Ethanol is an oxygenator in fuel, in gasoline. That means it helps oxidize everything it comes in contact with. To oxidize is to burn, to corrode, and to chemically react with what ever it comes in contact with. Sometimes that chemical contact is good, when it comes to the fuel actually burning, doing work, and moving you down the road. The rest of the time, that chemical contact is bad, very, very bad, for everything else in your fuel system. That it's an oxidizer makes it very, very unstable and prone to want to chemically react with everything it comes in contact with until it itself is burned and consumed.
