Even under ideal storage conditions, E10 gasoline has a "shelf life" of just 30 to 45 days. After that the ethanol and gasoline start to go their separate ways. During the season this isn't a problem as long as you use your boat often and run the tank as low as you dare before refueling so the gasoline is always fresh. But winter is almost here. What'll happen to the E10 in your tanks between now and spring? Whatever the answer, it ain't good. Here's what you can do now to minimize problems next spring.
As E10 breaks down, it leaves lower-octane gasoline on top of a layer of ethanol and/or a mixture of ethanol and water. (For more information, see "Around the Yard," May 2007.) This is called "phase separation," and the slurry under the gasoline is called "water bottom." Even if your tanks were water-free at lay-up, by spring there could be substantial water bottom because of the short-lived E10 breaking down. If the water bottom gets into the fuel system, it can cause problems (no surprise there). Good filters are then your first line of defense; if you've been running E10, you probably already have them.
But here's the rub: The water bottom will have a concentration of ethanol higher—maybe much higher—than the ten percent by volume of fresh E10. And high concentrations of ethanol can be corrosive to aluminum and some fiberglass fuel tanks. In fact, the American Coalition for Ethanol warns against using aluminum, brass, or other soft metals anywhere in the fuel path when handling E85 flex fuel (in use in some parts of the United States but not, so far, in boats). E85 is 85 percent ethanol—but at what concentration of ethanol does the damage begin? I don't want to find out, and I'll bet you don't, either. Instead of turning your boat into a science project, stop, or at least delay, phase separation by adding a nonalcohol fuel treatment to your E10 gasoline.
All the usual suspects—Star brite, MDR, CRC, K100, and so forth—are available at any decent marine store and contain an E10 fuel preservative. MDR claims its E-Zorb can prevent even reverse phase separation. Bill Lindsey, vice-president of marketing for Star brite, said his company's E10 additive, Star Tron, can stabilize E10 for up to one year. Here's how it works, according to Lindsey: "Star Tron enzyme fuel additive prevents phase separation by deionizing the fuel, which in layman's terms means neutralizing the electrical charges between water molecules. The deionization process breaks the electric bonds of the water molecules to prevent them from forming into large clusters or drops that then settle to the bottom of the tank. Thereby, the octane rating is left intact and the smaller, micron-size, suspended water molecules can be burned safely, right along with the gasoline portion of E10." Lindsey recommends adding Star Tron to E10 all the time, not just during lay-up; it helps keep the gasoline up to spec and to clean the fuel system as well. The Ethanol Promotion and Information Council agrees, suggesting the use of a fuel stabilizer any time E10 will sit in the tank for more than a month. (See the guide to boating with E10 from Ethanol Promotion and Information Council.)
The bottom line: If you want E10 to stay young over the winter, give it a drink from the fountain of youth by adding a fuel treatment in the fall.
Should I store my boat with the gas tanks full or empty? A while back you mentioned that folks running E10 might be better off storing empty. I'm using old-fashioned gasoline, but doesn't it go bad over the winter, too?—P.F. Webber, via e-mail
For decades yards and their insurance companies have insisted on nearly full tanks aboard winter-stored, gasoline-engine boats, leaving just a little space for liquid expansion without leakage through the vent. This minimizes explosive gas fumes; less air in the tank also prevents condensation from adding water to the gas, but safety is the main reason. And you're correct—even nonethanol gasoline left for five or six months will deteriorate, but this is prevented with the addition of a fuel stabilizer. So the easy answer to your question is, do what your boatyard requires, no matter what you read here. Or find another boatyard.
Has E10 changed the way boatyards think? Apparently not: I surveyed half a dozen randomly chosen yards in states using E10, and all wanted tanks stored almost full. The Ethanol Promotion and Information Council agrees, recommending topping the tanks to 90-percent capacity and adding a fuel stabilizer. However, Dan Crete, head mechanic at Burr Bros. Boats, disagrees, as do many engine manufacturers. Crete has done a ton of research and hands-on testing of the effects of E10 gasoline on fuel systems, and his observations suggest the better practice is to run tanks down to quarter-full or so for storage, then add a fuel stabilizer. (Less gas takes less stabilizer, too.) Topping up with fresh gas in the spring rejuvenates the fuel that's slept aboard for the winter. Crete has been storing boats this way for the past seven winters, both pre- and post-E10 gasoline, with no problems. I think he's right, so unless your boatyard demands otherwise, it's the practice I recommend. Just don't skimp on the fuel stabilizer.
This article originally appeared in the November 2007 issue of Power & Motoryacht magazine.