Here's a file that shows you how to do the E85 % test.....and the formula you need to use to crunch the numbers.
Something I found is that you don't need to SHAKE the mix really hard. Water bonds with ethanol MUCH better than with ULP, so just a really light tipping back and forth for a moment is enough to mix the water & E85. If you shake it really hard, it will take much longer for the mix to settle down for an accurate reading.
Mixing water and ethanol is also an exothermic reaction.....the measuring cylinder gets warmer when you add the water.....bit of useless info for ya!
You may also hear a lot of hype about "phase separation" where your E85 will absorb so much water from the atmosphere that the ULP separates out of the fuel solution....as seen in the test above. The bad thing with this is that there is potential for your engine to get a big gulp of 91/98ULP and no ethanol....which will cause some serious detonation of that ever happened. BUT from my tests, you need so much water in the E85 for this to happen, that I just can't imaging it ever happening unless you accidently filled up with a fire hydrant ;)
Here's a pic with just enough water added to show the pinky globules of ULP forming on the top of the water (looking from underneath in a 2L bottle). Can't recall the exact numbers, but for a full fuel tank, you'd need to add a gallon or 2 of water.
