Leave tank full for winter?

[WindLove]

Should you leave your fuel tank full or empty when not sailing in the winter? I've heard people say that lessens the chance for bad stuff to grow, which makes sense to me, but someone with a lot of knowledge told me recently they like to start every season with "fresh fuel" and never fill at the end of a season.

Which is the most logical train of thought? Or is there really a difference.

[ontherocks83]

Filling it with fuel will stop condensation build up inside of the tank. I always top off the fuel and put in and additive to prevent growth and stabilize the fuel.

[Mike OReilly]

We always fill to limit condensation. We also use diesel stabilizer.

[Cheechako]

Conventional wisdom is to leave it full.... not sure if there is great merit in it or not though. These days the fresh fuel might be a better, or at least as good an option.
With the whole boat cold and unused will condensation be better or worse than when you are using the boat creating a large temperature difference inside the boat vs the seawater and tank?

[valhalla360]

First question is diesel or gasoline?

Second question is can you actually empty the tank?

While I don't like the idea of a full tank of diesel sitting thier, it's not to big a deal as long as there is no water already in the tank to grow things. Gasoline, especially with ethanol will go stale and the ethanol tends to attract water.

Ideally, completely empty and dry is the way to go. Unfortuantely, most manufacturers don't provide a convientent way to drain the tanks and partially empty is probably worse than full. We drain our tanks in the fall and check they are still empty in the spring before filling up.
- Totally empty and condensation tends not to form as there is no heat sink to create a temperature differential.
- Totally full, there is little air to form condensation so water in the fuel is less of an issue.
- Partly full, the heat sink of the liquid helps form condensation and then it finds it's way to the bottom of the liquid where it can't evaporate.

Of course, I think the condensation theory is largely a myth. If you look at the amount of air that enters and leaves the tank over the course of a day, not a lot of moisture ever enters over the course of an entire winter. More likely it is leaks in deck fittings allowing rain and snow melt to find thier way into the tank. A full tank of gasonline may mask this as ethonal can absorb a bit of water before phase seperation occurs, so minor leaks that only let in a small amount may not cause issues. On diesels, the water seperator may take care of a few ounces with little fanfare.

[WindLove]

Thank you everybody. I have always filled it....kinda made sense to me not have a bunch of air in a tank, but it sounds like there is at least some debate on it.

Originally Posted by valhalla360

First question is diesel or gasoline? .

Mine is diesel.....


Thanks!

[Stumble]

Frankly I think the real answer is either full or empty, but not half filled. A fully empty tank just takes a moment in the spring to wipe dry, and fill for the season. A full tank can't be cleaned, but significantly reduces condensation. The worst is half full since there is plenty of space for air to circulate and condense, while preventing dealing with a dry tank in the spring.

We don't take our boats out of service, but have installed a small (5gallon) day tank. The big tank is left bone dry, sometimes for years, until we do a long distance thing. The day tank hold enough for a few days at a time.

[ctl411]

Not sure where you are, but the farther north the less of a problem. Not much moisture in cold winter air.

[sailorboy1]

Last Fall was the first time I ever put the boat away with less than a full tank (was about 2/3 full). This spring was the first time the fuel filters ever clogged up, wonder if there was a relationship between the two

I'm rethinking whether it is worth the cost to install a fuel tank vent filter for moisture as a winter project. I think it is worth the cost if I can budget the time to do it.

[Tynesider]

This side of the Atlantic in the UK most sensible yachtsmen always fill there diesel tanks for the winter to prevent condensation if they are not going to use the boat.

However like many others I also sail 'all year round' winter or summer last year in -14C at times without any problems diesel wise.

However trying to furl a Genoa thats froze is another story

[Cotemar]

For Diesel fuel, you should always fill your tank to the limit condensation and use diesel stabilizer.
The reason you do this is because condensation forms in any air space during temperature changes.
It will rain in your fuel tank and then create nasty slim which will clog your fuel system.

With Gas fuel, you leave the fuel tank empty as the high alcohol content in modern gas will evaporate out or eat fiberglass fuel tanks causing even more problems than condensation.

[Maine Sail]

Originally Posted by Cotemar

For Diesel fuel, you should always fill your tank to the limit condensation and use diesel stabilizer.
The reason you do this is because condensation forms in any air space during temperature changes.
It will rain in your fuel tank and then create nasty slim which will clog your fuel system.

Hmmm 20+ years of draining my fuel tank and never once a single drop of water.... If tanks magically filled with water I guess we'd not need water wells... We could solve all of the worlds water problems by just setting out empty tanks...

An empty tank can't magically create water otherwise the empty Sabre fuel tank I have in my barn would be full by now, its bone dry and has been for a number of years........ My barn is hot, then cold, then hot, then cold, then hot and yet that empty Sabre fuel tank is still bone dry....

I simply drain the fuel tank and burn it in my homes boiler and then start next season with fresh fuel...

About the only thing I can think of as a benefit to filling the tank in the fall is if diesel prices go up over the winter.

This is the first year my tank may be left full, but I absolutely don't want to... I am trying to source a small day tank for my Espar and if I do then my tank will get emptied into my home heating oil tank as it has in years past..... I like to run the Espar in the winter to do work on the boat but I prefer my main fuel tank empty....

[Cotemar]

Really.
I wonder what this stuff is?
Air comes in fuel tank vent, bringing in condensation.

[Maine Sail]

Originally Posted by Cotemar

Really.
I wonder what this stuff is?
Air comes in fuel tank vent, bringing in condensation.

If the tank is empty it warms at the same speed as the rest of the boat thus nothing to "condense"... Go place an empty tank in an unheated shed, this simulates a boat very well, with a vent and let me know how much water is in it in three years....

I live on the coast so our air is pretty humid yet zero, zero, zero water ever in our tanks when emptied... Again I have an empty Sabre aluminum tank in my barn. The vent hole is open the rest of it sealed up. No water at all....

I have been doing this in the "real world" for over 20 years, no raining in my tanks, no water just real world results...

[ontherocks83]

Originally Posted by Maine Sail

I have been doing this in the "real world" for over 20 years, no raining in my tanks, no water just real world results...

And I've been filling my tanks for 20+ years and adding stabilizer without any problems, no need to be snarky about it. Obviously both ways work. However I will argue 10 ways to Sunday that filling your tank and adding stabil is oodles easier then draining it completely and lugging it home to use elsewhere.

Both are effective but I am going to go with and recommend the equally as good option that is way easier.

No need to jump on Cotemar's back about what his recommendation is. Especially since most people aren't going to go through the trouble of completely draining a tank so recommending filling it is a very good viable option.