If gasoline with 10% ethanol is stored for a few weeks, will the ethanol evaporate?

I have read that to check for ethanol in gas is to add a little water to a container; mark the level and add gas. If the water lever stays the same, it is ethanol-free. I purchased ethanol free-gas and it passed the test. I then tested some gas with 10% ethanol that had been stored for approximately 1 month in a plastic gas can and got the same results. According to my source, the water/ethanol level should have gone up.


Whether or not the ethanol will evaporate depends on your container. If the container isn't air-tight then both your gas and the ethanol will leak into the atmosphere.

With regards to the 'level test'. Generally, ethanol mixes well with both water and organic solvents. If this is the case with fuel (and I suspect it is - it is mainly hydrocarbons), you will not see appreciable changes in the level of the 'water'.

However, for this type of qualitative test, you should keep a few things in mind. Depending on the diameter of the container you used and the amounts of water and fuel, you will get varying amounts of level change, if any. You could try a very thin tube and mix the components well. After mixing leave the phases to separate for a good while before checking your level.

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