Remember that
ethanol is a water attractant and can
Phase Separate when saturated.
Almost full seems to be the easiest way to go which makes for less breathing of the tanks and you avoid the headache of working to get a tank completely empty.
Informative BoatU.S. Article below:
E-10 in Winter
Recommendations on Storing Ethanol-Enhanced Gasoline
For better or for worse, a shotgun wedding took place this past spring between boat owners and ethanol-enhanced gasoline. Everyone wore black. Now, almost four months into the honeymoon, it seems that at least some of the warnings of matrimonial acrimony may have been premature.
The key word is some. The fiasco with deteriorating fiberglass tanks (
Seaworthy January and April 2006) has certainly been painful for owners of many Bertrams, Hatterases, and other, typically high-end, boats. As of this past September, BoatUS Technical Services has documented over 70 reports of failures, including leaking tanks and wrecked engines, from both coasts and Hawaii. In all cases, tanks had to be replaced.
But what about the widespread reports of clogged filters that boat owners on Long Island Sound experienced when ethanol was introduced there two years ago? Why does there appear to have been fewer complaints of clogged filters when ethanol began arriving last spring at pumps throughout much of the rest of the country?
John McKnight at the National Marine Manufacturers Association (NMMA) speculates the answer has to do with preparation: Boat owners in 2006 were better prepared for the arrival of ethanol than boat owners on Long Island Sound were in the spring of 2004. That's not to say that boat owners in other parts of the country haven't had plenty of problems this year, but there is now a widespread consensus on how best to cope (see "
Making the Transition to Ethanol").
Avoiding Phase Separation
Another, perhaps larger, test will come this winter when boat owners prepare their boats for seasonal lay-up. One of the unfortunate properties of ethanol is its ability to attract and absorb water. Ethanol-enhanced gasoline can absorb roughly 10 times as much water as MTBE and still burn safely through the engine. But if ethanol becomes saturated, which can happen when it sits for long periods, the ethanol separates from the gasoline, forming two separate solutions. This is called phase separation and it's bad news for the engine. An engine won't run on the (water-soaked) ethanol solution, which sinks to the bottom of the tank and is highly corrosive.
There is no quick fix. When MTBE becomes saturated with water, it remains chemically bonded to the gasoline — MTBE doesn't phase separate — and a water separator can eliminate the excess moisture. With ethanol-enhanced gasoline, however, once phase separation occurs, additives and water separators can't help;
the only remedy is to have gasoline/ethanol/water pumped from the tank.
While all of this may sound discouraging to anyone planning to lay up their boat with ethanol in the tanks over the winter, the good news is that E-10 has been a fact of life in certain areas of the Midwest for several years and there have been relatively few problems.
Seaworthy talked to several marina operators, surveyors and boat owners in the Chicago area who had the same reaction to ethanol: "It's no big deal."
No big deal? How can E-10, which attracts moisture and can fall apart, be expected to survive the winter? With any fuel that will be sitting for a long time, it is important to add stabilizer — an antioxidant — to extend the life of the fuel. (E-10 and gasoline with MTBE have the same shelf-life — roughly a year.) What a stabilizer won't do, however, is prevent phase separation. Just how you do that is subject to some debate. Several sources, including one prominent engine manufacturer, recommend running the tank down to almost empty and then adding stabilizer. The following spring, the tank can be refilled with fresh gasoline. Lew Gibbs, a senior engineering consultant at Chevron, worries that leaving a few gallons of gasoline might attract enough condensation to cause phase separation. If that were to happen, the highly corrosive ethanol/water mixture would settle to the bottom of the tank and would remain there even after the fresh fuel was added in the spring.
Gibbs said his first choice would be to completely empty the tank when the boat is laid up and then refill it the following spring with fresh gasoline. No ethanol = no ethanol-related problems. Unfortunately, completely emptying a built-in tank safely is nearly impossible. His next choice, one that's more practical, is to top off the tank to 95% full (to allow for expansion). A tank that's almost full reduces the flow of air into and out of the vent, which reduces condensation on tank walls. Any condensation that does form will be absorbed by the gasoline. (Note that the National Fire Protection Association [NFPA] also requires tanks to be topped off to minimize explosive vapors.)
Gibbs said the worst choice, which was confirmed by marina owners in the Midwest, is to leave the tank half-full over the winter. Jerry Metzger, the general manager of Chicago Harbor's nine marinas, said phase separation problems typically occurred when boats had been stored over the winter with tanks that were a quarter to half full. The tanks breathe more and attract larger amounts of moisture. Metzger says boaters in the area have learned to fill the tanks before the boat is laid up for the winter.
Note, however, that phase separation can occur anytime E-10 sits for a long time. On Long Island Sound, which has been using ethanol-enhanced gasoline for the past couple of seasons, Mitch Kramer at TowBoatUS Oyster Bay said they haven't had any problems with their own boats, which are used every day. Kramer says the problems now on Long Island Sound seem to be with boats that are used infrequently. Perhaps because of high fuel prices, some owners don't use their boats as often and are also less likely to top off their tanks. Half-empty tanks that sit for long periods are more likely to attract moisture, which causes phase separation. The key: Use your boat!
One final note: DON'T try to plug up the vent to prevent moist air from entering the tank. Without room to expand, the additional pressure could rupture fuel system components.
Preventing Phase Separation Do's and Don't's
DO
- Add Stabilizer
- Top off the tank (to about 95% full)
- Use your boat frequently during the season so that gasoline doesn't go stale in the tank
DON'T
- Leave the boat's tanks partially filled
- Let the boat sit idle for months over the summer.
FWIW
Goblin
