Testing E85

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Bill Martin
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Testing E85

Post by Bill Martin » Fri Jan 10, 2020 11:04 am

Ran content tests on my early 2019 jugs to see if I wanted to use or discard. Used the Holley calibrated E85 test tube and all my results came out about 90%. Of course I was expecting 85%.

Is this test considered accurate? Is there a generally agreed upon shelf life on pump E85, properly stored away from UV and temp extremes?

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Marshall Grice
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Re: Testing E85

Post by Marshall Grice » Fri Jan 10, 2020 12:07 pm

I haven't really had any problems with the E85 in socal. the main problem with old e85 is it absorbs water from the air, but the good news is you live in a desert.

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Bill Martin
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Re: Testing E85

Post by Bill Martin » Fri Jan 10, 2020 1:45 pm

Thanks Marshall. Since the content test is water-absorption based, then I would think significant water contamination should show up in the test results. I assume driving the "clear space" at the top down. Which I'm not seeing. But I still can't explain why mine seems to test at E90. Most people complain about too low an alcohol content. Which is why I wonder about the accuracy of this test.

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Anthony P.
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Re: Testing E85

Post by Anthony P. » Fri Jan 10, 2020 3:58 pm

Bill Martin wrote:
Fri Jan 10, 2020 1:45 pm
Thanks Marshall. Since the content test is water-absorption based, then I would think significant water contamination should show up in the test results. I assume driving the "clear space" at the top down. Which I'm not seeing. But I still can't explain why mine seems to test at E90. Most people complain about too low an alcohol content. Which is why I wonder about the accuracy of this test.
When I had my flex fuel sensor in the miata E90 from the pump wasn't uncommon. I think I saw a low of E80, but I didnt ever see a "winter" version.

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Marshall Grice
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Re: Testing E85

Post by Marshall Grice » Sun Jan 12, 2020 6:09 am

E90 is common.

Julian Manolov
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Re: Testing E85

Post by Julian Manolov » Mon Jan 13, 2020 10:24 am

Beware with the Flex fuel sensors, because (just like the O2 sensors don't really measure air/fuel ratio) these don't really measure ethanol content!!
Inside the sensor it is pretty much two electrodes dipped into the fuel (which form a capacitor) and it measures the capacitance.
It has a preset for what's the capacitance of pure gasoline and ethanol and interpolates between the two. The reason it also has a temperature sensor inside, is because the capacitance changes with temperature of the fluid so it has to correct the readings for it.
Any other fluid added to the mix (like absorbed water) will instantly screw up the measurement and makes your reading meaningless.
Absorbed water will raise the number your Flex sensor shows and if you dip it in just water, it will show the water as 100% Ethanol! :D
Last edited by Julian Manolov on Mon Jan 13, 2020 12:54 pm, edited 1 time in total.

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Marshall Grice
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Re: Testing E85

Post by Marshall Grice » Mon Jan 13, 2020 12:38 pm

well as long as there isn't so much water that phase separation occurs (like exactly what happens when you test E85 by adding water) then it's safe to run. I think E85 can hold something like 4% water without phase separation, which is likely a big source of error in the phase separation testing of e85. But again, you can look at your jug of E85 and know immediately if it's bad or not because it will look like the water/ethanol mix that happens after you test it.

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Re: Testing E85

Post by Julian Manolov » Mon Jan 13, 2020 12:47 pm

Someone being amazed by Flex sensor readings. Just ignore his nonsense ramblings about the sensor measuring gasoline content
:lol: at him being surprised by the water thing
https://www.youtube.com/watch?v=8DZhLjwsWVY

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Marshall Grice
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Re: Testing E85

Post by Marshall Grice » Tue Jan 14, 2020 4:19 am

Bill Martin wrote:
Fri Jan 10, 2020 1:45 pm
Thanks Marshall. Since the content test is water-absorption based, then I would think significant water contamination should show up in the test results. I assume driving the "clear space" at the top down. Which I'm not seeing.
Seems like you have it backwards. When you do the water test the water mixes with ethanol and sinks to the bottom. The clear stuff on top is the gas. So with extra water in the fuel it will measure as higher ethanol content.

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