Ethanol-laced gasoline poses a problem for boats that spend the off-season in storage.
Opinions vary as to whether to store tanks empty or mostly empty, or whether to store them around 95 percent full.
The theoretical benefits of empty or mostly empty tanks, according to some experts, is that if there's no ethanol in the tank it can't absorb water, with the resulting possibility of phase separation. And it can't dissolve old deposits in the tank.
The theoretical benefits of a full tank, according to other experts, is that there's less likelihood of moisture forming in the tank from condensation and that a topped-off tank minimizes the highly explosive fumes that can remain in an empty tank. (The National Fire Protection Association calls for tanks to be topped off to minimize explosive vapors.)
Theoretically, the best solution would be to completely drain and clean your fuel tank for winter storage, says Erik Klockars, technical consultant for Soundings. But that's not the real world. It's virtually impossible to remove all the fuel - it costs from $5 to $9 per gallon to dispose of old gas - and fire marshals want to see tanks full because of the danger of explosion from fumes, Klockars says. Many marinas share the same concerns about explosions, particularly those with rack storage.
The next best thing is to store the boat with the tanks around 95 percent full, using the highest octane gas available to hopefully compensate for octane loss resulting from winter storage, Klockars says.
He also emphasizes treating the fuel within the engines for storage. He mixes his own proprietary "concoction," which includes stabilizers and other chemicals, and runs it through the engine from a small tank. If you want to try this, he says, consider filling your fuel filter with high-test fuel, a stabilizer and additives, and running that through the engine. (Be aware of the possibility of explosion when working with gasoline; use the right equipment and follow safe procedures.)
In addition, he suggests that during the boating season it's best to use your boat as much as possible, filling up the tank when you leave the dock rather than when you return, and using appropriate fuel additives and a good decarbonizer.
And diesel? It doesn't contain ethanol, so those problems aren't an issue. To prevent condensation, most experts agree that it's best to store boats with diesel tanks around 95 percent full. Remember, if you plan to store your boat ashore with the tanks nearly full, the boat must be hauled and blocked in such a way that the weight of the fuel won't damage the boat, and the boat must be built to handle this.