increments
Seafoam No increase in water holding
Valvoline - Nitro Shot No increase in water holding


  • Unlike pure gasoline ethanol blends can hold small amounts of water in solution which is then run through the engine harmlessly. In pure gasoline small amounts may build up in the tank.  
  • Only 2 of 8 fuel additives tested increased the amount of water held in solution.  All claimed on their label to "remove water", "solve phase separation", "dry the fuel" etc

Our Recommendations

  • Use fresh fuel. Use within 30 days of purchase is best. 
  • Store lawn mower and other small engines empty in a dry place (if not empty then store them completely full to minimize air space). Fuel additives for fuel stabilization are recommended by many manufacturers. This study did not test these other properties of the additives.
  • Large amount of water contamination in a fuel tank is likely equally bad for E-0 or an ethanol blend. Avoid water contamination by covering small engines or storing them in a shed or garage.

Changes in Gasoline at the Pump - September 2013

LINCOLN, Neb. – Choices have changed at the gas pump, but drivers shouldn't see a change in how fuel performs in their cars, a University of Nebraska-Lincoln Extension educator says.

Motorists for many years have had a choice of gasoline fuel with octane ratings of 87 regular, 89 with 10 percent ethanol 91 premium. However oil companies have started to run a sub-octane fuel up the pipeline, which is 83 or 84 octane, said John Hay, associate extension educator in biological systems engineering at UNL.

Mixing ethanol with the sub-octane fuel gives it the octane boost it needs to reach 87 octane. Ethanol has an Octane rating of 100. Fuel stations have begun to change their pumps and labels to reflect the new blends. "This sub-octane fuel needs to be blended with other fuel types to make it the 87 octane level or above we need at the pump," Hay said. "So basically, 87 with ethanol replaced the 89 with ethanol, and our low cost option at the pump is now 87 with ethanol."

Hay said for those who's owners manuel calls for minimum 87 and used to fill up with low cost 89 with ethanol, they can now fill up with 87 with ethanol and it will work the same in their engines. 

Before the changes, Hay said there was about a 10-cent price difference in regular gas versus the 10 percent ethanol blend. However, since the changes, that has been ranging 15 to 25 cents across the state.

"The reason is because the 87 regular used to be just the fuel coming out of the pipeline; now it has to be blended with 91 octane premium fuel to make the 87 octane regular" Hay said.

The majority of the U.S. has already seen this change and Hay said Midwest fuel stations will be deciding what blends to carry and what prices to charge over the next few months.

An octane rating ranks fuel's ability to compress without detonating.

"The average car needs a minimum octane rating of 87," Hay said, consult your owner's manual for minimum octane required for your car. "To take advantage of higher octanes, you need a car with higher compressions, such as a high-performance sports car."

Octane is not a rating of energy density and both the 87 with ethanol and the old 89 with ethanol have the similar Btu content and will both give drivers the same gas mileage.

Hay says another fuel fact, is about winter and summer fuel. As winter approaches oil companies will begin their annual change to "winter" fuel. This winter fuel will have the same octane but is made of shorter chains of hydrocarbons and is thus more volatile and less energy dense. The higher volatility helps with cold start in winter conditions yet has less energy than summer blend gasoline. This reduction in Btu content will be accompanied by lower gas mileage but also a lower price at the pump. Hay says the oil market has a lot of price volatility and thus price changes due to switchover like summer to winter and winter to summer are hard to notice. Similarly driving conditions and styles make fuel mileage fluctuate making small changes in the fuels energy hard to distinguish.

F. John Hay
University of Nebraska Extension Educator - Energy