GulfSea said:
seasick, you can see condensation science on a poorly insulated window of a house. Maybe even observe rotted wood around old windows from that same condensation. I'm not beating you up or trying to argue but it does happen inside tanks and should be considered to avoid phase separation of ethanol blends. Yes, E10 does like water....but enough of it and the nightmares of phase separation can begin. I lost 3 yard equipment carburetors and a 30 year old chainsaw to the stuff about 4-5 years ago so the bitter taste is still there.
I now use E10 because the non-ethanol stuff is just too expensive (35-40% more) to use. But I keep the fuel fresh, only buy from the same busy station and change filters way more often than required to keep an eye on what's going through the system.
I too have seen yard equipment carbs ruined by bad gas, perhaps it was water, maybe is was just old gas. The reality is that if you calculate how much water can condense inside a tank vented to the atmosphere, even with enormous temp swings and high humidity, the amount of water is relatively small. yes, the cycle will repeat and that can add more moisture but a boat tank and a carb can't be compared to a window that is quite warm on one side and not only cold on the other, but exposed to quite a large supply of moist air.
You also need to admit that the moisture in the air in a tank can also be pulled out by the addition of drier air. The cycle works both ways.(Granted, water that is absorbed by the ethanol is permanent)
For phase separation, you need a lot of water by volume to gas.
I suspect that for whatever reason, small containers of gas go sour faster than larger ones. That may explain why we see issues with yard motors more that I have seen with boat tanks. The key here is TANKS. I do drain filters and fuel reservoirs during long storage and many owners at my facility will 'winterize' carbs by draining the gas and filling the bowl with Marvel Mystery oil. That serves too purposes; it reduces corrosion from moisture and for older machines, it helps protect the gaskets from drying out.
My point is that I have experience with over 50 vessels at my club and we just don't see a lot of condensation issues with partiality filled tanks over the winter. Most owners do not top off their tanks before storage and I don't recommend they do. The reason is simple: Should something go bad like a water intrusion issue, come spring they have to get rid of a lot of fuel that cost a lot to buy AND they have to pay for the proper and legal disposal of the gas and that cost dearly.
Just my two cents.