Almost every month I receive a question or two about auto gas with ethanol. The questions usually center on whether it can be used in aircraft and if not, why not.
The answer I give is almost always: “ No because of technical and/or legal reasons.”
There is a fairly long list of technical reasons. Ethanol is an aggressive solvent and will attack rubber-type fuel system components, such as fuel bladders, fuel lines, composite floats and rubber-tipped needle valves, etc. This can lead to fuel starvation, flooding and leaks.
Ethanol is a polar solvent that attracts water. This greatly increases corrosion in fuel systems and shortens the storage life of the fuel.
I have also heard reports of vapor and separation problems at altitude.
So technically, there are definitely problems associated with its use.
In the LSA market, it is a bit of a gray area. Most LSA engines are designed for auto gas and the engine manufacturers’ “technical reps” that I talked to said that their engines would operate on auto gas with ethanol.
However, you will still have the altitude, corrosion, and short storage life to contend with, so I would not recommend it.
As a follow-up, one person asked that since newer cars are now made to operate on fuels with ethanol, are new aircraft? As far as I can tell, most bladders, fuel lines and other fuel system components in new aircraft are ethanol safe. However, because of the other problems, it is still not legal to use ethanol fuels in them.
Several people have asked about using fuel with ethanol in their two-cycle ultralight engines. Here we have another serious problem and that is the leaning out of the air/fuel ratio. Most two-cycle engines run just rich of peak for maximum power. Ethanol is an oxygenated fuel, so it will always lean out the mixture. If you lean out the mixture in a two-cycle, you can easily be operating at peak temperatures in the engine, which can lead to scuffed pistons and other problems.
Several people have asked what to do if they think they may have gotten fuel with ethanol in their aircraft.
The first step is to test the fuel in the tank with a water test.
For the test, make a permanent line about 2 inches from the bottom of a test tube or bottle that’s 6 or 7 inches long. Fill with water to this line, then fill the tube to the top with the fuel. Cover the tube, agitate it, and let it stand.
The ethanol and water will mix and separate out together. If the water level appears to have increased, the fuel contains ethanol and should not be used. Ethanol percentages of less than 5% can sometimes give a reading below the line. Any deviation in the water line indicates the presence of ethanol and should serve as a basis for rejecting the fuel.
If it does have a significant amount of ethanol, the safest step is to drain the tanks and refill with a known “good” fuel.
This is especially critical for low-usage aircraft that will be sitting in the hangar for a while.
If you have a light-sport aircraft that could be OK on fuel with ethanol, you could fly it out and refuel with good fuel. Make sure you get almost all of the ethanol out before putting the plane away for the winter.
The best thing is to drain the fuel so that you get all of it out and then refuel.
Finally, how do you guard against getting ethanol fuel? This is getting harder to do. The best thing is to buy at airports that market auto gas or unleaded 94 octane fuel.
If you are buying your auto gas off site, you will need to test every batch, even if it is marked no ethanol.
An example of a problem is blend pumps that use just one dispensing hose for all grades. Here you could be buying ethanol-free fuel, but if the customer before you was buying fuel with ethanol, there could be a significant amount of ethanol in the hoses and pump.
Whenever I buy fuel for my lawnmower, I always fill my car up first to ensure that the system is clear of the ethanol fuel.
I have also been asked “if there are so many problems with ethanol containing fuels, why do the oil companies still market it?” That is a very good question that I will try to answer in a future column.