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Full or Empty? Winterizing Your Performance Boat

The winterizing debate continues about how much fuel you should leave in the tank.

October 9, 2012

Go Fast Blog

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This time of year, you can guarantee that when it comes to one question about winterizing, you’ll get more divergent answers than during a political debate.

So I asked some of my local dealers the following question: “When you winterize a boat, do you put it away with the gas tank full or empty?”

MerCruiser and ValvTect Petroleum Products, which supplies the majority of “treated” gasoline to marinas in bulk, recommend that you fill your boat’s gas tank with fuel that contains an ethanol-combative treatment prior to winterizing it. Both suggest that you run the treated gas through your fuel system and engine prior to putting away the boat.

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Jerry Nessenson, president of ValvTect, said that his treated fuel will remain stabilized for up to one year.

READ: BOATING’S GUIDE TO WINTERIZING YOUR BOAT

Fuel needs to be treated because of ethanol that’s now added to gasoline. In what’s called “phase separation,” over time, the ethanol allows water that’s in the gasoline to separate from the fuel and sink to the bottom of the gas tank because the water is heavier. Then, because, the fuel pickup is almost always on the bottom of the tank, you’d be picking up water to suck into your engine’s combustion chamber, not fuel, which can cause problems.

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The school of thought on filling a fuel tank prior to winterization is that there won’t be any space in the reservoir for condensation to form in colder climates, such as my home in Maine. During condensation, when temperatures fluctuate, water can form inside the tank. Those who say to leave the tank lower than ¼ level say they’d rather deal with the small amount of water than results from condensation than a full tank of expired fuel.

The results of my poll were as follows. One local marina abides by the recommendations made by the boat brands it sells and suggests to its customers that they fill their tanks. Another independent engine shop, which is where all the go-fast guys in southern Maine go for work, wants between a half and quarter tank and stabilizes the fuel as part of the winterization service. Here’s the best one. The service manager at Port Harbor Marine in South Portland, Maine, Jim Peterson, said, “Ideal is empty, but if there’s anything above almost empty, we fill them.” Get this guy a podium at the next political debate.

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