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Old 07-18-2019, 10:53 PM   #8853
Scooby Newbie
Member#: 298502
Join Date: Oct 2011
Chapter/Region: RMIC
2011 WRX sedan


Originally Posted by StiLimited View Post
I have to drive into Vegas to get my E85 so I buy 50-100 gallons at a time and keep it in my shed. When I buy it it tests about 80-85% but after sitting in my shed for 6 months it's now 90%. So for some reason the gasoline is evaporating and the ethanol is staying behind. (best guess) I'm storing the fuel in High-density polyethylene jerry cans. ( I've tested this for 3 years now and it's always the same results. I also use the stabil for ethanol fuel stabilizer if that has any effect I don't know. Next time I'll test before and after mixing.

I like the jugs cause they can stack 3 even 4 high when full. :-)
This got me curious about how FlexFuel sensors actually work. This is what I found...

Typical sensors used for FlexFuel setups determine ethanol concentration by measuring the relative permittivity of what's flowing through the sensor. Gasoline has a lower relative permittivity then ethanol. Water has a higher relative permittivity then ethanol. Keep in mind ethanol is hydrophilic (water loving), so it will absorb water vapor in the air over time.

What's most likely happening in your case; the E85 is slowly absorbing water vapor in the air, which will cause a FlexFuel sensor to read higher concentrations of ethanol then actual. The Stabil may also be throwing off the readings. You could test the later by running E85 through a FlexFuel sensor without Stabil, adding some Stabil to your tank and then seeing what the sensor shows after driving around for a bit to mix it in the fuel. See the below links for more info:
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Last edited by HuckFinn; 07-18-2019 at 11:13 PM.
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