Is It's Hygroscopic (ATTRACTS WATER LIKE MAD) nature.
It will pull environmental moisture in through the Vent System of Fuel Tanks.
Then as the Fuel "Sits" (sometimes for as little as 48 hours) the Ethanol/H2O
SEPARATES OUT of the Fuel Mixture ["Phase Separation"] to the Bottom of the System.
So the FIRST sip the engine gets is not fuel but the Water/Ethanol mixture.

The Extreme Corrosion effects seen in Ethanol systems is due to the WATER
/Ethanol mix.

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'84 300SD sold
124.128