fill the gas tank for winterizing?

just curious to see who all fills the tank before letting your boat sit idle for about 5 months? i've read in a few places that it is good to fill your tank all the way up, to prevent moisture from forming. however, i've also been told that it is unnecessary. so what do you do? fill it up all the way and add stabilizer, or do you just leave the fuel level where it's at and add stabilizer?

fill it. Especially now. Gas prices are a lot cheaper than they will be next spring.

(Message edited by psudy on November 17, 2008)

I pumped mine out, gas was still $3.50, tank is plastic so I didn't see the need for 50 gallons to sit all winter.

There are plastic tanks in these boats and they do not condensate, do put stabil in the gas though. Stabil has a new formula out for inboard boats, it has chemicals to counteract the ethonol effects on the engine.

An open compartment, whether it's a gas tank or a box will get condensation with temperature change if there is moisture in the air. The less air, the less condensation. Taping off the vent line would help some but a full tank has the least air and so the least opportunity to add water to your fuel system.
I add stabilizer, fill the tank, then drive the boat to the ramp so some of the stabilized fuel is in the lines.

If you have ethanol in your fuel it will absorb more moisture from the air than straight gasoline but the moisture it gets will not settle to the bottom of the tank. (unless you get a lot of water in there)

what about that heat stuff that removes water from gas tanks

I'll have to dissagree Art condensation is a myth and not an issue. Here is an article for you to read that explains exactly why.

http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

Gasoline goes bad over time, but Sta-bil helps. Why waste good fuel? So add enough Sta-bil to maintain the fuel you have left in the tank, run the engine to get Sta-bil in the lines and then store it. Fill the tank with premium in the spring to get the octane back up or else you could get knocks. I've done it this way for years. The condensation thing is bogus.

I left it only 1/4 full. Don't want stale gas, why waste 30 gal? Never hurt my old boat I/O in 15 years.

I Keep it almost empty and then add fresh gas in the spring. I just hope gas doesn't return to $4.00 before then

I have read the article about condensation and feel that it is likely correct, although we have large temperature swings in Florida with the passing of a cold front. We can go from the 30's to the upper 70's in one day. With that said, I keep my tank full at all times. This might be more of a function of wanting to let the boat down of the lift and be ready to go. I am fortunate to be able to use my boat all year without the need to winterize in central Florida.

I have a very good friend who was a chemist for Mobile Oil and he says that the shelf life is longer than the dormant period of winterization. The benefit of a Stabil type of product is more for the gums and additives that may clog up things, especially if you have a carberated engine.

I have always topped it off, stabilized it and have never had a problem. Condensation is debatable, but $1.89 gal in Nov isn't.

Dennis I agree I work in the industry and we have petroleum storage tanks with thousands and thousands of gallons of refined product that sits there just incase of an upset so that distribution isn't impacted. This product is stored for long periods of time. However the gasoline in your tank will not make the same temperature swing as the air did in that same 24 hour timeframe.

(Message edited by 05mobiuslsv on November 17, 2008)

Earlier this fall, I asked this very question of the manager of a major marine repair facility. His facility stores well over a hundred boats each winter. He gets this question all the time. He used to say store it full, now they advise:

If you have ethanol in your gas, store it as empty as possible.
If you have ethanol free gasoline, store it full with Stabil.

^^^^thats what we tell our customers ethanol=no good

I read the article. It was interesting and several of the points described are likely places for water to enter the tank. Over the season of operating they are more likely sources of water in the tank than condensation.
On the condensation argument I disagree with several points. I have seen the temperature increase in the city I live in rise more than 60°F in a day. It's rare to change that much but it does here so the temperature can go up more quickly here than it can go down. I have seen sweating and dew on my seats on a daily basis so it appears his assumption that fuel tanks can't trigger this is in error. All that needs to happen is that the relative humidity changes and condensation can happen. If it does the water drops below the fuel as it is heavier and the air in the tank is drier. The vent tube allows the relative humidity in the tank air and the exterior air to equalize (slowly) and the possibility of more condensation exists. Let's say it's only 1/10 of an ounce that might get in in a day. My off season is more than 240 days. That would be over 24 ounces of water.
I know I'd get nowhere near that. So it would be less than my hypothetical number, but it does not have to be much to create a problem that could be avoided.
Oh well, if you ask enough people their opinion someone will always tell you what you wanted to hear. That's what make the internet in interesting place to gather information from.