Empty or full?

[Pete_G]

With the big ethanol fuel scare this year how are you leaving you boat's tank this fall, empty or full?

Very mixed messages out there, with one boat builder saying full and another empty. Engine manufacturers are also saying different things...

Parker Marine for example is still recommending full tanks with fuel stabilizer while many others are recommending empty tanks on account of ethanol.

[ChiefLinesider]

If you have an outboard emptying the tank would be the safest route. No moisture buildup, or breakdown of fuel to worry about.

Inboard- Near topped off/fuel stabilizer. (We will be doing this during the winter with Twin Yanmar Diesels.)

Hopefully this helps slightly. Sounds like you have been getting the same run around on the correct procedure. I would go with the manufacturers reccomendation.

[Pete_G]

The issue with an empty tank would be condensation though. That's part of the reason to fill the tank going into the winter. A quick air temp change in an empty tank and there's the possibility to have condensation.

We're going with the boat manufacturer's recommendation, but it's tough not to feel like it's a damned if you do, damned if you don't situation. Spring will tell.

[ChiefLinesider]

Just curious, what was it that they recommended?

Damned if you do, damned if you dont is right on. (Full tank) Ethanol pulls water into tank, possible fuel breakdown. (Empty tank) condensation. I read "a cupful of water in the tank in the spring a lot smaller problem than 50 gallons of bad gasoline". But if science class taught me anything I would guess that would mean cracked something or other if that water froze? Is that your concern with the empty tank scenario?

[Pete_G]

Not really. We're going the recommended empty;full tank on the boat is 150 gallons, that would be a LOT of bad gas.

Hadn't thought of the expanding ice though.

[merch]

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).