Testing for ethanol

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985.

How do you test for ethanol in auto gas?

Recently, I’ve received a lot of e-mails from people who want to know exactly how much the water phase volume will change in the test, and whether they can mix water with the bulk fuel and remove the ethanol to make the auto gas safe for their aircraft.

The field test for alcohol in fuels is meant to be a go/no go or pass/fail type test. It is not to be used as an accurate measure of the amount or type of alcohol in a fuel sample.

The problem is that alcohols will react differently under varying conditions. Alcohols are polar solvents. This means they will absorb water and, when saturated, the water alcohol phase can separate out and drop to the bottom. Now the amount of water the alcohol will absorb and whether it will drop out is dependent on temperature, humidity, and the composition of the fuel and alcohol. Another factor is the amount of alcohol present in the fuel. Most stations post that the fuel can contain up to 10% ethanol. That does not mean it has exactly 10%.

In addition, if you are testing fuel that is not labeled as ethanol-containing fuel, it could be contaminated by some ethanol fuel and have who knows what percentage of alcohol.

The bottom line is that when you are running this test using an Alcohol Fuel Test Kit, you must accurately mark the exact level of the water before adding the fuel. Then add the fuel and mix well. Now look at the water level: If it is higher OR lower than at the start of the test, the fuel fails.

As to using a water wash to remove the ethanol, just say no. Since you do not know how much ethanol is in the fuel to start, it is impossible to know when you have removed it all.

The other real problem is what you would do with the water-alcohol mixture after the “wash” cycle. It will not burn and it would be illegal to put in the wastewater system. The best answer is to work with others (you can find them on our website and at Pure-Gas.org) to obtain an ethanol-free supply of auto gas.

I also received a nice note from Doug Millard, who does a lot of refueling out in the bush. When refueling from five-gallon cans, he always uses a chamois skin inside his Mr. Funnel water separating funnel. He also uses the same set-up to filter the fuel coming out of his tank, even though there is a filter on the tank. This extra safety measure helps protect him from small bits of rubber that can come out of the inside of the hose, as well as bugs and other debris that can get into the hose when not in use. He also keeps a cap on the end of his funnel for the same reason.

This reminded me that on all aviation fuel dispensing nozzles, there is supposed to be a screen in the nozzle to catch any break-up from the hose. When I did airport inspections I used to have the FBO personnel check that screen. It was surprising the number of people who did not know about that screen or had never checked it before. I also found a number of the screens had been removed, probably because they kept plugging up. You may want to ask your FBO about the screen in the nozzle where you refuel.

You can contact Ben at Visser@GeneralAviationNews.com


  1. Arnie Allison says

    Correction to my last comment. DO NOT use leaded fuel in a car or truck with a catalytic converter. The lead will kill it and cost you a lot of $$.


  2. Arnie Allison says

    I did a test on older trucks (pre presure cap tanks) when they would not run in the spring after sitting out all winter. I drained out a gallon into a flat pan – what an ugly mess. After picking up my tools I looked at the sample and it was perfectly clear with blobs of water on the bottom. The alcohol had evaporated and dropped out the water.

    The lesson is that if you operate an aircraft that has alcohol in the fuel and has sat long enough to pick up water which is absorbed by the alcohol you have a serious condition. You drain the sumps and may or may not find water. But when you fly the aircraft and fresh air replaces the burned fuel alcohol can evaporate into the new fresh air liberating WATER which can stop your engine!!

    The answer, check for alcohol in your aircraft fuel tanks. If found drain the fuel and use it in you car or truck with a presure cap fuel system. The trucks that would not run were driven with a large addition of isopropal alcohol until all the water made it through their engines.

    Arnie Allison


    I have been fueling and flying quite awhile and this was all news to me.
    I wonder why it has never become common knowledge, or did I miss it?
    With all the changes is fueling and supplies I would like more info on fuel quality.
    There may come a time when pilots will have to do their own quaility control in the field.
    Knowing what to expect and what is required could save a plane or life.

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