Plan "B" For Winterizing Boat Fuel

Every year at this time almost every outdoor magazine runs a story about how to winterize your boat and boat engine. That’s for good reason because there’s nothing more frustrating when spring arrives after a hard, Indiana-style winter than heading down to the lake for the first outing of the spring and having your motor either not start or run so poorly you worry about heading out at all.

Winterizing instructions always include the advise to top off your fuel tanks and add the proper amount of fuel stabilizer to keep the gas from going bad. You’d think the stuff would last forever, but fuel experts claim gasoline starts losing pep (octane) and undergoes other chemical changes as soon as you pump it. In a month the difference is slight, by two months it can be measurable and noticeable to the person using the fuel.

By filling the tank to the top, less of the fuel is exposed to the air and the normal oxidation process of the gasoline slows. Adding a proper amount of fuel stabilizer is supposed to further reduce the aging process.

A topped-off tank is less subject to condensation which occurs when moist air contacts the cold interior of the tank and loses it’s moisture in the form of condensation which drips down the inside of the tank and sinks to the bottom. Gas and water don’t mix and it’s no fun re-proving this principle at the boat launch next spring.

Last year, I learned of an alternate method which seemed to make sense and I tried it. My boat has a 70 gallon tank which means it takes a lot of fuel stabilizer to treat the fuel- almost a quart. Fuel stabilizer is somewhat expensive. If I can find it in quart containers the price is about $20. If I have to buy it in the sizes most stores carry, it’ll cost twice that.

The main reason I tried the new method is because I’ve never thought my engine runs really well on stabilized fuel when I take it out in the spring. I’m sure it runs better than if I’d not added any stabilizer, but it idles poorly and coughs occasionally at trolling speeds. (When I get it out in the spring, I’m there to run at trolling speed, not to go speed-boating in 40 degree weather.)

With 70 gallons in the tank and since early spring fishing for me means easy fishing, not running all over the lake, I may only burn about 10 gallons on a typical outing. It takes several trips to make room for enough fresh gas before I start noticing any performance improvement.

The alternate method I learned last year flies in the face of the “top off the tank for winter” method. With this method, in the fall, I run the fuel in the tank down almost to empty, stabilize what fuel is left and store the boat for the winter.

What about condensation? For one, I have a plastic gas tank in my boat. I don’t know for sure, but I’d guess condensation occurs less with a plastic tank than it would on a metal tank. Less isn’t none so come spring I head for the gas station and fill up the tank with high octane fuel. The boat runs just fine on 87-grade, but I figure the 91 gives the small amount of last-year’s fuel a boost. Then, I dry out any condensation in the tank using a gas-line antifreeze product containing methyl alcohol. (Use a product containing isopropyl alcohol if you have a fuel injected engine.) The label on these bottles will list how many ounces to use per gallon or 10 gallons of gasoline. The alcohol is like a liquid sponge and soaks up water molecules.

The last line of defense is a water separator in the fuel line. Not all boats have these, but they are available as add ons. I checked the separator on my boat after about half the first tank of fuel was burned. There was no water so I assume either there wasn’t much to begin with or what was there was cleaned up by the antifreeze.

I’ve used this method for several years now and my engine never has the “spring-sputters” anymore. I hit the switch, it fires right up and runs like I filled it up at the refinery.