Everything I’ve read says that the ethanol in E10 can absorb water…up to a point, after which, you can get phase separation and you end up with a blob of water and ethanol sinking to the bottom of the tank (I’m grossly paraphrasing here) which, of course, is not where you want it to be since you have a fuel pickup down there. A non-alcohol fuel additive can help disperse the water. Problem is worse in cold weather. So, best options appear to be to use a non-alcohol based fuel stabilizer and keep the tank pressed to avoid condensation. E10 fuel can go bad in as little as 30 days. There is a recent thread on here somewhere that covers this topic. Non-ethanol fuel should last for a year or more without issues. So my plan is to use a fuel stabilizer (I’ve chosen Star Tron, others use Sta Bil) and after each run, top off the tank with 100 octane non-ethanol fuel.
From West Marine:
“When E10 gasoline comes into contact with water, ethanol will allow fuel to absorb some or all of that water. This is actually somewhat beneficial, but fuel can reach a saturation point and water can phase separate to form a distinct layer in the bottom of the tank. The upper “gasoline” layer will be depleted of ethanol and have a reduced octane level. The lower “phase separation” layer will be a corrosive mix of water and ethanol. No chemical agent or fuel additive can be added to E10 gasoline, in a reasonable quantity, that will fully prevent phase separation or recombine a phase-separated layer.
Winter storage of ethanol-blended gas
Seasonal storage with E10 fuel is another likely time for problems. During storage, fuel will tend to oxidize; it will become “sour”, and may absorb water from condensation. Water-holding capacity of E10 fuel is reduced with lower temperatures, so phase separation is more likely with winter temperatures. E10 can hold approximately 0.5% water at 60°F (.64 ounces in a gallon, or 12 ounces of water in a 20-gallon gas tank), but can only hold about 0.35% water at 20°F (.45 ounces in a gallon).”
Anyway, I may be going overboard (note the nautical reference), but it will give me piece of mind. I’m sure others have different ways of dealing with this issue. As I said, I don’t plan to store the car all winter…I plan to drive her when possible, and if she does have to be laid up for a month or two due to weather, at least she will be protected as best I can. At least I think so?