Top Up Tanks For The Winter?

[Ducati]

Is it really necessary to top up the diesel fuel tanks when we put our boat away for the winter?

I was going to just add some fuel conditioner and leave them 1/4 full.

Comments?

 

[tomlang63]

I always top off my diesel tank for the winter to prevent moisture buildup in the tank. I drain all water tanks and fill with antifreeze, and run through all the water lines to remove any left-over water. I also know some folks who drain their tanks completely and use compressed air to remove any remaining moisture, but I have never attempted that. Living here in the northeast, with pretty cold winters, any ligquid that can freeze is a potential problem.

 

[walmsleyc]

Dig through the archvies ...

There has been extensive discussion about this. I'm sure you will find some in the archives.

Some of the discussions took into consideration the potential moisture content of the air in the tank, the heat content of the fuel relative to the air, boat, surroundings, the local climate conditions during the storage period, daily temperature swings, condensation factors, etc. The gist was to establish that winter condensation was unlikely.

Here's one thing to consider. All Diesel engine owners should have a good fuel filter, and that filter likely has a water trapping design that can and should be checked and drained regularly. Unless winter condensation produces large amounts of water, you probably wont have a problem either way.

I typically fill up my tank for winter anyway, and I always drain off a few table spoons of watery crud from my filter a couple of times per season. I can't identify the source of this water, but a full tank over winter didn't prevent it.

Chris

 

[Don S/V ILLusion]

Everything I've ever heard about topping off the diesel tank is theory. It might help minimize condensation, it might not, but it will certainly create old fuel and diesel doesn't age well. If you use the boat enough to burn the tank contents quickly, it may not matter but most sailors don't use that much fuel.

Don't be concerned if water does accumulate. Another theory is that bacteria grow at the fuel/water interface. If that were true to any significance, we'd all have a major problem - the tanks at the oil terminals ALL have water bottoms intentionally to preclude fuel leaking out the bottom before it is recognized.

If any water does accumulate, the filter(s) will take care of the problem.

What I and others do is not worry about condensation. It's easy enough to take a sample of the bottom of the tank in the Spring to see if there is any water. It can be easily removed with the same pump you probably use to change the lube oil.

 

[Stu Jackson]

When folks mention "The Archives" it might be helpful to suggest a search term. I used "winter fuel" each all words, none for boat category.

Here's one post that came up, you might want to read the whole topic: http://forums.catalina.sailboatowners.com/showthread.php?p=853562&highlight=winter fuel

 

[Tim R.]

I never topped them off for 5 years. Usually left about 10 gallons in a 40 gallon tank. In the spring I would empty the tank for cleaning and never found any traces of water or bugs. You want clean fuel then you need to buy good fuel and keep it in a clean tank.

Never used any additives in those 5 years and never had a fuel problem with the engine.

 

[nauticalrich]

It was recomended to fill the tank and treat with bioblock to keep growth down.

I had a mess in my tank for the first time a week ago. The engined ran out of fuel due to a block fuel shut off valve on the tank. Really weird, the groco filter was actually clean but the lift pump was a mess.
I pumped the fuel out and replaced it with new. Also added the bioblock, new bottle, and filled the tank.

 

[Gunni]

Yes, you top them up to keep the exchange of air (via the vent) to a minimum. It also gives you the opportunity to add/mix stabilizers and dispersants. The air carries moisture, depending on atmospheric conditions, the cold tank walls condense it into your tank. Yanmar recommends FPPF diesel additives, Marine Formula disperses water, stabilizes fuel, and boosts Cetane. I used to work in the emer. generator and bulk fuel business and those folks store fuel for years, many years. We would keep the fuel stabilized, test yearly for cetane, and religiously draw off any bottom water. There are emergency generator fuel tanks with 20 year old diesel in them.

Don, bulk storage doesn't keep water on their tank bottoms, the water accumulates bio waste from bacteria that is corrosive. In fact there is a whole industry devoted to extracting the stuff. The water accumulates in many ways but largely because those big Above Ground tanks have large vented air spaces above the fuel - full of damp air and surrounded by cold (sweaty) steel. Water is nearly unavoidable for those guys, for boaters, we can keep the tank full, and the fuel stabilized. If you use your fuel across two years and treat with FPPF, you will be fine.

If you have water in your tank bottom, siphon it out. In fact drawing off your tank bottoms every year would be a good idea.

 

[Maine Sail]

I usually empty my tank or it's 1/4 or less full. Never once had a water issue. This year it will be under a 1/4 tank or so when she comes out in Nov.. While condensation can, in theory, happen it can't happen to an empty tank and I have not found it to actually happen to a point there there is any physical water in our tanks when minimally full..

 

[RichH]

Simple answer: if you dont want 'condensation' in your tank, then empty the tank!!!!!!!! If 'tank condensation' was valid then the world wouldnt have to dig water wells; just put out empty tanks and they would 'magically' fill with water ..... and you (should) know that isnt true.

Still a doubter .... Take a measured and weighed amount of 'fresh' oil, oil is dehydrated as it leaves the refinery due to the high 'cracking' or distillation process temperatures, and put it in an open container, even a tank that has a vent .... then measure the weight at a later time ---- the increase in weight as the WATER in the atmosphere transfers and goes into 'solution' INTO to the oil by the laws of *chemical equilibrium* .... and No 'condensation involved'.

But but but what about the 'condensation' that everyone is paranoid about? .... Well, when the oil in the tank fully 'saturates' with water from the atmosphere the mixture provides the water for which to 'condensate' on the tank walls when there are thermal differences. In other words, when the oil becomes FULLY SATURATED with water because its in contact with the wet/moist atmosphere (via the tank vent), then there is an ample supply of water to condense on the tank walls ..... but the oil has to become fully saturated to do this before ANY condensation appears. If NO oil, then the oil cant become saturated with water, can it?

If you dont want the oil to become saturated with water in the tank, take the oil out and take it home to burn in your home oil burner.
Filling the tank will only provide MORE mass of oil for the water to 'equilibrate' with ... as long as the tank is open to atmosphere the water in the atmosphere WILL enter the oil until the mixture is fully SATURATED. Water SATURATED oil will condense on the tank walls, condensation is a SIGN that the oil is FULLY saturated with WATER ... and its too damn late to prevent the water 'uptake' into the oil. An EMPTY tank cannot uptake water because there is NO oil into which the water can 'equilibrate'.

Empty the tank when long term storing the boat if you dont want to exceed the 'storage life' (usually just a few months) and to prevent biologic growth.

Secondly the typical 'growth' you find in diesel oil is a common fungus .... 'kerosene fungus' (typical = Cladosporium Resinae or similar RESIN FORMING species ) ..... which uses the oil as a nutrient source and its products of metabolism plus 'dead fungal cells' is the thick black 'deposition' (asphaltic, etc. RESINS from the fungals 'eating' the oil!!!) that accumulates on the tank walls. There is enough 'molecular' water in atmosphere exposed oil to provide all the proper amount of water for such metabolism .... and no need for there to be a stratified amount of water that has 'dropped out' of solution at the bottom of the tank as 'free' water, the water is either emulsified or is in molecular form between the oil molecules because of the *chemical equilibrium' by the 'law of partial (vapor) pressures'.

Empty the tank. Empty tanks dont magically 'uptake' water. Empty tanks dont have enough oil to FEED the fungals and other biologics. Why store oil in an OPEN container only to have it become saturated with water, grow numerable species of fungals, etc. that deposit resins on the tank walls, and provide some bacteria etc. the nutrients for growth in the water that is stratified 'under' the oil? Too cold to feed fungals and bacteria .... The polar regions have a LOT of fungals and bacteria growing under the ice.

EMPTY THE TANK !!!!!!! Leave behind the myths and mysticisms about tank 'condensation'.

Note/Caution: DO NOT block off the vent of a normal fuel oil tank to prevent its natural aspiration of air/water vapor, etc. .... or it will/can COLLAPSE the tank when/if internal pressure becomes a significant vacuum --- dont IMPLODE the tank by clsing a vent valve!!!!!!!! Of course if you want to spend mega-bucks for a full vacuum rated tank then of course closing the vent valve is the easiest way to SAVE and STORE the oil to prevent water and biological spores, etc. from entering .... for long term storage.

 

[Benny17441]

Not surprisingly folks in Maine do not seem to have a problem with condensation. It is physically impossible for cold air to hold much humidity and the temperature changes in the low scale of the thermometer are not conducive to produce it.

 

[MrUnix]

What hasn't been mentioned here is what the fuel tank is made of. If the tank is steel, then it is generally advisable to keep it topped off to prevent rust from forming inside the tank. I have not experienced this on any boats I have owned (since most used aluminum tanks), but have experienced it in fuel tanks on motorcycles and diesel tractors.

Cheers,
Brad

 

[Jimm]

Is it really necessary to top up the diesel fuel tanks when we put our boat away for the winter?

I was going to just add some fuel conditioner and leave them 1/4 full.

Comments?

YES, why take a chance - I failed to do so one year and wound up with 3gals of water (from snow/ice melt) in the fuel tank...........fuel fill cap was not sufficiently tight. Am expensive lessson.

 

[Maine Sail]

Not surprisingly folks in Maine do not seem to have a problem with condensation. It is physically impossible for cold air to hold much humidity and the temperature changes in the low scale of the thermometer are not conducive to produce it.

Interestingly enough we regularly see humidity levels over 40% in winter temps, sometimes over 50% and on warmer days we can see summertime humidity levels. When the temps pop above 32f we can have spikes to 80%+ humidity.. Our temps can sometimes fluctuate up to +/- 40-50f in the same day.. Our conditions are pretty ripe for "condensation".. We have a big ocean that never freezes and keeps humidity near the coast, and boat yards, much higher than in-land just a bit.. Also when the sun hits the dark colored hulls internal temps on the boats can vary by over 30f in an hour or two and can vary by upwards of 50f from overnight temps.. While we do occasionally dip into the low 20's on the hygrometer it is pretty rare unless well below zero for a while.. Temp this morning was 39f and the hygrometer for out doors reading 75%...

I choose to empty my tank or darn close and have never once had any visible or pumpable water in the tank.. Our fuel polishing pick up tube is about 1/8" from the bottom of the tank in the lowest spot, a vee..

 

[CarlN]

Another reason to not top up the tank anymore is that diesel fuel is not as stable as it used to be - at least in the US. It's been reformulated for environmental reasons. Some also has biofuel (sometimes marked sometimes not). Better to leave the tank empty and fill with fresh fuel in the spring (make sure the marina has gotten a new fuel shipment)

I also have a recirculating polishing system like Main Sail. I run it a few times a winter when I visit the boat to get rid of any developing troubles. I also add a bit of Killem biocide each time.

Carl

 

[RichH]

Not to belabor the issue but the ABSOLUTE humidity at 32°F and 100°F isnt 'all that different' and the 'Saturation' of the oil by atmospheric water will still occur, albiet at a slower rate but none-the-less will eventually go to full saturation (depending on the temperature).

Only when the temperature reaches approx. -40° is air considered 'dry' and in industry we 'pad' or blanket oils with -100 dewpoint (considered 'bone dry') air to affect dehydration of the oil; anything ABOVE -40° will saturate the oil with atmospheric water ... and temperature only affects the RATE of saturation.
The important thing here is if the oil is in contact (through a vent, etc.) with atmospheric air it WILL become saturated with water.

http://www.engineeringtoolbox.com/water-vapor-saturation-pressure-air-d_689.html

 

[alexco38]

leave it empty

I am align with Mainesail. I rather ran it as empty as possible (less than 1/4), add diesel treatment before winter. Next spring I'll have fresh fuel.

Also, I have a strainer filled with blue air dryer beads in the vent line. and an on-board electrical fuel filter. See picture.

 

[alexco38]

BTW you can get air dryer beads from air power tools shop. They use blue beads which is re-chargeable in the oven. When it turn pink, just dry it again in the oven. Takes 10 minutes.

 

[Bill Roosa]

I've done it both ways and 1/2 full too. Don't use additives and have never had a problem with water. We do go through about two tanks in a season so it does not sit there for years on end either.

 

[alexco38]

"I typically fill up my tank for winter anyway, and I always drain off a few table spoons of watery crud from my filter a couple of times per season. I can't identify the source of this water, but a full tank over winter didn't prevent it."

Minor crack on the o-ring at the fuel filler cap ;-)