Leave tank full for winter?

[ctl411]

Originally Posted by Cotemar

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

That's a oil fill on a car. What do I win lol.

[boden36]

I just took the top off our keel tank and cleaned the sludge out of it , first time in 25 years. There were droplets of condensate on the inside of the lid. The tank had been sitting nearly empty for some years.
Maybe condensation is worse when you are running the engine, because fuel return gradually warms the tank. When the tank cools it draws a lot of air in.
We are leaving our tank empty (unpainted steel) but I plan to flood it with argon to limit corrosion.
I have started using argon flooding for partially used paint containers too and it seems to stop deterioration of contents.

Regards,
Richard.

[Cotemar]

Mainsail,
I'm not discounting what you said, it's just that OP and others here have large fuel tanks and probably would not empty them at the end of the season. What I am saying is the vast majority of boaters with diesel fuel tanks filled them completely, because it's too much work to empty them of large amounts of fuel and transport that fuel home.

[Maine Sail]

Originally Posted by Cotemar

Mainsail,
I'm not discounting what you said, it's just that OP and others here have large fuel tanks and probably would not empty them at the end of the season. What I am saying is the vast majority of boaters with diesel fuel tanks filled them completely, because it's too much work to empty them of large amounts of fuel and transport that fuel home.

Then the obvious answer in that situation is to fill it full... If you have the easy opportunity, as I do, to empty it, then that is what I personally prefer.

Emptying the tank however does not cause it to fill with water, and that was my main point...

[Sailing Cowboy]

Either completely full or completely empty. I had 30 boats with motors and tanks in the northern climates and if the guides missed one tank storing in the fall and it was used in the spring guaranteed carb full of water.

[Maine Sail]

Originally Posted by ontherocks83

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.

Sorry I was not trying to be snarky just trying to answer the question, from a different angle, as it pertained to the OP's question. I then wanted to clarify that it would not be "raining" inside an empty fuel tank...

Originally Posted by 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.

I do prefer to empty my tank but it is easy for me to do that. By not leaving fuel in my tank there is nothing to grow, nothing to absorb water and no condensation. The OP seems like he could go either way on this. If it is not easy to drain your tank the best option is to fill it to full and consider installing a tank vent air drier such as an H2Out...

[rw58ph]

Originally Posted by 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.

That depends. If you can use/turn the new low sulfur diesel each year. If not than not filling them might be the best as the new low sulfur diesel does not have a long shelve live and the water separates out. So its not just a question of condensation but separation. If you tank is small and you can turn then full. Regardless of how full the tank is I would us additives that stabilize the diesel and/or absorbs the moisture/water back into the fuel. Polishing/cleaning the fuel also helps.

Also the age of the tanks might also have an effect how full the tanks. It might be smart to allow room in each tank to hold the fuel of the other tank just in case. The Eagle has three 400 gallon tanks that are 35 years old, which I keep at a maximum of 1/2 full. The reason is we can not use/turn 1200 gallons of fuel, short shelve live, and the age of the tanks.

Also knowing what kind of diesel it is, low sulfur, ultra low sulfur and or bio also has an effect. So it depens!

[WindLove]

Thank you everyone. I'm kind of In the leave them full camp, and yes, Mainsail, if I could empty them completely I can see how that would be ideal but that's not logical for me because the boat is in the water.

[LakeSuperior]

Originally Posted by Maine Sail

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...

The mechanism is as follows for a given airspace, no fuel:

1. During the day the increase in ambient temperature causes the tank walls heat and the air inside warms and expands. This expansion causes some of the tank air to move to the outside atmosphere.

2. In the evening/night the ambient air temperature cools and causes the tank walls and the air inside to cool. This causes a decrease in air volume drawing moist outside air into the interior of the tank.

3. As the evening air continues to cool it may cause the air in the tank to reach dew point temperature. At this point liquid water will condense on the tank walls and drain to the bottom of the tank.

4. During the day the cycle will repeat.

The key factor here is that the dew point inside the tank must be attained for condensation. The reduction in temperature of the inside of the tank is retarded by both the thermal mass of the fuel if present (it will tend to keep the inside of the tank at a more constant temperature) and the boat and stuff surrounding the tank. That is the tank inside the boat doesn't see the same temperature swings as the outside air.

If you are in the Midwest you will see extreme diurnal temperature variations in the spring and fall which will tend to cause more condensation. For example, the Pella windows with the interior sash do not work up here as they are vented and so suffer the fuel tank problem. They are no longer sold up in the north country.

If you are in a maritime climate then you don't see the big extremes and therefore don't pump as much water into the tank via the above described mechanism.

[captain58sailin]

I have always filled my tanks at the end of the season. Same reason as previously posted about condensation. Another consideration is the economics. I have never come into spring with the fuel costing less than in the fall. So I get one tank full of running before having to buy the newer more expensive fuel.

[valhalla360]

Originally Posted by LakeSuperior

The mechanism is as follows for a given airspace, no fuel:

1. During the day the increase in ambient temperature causes the tank walls heat and the air inside warms and expands. This expansion causes some of the tank air to move to the outside atmosphere.

2. In the evening/night the ambient air temperature cools and causes the tank walls and the air inside to cool. This causes a decrease in air volume drawing moist outside air into the interior of the tank.

3. As the evening air continues to cool it may cause the air in the tank to reach dew point temperature. At this point liquid water will condense on the tank walls and drain to the bottom of the tank.

4. During the day the cycle will repeat.

The key factor here is that the dew point inside the tank must be attained for condensation. The reduction in temperature of the inside of the tank is retarded by both the thermal mass of the fuel if present (it will tend to keep the inside of the tank at a more constant temperature) and the boat and stuff surrounding the tank. That is the tank inside the boat doesn't see the same temperature swings as the outside air.

If you are in the Midwest you will see extreme diurnal temperature variations in the spring and fall which will tend to cause more condensation. For example, the Pella windows with the interior sash do not work up here as they are vented and so suffer the fuel tank problem. They are no longer sold up in the north country.

If you are in a maritime climate then you don't see the big extremes and therefore don't pump as much water into the tank via the above described mechanism.

This is where my theory that condensation is a myth comes in.

At 50% humidity normal pressure and temperature of 5C, 1 cubic meter of air contains approximatley 2.5 grams of water. So assuming you have a large 500 gallon tank half full there is around 1 cubic meter of air space.

If we assume the air is completely replaced once a day for a 180 days and every last molecule of water is condensated out, you get around 450 grams of water from condensation.

This is overstating the condensation by a large amount.
- With a small vent, maybe 25% of the air is turned over each day due to thermal expansion of the airspace. This is the only source of additional water, so we are down to around 112 grams of potential water from condensation.
- If the outside air averages around 50% relative humidity, cooling first raises the relative humidity before creating condensation. Even when condensation is created some of the moisture always remains in the air. That further reduces the amount of condensation created. Probably by at least another half. so we are down around 60 grams of potential water from condensation.
- In the morning, a large percentage of the condensation will still be on the walls and ceiling of the tank (at very cold temperatures, the water will form frost and almost none will make it into the fuel. As it warms, this moisture will largely evaporate, so you are down to maybe 10 grams of potential water from condensation.

10 grams is still likely a worst case senario as most boats have much smaller tanks and even in Michigan we only store the boat for 5 months at a time. Further south it would be even less time.

So while a dry tank would have those 10 grams evaporate, even if there was fuel, it's not likely enough to overwhelm your water seperating filter.

This leads me to the belief that water in fuel problems are far more likely to be coming from other sources than condensation such as a leaky fuel fill.

[captain58sailin]

Good point, my aim is to elimnate all possible sources of contamination. Most times when I have an engine problem it goes back to the fuel supply. When I am using my engine, I am usually in a situation where it is needed and having it fail would be a bad thing.

[LakeSuperior]

Originally Posted by valhalla360

This is where my theory that condensation is a myth comes in.

At 50% humidity normal pressure and temperature of 5C, 1 cubic meter of air contains approximatley 2.5 grams of water. So assuming you have a large 500 gallon tank half full there is around 1 cubic meter of air space.

If we assume the air is completely replaced once a day for a 180 days and every last molecule of water is condensated out, you get around 450 grams of water from condensation.

This is overstating the condensation by a large amount.
- With a small vent, maybe 25% of the air is turned over each day due to thermal expansion of the airspace. This is the only source of additional water, so we are down to around 112 grams of potential water from condensation.
- If the outside air averages around 50% relative humidity, cooling first raises the relative humidity before creating condensation. Even when condensation is created some of the moisture always remains in the air. That further reduces the amount of condensation created. Probably by at least another half. so we are down around 60 grams of potential water from condensation.
- In the morning, a large percentage of the condensation will still be on the walls and ceiling of the tank (at very cold temperatures, the water will form frost and almost none will make it into the fuel. As it warms, this moisture will largely evaporate, so you are down to maybe 10 grams of potential water from condensation.

10 grams is still likely a worst case senario as most boats have much smaller tanks and even in Michigan we only store the boat for 5 months at a time. Further south it would be even less time.

So while a dry tank would have those 10 grams evaporate, even if there was fuel, it's not likely enough to overwhelm your water seperating filter.

This leads me to the belief that water in fuel problems are far more likely to be coming from other sources than condensation such as a leaky fuel fill.

I will digest what you are saying in detail. That said, my old Pella windows had standing water at the bottoms in the spring and fall and they had to be replaced. Pella stood by their product replaced them all at great expense with sealed blanks at no charge to me.

[thinwater]

The answer based on lab and field testing is that it requiress VERY specific conditions to accumulate water from the air, but these conditions do occationally occur.

No, an ampty tank is not similar to a 1/2 full tank. In an empty tank, condensation evaporates during the day yielding no net accumulation. In a 1/2 full tank the water drops to the bottom and does not re-evaporate if--and this is the important part--the fuel cannot simply absorb the water. Virgin fuel has a very small but signifigant ability to disolve water.

The thing is it depends on:
* How dry the fuel was.
* How full the tank was.
* Size of the tank (smaller tanks are more vulnerable).
* Temperature swings (Spring and Fall are most troubling, mostly Spring).
* Humidity and water temperatures (50% is low for boat in the water, 100% at night is more common).

In some tanks I could create haze and a few drops in the bottom, and in some not. Never enough to be important and it ALWAYS redisolved when the temperature rose. Thus, you would be very unlikely to ever see it.

However, corrosion rates and bio-growth both increased even without free water, as the disolved water content rose, so keeping out disolved water is also important.

What to do (in order of importance, IMHO).
* Check your filler cap and vent. Most common problem, by far.
* Install a good filter separator.
* Buy from a high volume outlet.
* Burn enough to fuel to change the tank 2x per year. You change your oil, don't you? I understand this is a real challenge for some large tank boats. See my last suggestion. And cruise more.
* Use an additive that prevents corrosion (steel or alluminum tanks).
* Use an additive that prevents bio-growth.
* keep the tank full.
* Consider a fuel tank vent filler. Cheap insurance and they work.

-----

What to do with gasoline tanks is a whole nuther issue. However, I will start with the fact that many yards (the one I use and several other is town) prohibit emptying gasoline tanks in dry storage; the explosion risk is greater and the insurance company says NO.

For gasoline the questions are different, but without getting long winded, empty for very small tanks and full with a vent filter for larger tanks. 1/2 tank is pure trouble.
-----

I'm assuming Cotmar understands that water in the crankcase is from blowby (burning fuel makes CO2 and H2O), not the atmosphere.

[valhalla360]

Originally Posted by LakeSuperior

I will digest what you are saying in detail. That said, my old Pella windows had standing water at the bottoms in the spring and fall and they had to be replaced. Pella stood by their product replaced them all at great expense with sealed blanks at no charge to me.

There may be a flaw in my theory...

But windows in a heated house are a much different senario:
- There is a continous temperature difference (although it does vary over the course of a day) and heating systems tend to move air around. This can result in continous formation of condensation (in particular around the frame of the window).
- Warm air hold much more water than cold air (going from 5C to 20C it is around 4 times as much).
- Given that the failure is probably pin hole sized, I see no way enough air could transfer in and out of the window to introduce a significant volume of liquid water.

I have a strong suspicion that with double pane windows, it's not air introducing the water in vapor form but rain/snow covering the break in the sealant. As the airspace cools, it creates suction drawing the already liquid water thru the break in the seal. Once inside, it travels around and manafests as condensation