Originally Posted by N427EF
If I read that post correctly the op used 100LL or ethanol free mogas on that engine.
It is precisely why that kind of corrosion formed because the water in 100LL and ethanol free mogas separates out and settles in low spots in the fuel system. As someone pointed out in that thread, ethanol mogas keeps the water in suspension and it passes harmlessly through the combustion cycle.
At some point, if there is enough water in the fuel, the ethanol can not absorb any more water and the ethanol comes out of suspension (the weight of the absorbed water?). If memory serves me correctly when this occurs it makes the fuel look cloudy.
As to the corrosion: If E0 - is corrosion caused by water that can be sumped out of the low points in the fuel system and is so removed;
if E10 (or greater), is the corrosion caused by the constant presence of water that can not be sumped or removed. Water is still water, even if held in suspension, and the water is in constant contact with parts not expecting a visit.