Hollis- forgive me if it sounds like I'm telling you how to build a clock when you only asked for the time, but I want to be clear.
In the days before ethanol-blend fuels, even tiny amounts of water would drop to the bottom of a gas tank. You ran the risk of sucking that water into a fuel line, freezing and plugging the line in winter. Adding an alcohol (methanol, ethanol, isopropanol) would re-suspend that water in the fuel and avoided the freezing problem. Hence, DryGas.
With ethanol blend fuels, we have that protection built in. When larger amounts of water get into the fuel, it can still drop to the bottom of the tank, but now as an ethanol/water mix in larger volume. This does two bad things- it reduces the octane of the fuel layer and gives you a water layer that no reasonable amount of added alcohol will re-suspend. When ethanol is first added to gasoline, the ethanol is dry- no water. But, it's practically impossible to keep water from getting into the fuel eventually.
Methanol, ethanol and isopropanol are all hygroscopic- it's only a matter of how much. If I had to guess, methanol would be the worst. Methanol and ethanol have the added problem that they can be oxidized to formic and acetic acid (respectively, both known as carboxylic acids), which will corrode metals in the fuel system. Isopropanol does not oxidize to form a carboxylic acid. If I had to add an alcohol, it would be isopropanol.
Last edited by yarcraft91; 06-17-2012 at 09:01 AM.