How to test for ethanol in your fuel

[a64pilot]

I keep seeing posts blaming ETH (ethanol) for poor mileage and speculation about whether the fuel in their car has it or not. The easy way to test fuel for ethanol is to place about 10 to 20% of the cylinders capacity of water in a graduated cylinder. (A canning jar or even a peanut butter jar with a mark on it will work.) Fill the remaining jar with gasoline, cap it and shake it. Allow it to settle. If there is alcohol in the fuel it will bind with the water and the level of the water will increase significantly. A pump marked to contain 10% ETH may contain ETH, but not necessarily, it's hit and miss.
I know this because several aircraft are allowed to burn auto gas, but not if it contains ETH, so you learn to check before you buy. The catch is that the next tanker truck load may or may not contain ETH in it, so you have to check every time. ETH does have less BTU's per volume than gasoline so more of it has to be burned to generate the same amount of heat.
It may account for changing FE even though you have eliminated other variables.

[TonyPSchaefer]

Thanks for the post, Pilot.
Though I'm a little confused, I suppose.

When you say, "place about 10 to 20% of the cylinders capacity of water" are you saying, "fill a jar about 10% - 20%"?

So it sounds as though you are saying:

1. Find a glass jar.
2. Place water in it: about 10% - 20% of the jar's capacity.
3. Mark the jar where the water line is.
4. Fill the jar the rest of the way with gasoline.
5. Shake vigorously.
6. Check the amount of water in the jar to see if it is higher than when you started.

Is that about right?

[a64pilot]

You got it tony exactly. I save the fuel in the bottle and carefully pour it off and put it in our aircraft tug. The water left in the bottle I pour off into a pan and allow it to evaporate. It's a mix of ETH and water of course, and lord knows what else, I would not pour it down the drain.