Expanding ice should not be a problem if the water is in small quantities compared to the size of your tank. If you had an inch or two of water in your tank expansion might be a problem. But if that’s the case you would have to clean your tank anyway. The problem with the ethanol base fuel is that it does not separate with water like the old MTBE base fuel. It doesn’t completely mix with water either though. Water just sort of suspends within the fuel. This is why conventional water separating fuel filters will not work as well with the ethanol. The water doesn’t just separate in the filter due to the differences in density. The other main problem with a full tank would affect older or more neglected fuel systems. The ethanol acts as a mild solvent and will slowly work on releasing the varnish buildups throughout your fuel system. Leaving the fuel in for months only worsens this problem and gives it more time to work.
This is a double edge sword for the first few seasons with this new fuel. I would recommend a full tank to reduce the moisture buildup but if you do this you should be checking or changing the filters very regularly (every tank or so until you see very little crap in the filter). This method will keep the moisture buildup down to a minimum anyway. Just like we used to do with old fuel. Don’t leave it half full because this will result in both problems occurring. If you leave it empty, in the spring before filling, try to check for water or pump it out. A totally empty tank is never really possible anyway. My feeling is that the manufacturers are recommending empty just because they don’t know what will happen (and neither do we).  |