Testing the Percentage of Ethanol in E10 Pump Gas -
     Stored Approximately 14 Months

This is a look at testing the percentage of ethanol remaining in E10 gasoline after it has been stored in plastic bottles for a period of approximately 14 months.  This testing was conducted during August 2012 on gas samples which were previously collected during June of 2011.  The ethanol content of this sample was checked on the day that the gas sample was originally collected, and can be viewed at this link.   The gas tested on this page is one of several samples which have been stored in porous plastic bottles in a garage that ranged in temperature up to approximately 100 deg F and humidity in the high 90% region.  While the accuracy of this test phase separation test method has still not been precisely determined, one can see in relative terms how ethanol content in E10 gasoline may vary over time.

The following test data looks at the ethanol content of E10 gasoline over time.  It can be seen in this separate link, that the ethanol content of E10 gasoline will not separate from the gasoline, unless artificially forced through the addition of water.

Measuring Ethanol Content in Stored E10 Gasoline
The following picture shows two of the several samples of E10 gasoline which I used for this comparison testing.  These particular samples tested at 7.5% ethanol on June 20, 2018.  Of note is the container on the left.  I intentionally left some of the caps on sample bottles loose, and tightened others, to see if room air had any effect on the samples.  The bottle on the left had a tighter cap and appears to have been drawn in, as gases have evaporated out of the bottle.  This is worth noting, related to the results of the ethanol testing below...

Water measured in

Using the same phase separation procedure described on other pages of this discussion, I tested this fuel sample that had been stored for approximately 18 months. Again, first water is added to the "fill line" in the tube.  This provides the additional water volume which will cause phase separation in the fuel sample.

Water measured in

Next the gasoline sample to be tested was added to reach the fuel "fill line" at the top of the tube. I had pre-mixed the blue marker dye in the gas sample before pouring the E10 gasoline into the test vial.

Gas Measured in

The following picture shows a closeup of the measuring scale for the ethanol content, after the test tube had been shaken and allowed to settle out.  While this sample was measured as containing 7.5% of ethanol on June 20, 2011, when tested again at the end of August of 2012 it shows only approximately 3.5% ethanol content.


Dye Added

So, while the liquid ethanol content did not separate over time, a significant amount of ethanol has evaporated out of the mixture.  (Note that the bottle tops on these samples were not tightly fastened, to intentionally allow the E10 to be exposed to room air/moisture.)

The next picture simply wraps things up by showing the tested sample, the bottle it was stored in for over 14 months, and the beaker in which it was initially mixed with marker dye to examine how well the ethanol content had stayed in suspension in the gasoline while sitting in a plastic container in an environmentally uncontrolled space, subject to room air, for an extended period of time.

Ethanol Level

As noted previously, the test kit which I used for these measurements was initially developed for the aviation industry to show the existence and relative percentage of ethanol which may be present in gasoline.  This method of ethanol measurement is not intended to be as precise as that conducted in a laboratory.  However, the measurement is generally accurate within the tolerance of the markings on the tube and is good for showing relative comparisons of ethanol in E10 gas from different sources.  In this case it shows that while E10 gas samples may not physically degrade over time, the ethanol content in these samples fell from 7.5% to approximately 3.5% over a period of 14 months.  Subsequent testing on additional bottles of this sample batch of fuels continues to show the same trends.  The E10 fuel does not visibly separated or visibly degraded in over 2 1/2 years, but the ethanol does evaporate out of the gas.  The end result is not a gummy fuel mixture, but simply one that has additives evaporate out and therefore would have a lower octane measure.

For a look at the testing of this batch of fuel when it was first purchased, click here.

For a look at the general effects of long-term storage of E10 fuel and the possibility of separation over time, click here.
For a comparative look at the results of ethanol content testing on non-ethanol race gas, click here.

Follow @PhaedrusStuff