Winterizing fuel tank

[Tim22]

The common practice seems to be to top up the fuel tank at the end of the year to prevent condensation during the winter. My boat has a 25 gallon fuel tank and this season I used about 8 gallons. At that rate it would take 4 years to use all the diesel which is plenty of time for it to go bad and this does not account for topping it up each fall.

I see that Maine suggests draining the tank at the end of the season and starting with fresh diesel in the spring. This sounds like a good solution to my situation and I am wondering what other people's experience is with this. I have followed Maine's advice on many occasions and must admit that he has never steered me wrong.

Thanks for your thoughts
Tim

 

[njlarry]

Maine Sail has done a great piece on the myth of fuel tank condensation: http://www.marinehowto.com
With only 8 gallons used a year I would consider keeping the tank at 16 gallons and using a bio-cide...or moving to place with a longer season. I add a bio-cide to what ever is in the tank in the fall ( near fill but not necessarily topped up) and add fresh fuel to fill it in the spring. Not sure that that is factory spec but it makes some sense to me.
I'm sure you already change your fuel filters regularly.

 

[dziedzicmj]

I am in a similar boat as you (and the same place). I use even less fuel (i think that this year it was just 20 l (5 gal)) - after all, this is a sailboat.
I add a stabillant and bio-cide in the fall (you have to add some fuel with them in order to mix them up) and add new fuel in the spring.
So far, so good. I have this boat with a diesel engine for 3 years and it is working fine. I change fuel filters regularly (fall), even though, I am not sure if it makes sense after they filtered only 20 l of fuel (actually, substantially more, because there is much more fuel going through the filter than is used in the engine) or had only 10 h of running time.

 

[Maine Sail]

Maine Sail has done a great piece on the myth of fuel tank condensation: http://www.marinehowto.com
With only 8 gallons used a year I would consider keeping the tank at 16 gallons and using a bio-cide...or moving to place with a longer season. I add a bio-cide to what ever is in the tank in the fall ( near fill but not necessarily topped up) and add fresh fuel to fill it in the spring. Not sure that that is factory spec but it makes some sense to me.
I'm sure you already change your fuel filters regularly.

Thanks for reminding me! After seeing your post it jogged my memory I just checked it a few minutes ago, with the tissue paper trick, and the interior as still 100% bone dry...

 

[Rich Stidger]

I used to fill up at the end of the season to supposedly avoid condensation. I stopped doing that for four reasons. First, I found that I had no significant condensation, meaning that in the Spring after running the engine and using most of the previous year's fuel, I had no water to drain off in my filter. Second, I think it is better to use the old fuel first thing in the Spring and then fill with fresh fuel for the bulk of the season. Third, I once topped off my tank and had the fuel expand and overflow out of the vent and soak my canvas winter cover- it was a real pain to clean. Fourth, and lastly, I found that the marinas near me jacked their price right before the end of the season, presumably to get more money from those topping off.

What I do is to add a "shock" amount of biocide in the fall and then again in the Spring. Also in the Fall I add a "storage" dose of Power Service Diesel conditioner.

 

[Maine Sail]

Third, I once topped off my tank and had the fuel expand and overflow out of the vent and soak my canvas winter cover- it was a real pain to clean.

The entire Brewer's chain of boatyards disallows storing your boats fuel tanks at any more than 3/4 full for this very reason...

"Yard Rules:
11. Fuel tanks shall not be topped off more than ¾ full prior to winter storage, as spring temperatures may cause expansion and seepage from vents. The Owner is liable for any fuel spill or associated clean up expenses or fines incurred in the event of a fuel spill, whether on land or in the water."

 

[Rich Stidger]

Interesting Brewer's rules. My yard (I just checked) has no such rule. I did not realize that the expansion of fuel would be as much as it was. Live and learn.

 

[Tim22]

My main reason for draining the tank in the fall is that it gives me a chance to clean it out once a year. Also gives me new diesel at the beginning of the next season - no biocides additives. I can give the removed fuel, which is still good, to one of the club members for use in farm machinery. Seems to me everyone wins.

Tim

 

[JamesG161]

Maine Sail has done a great piece on the myth of fuel tank condensation: http://www.marinehowto.com
With only 8 gallons used a year I would consider keeping the tank at 16 gallons and using a bio-cide...or moving to place with a longer season. I add a bio-cide to what ever is in the tank in the fall ( near fill but not necessarily topped up) and add fresh fuel to fill it in the spring. Not sure that that is factory spec but it makes some sense to me.
I'm sure you already change your fuel filters regularly.

I was happy to see that link. The addition by John Churchill, in that link, uses what he called physics to bust the Myth of significant fuel tank calculations. He was spot on his analysis, but he left out solubility of water in diesel. Using his teaspoon of water in the extreme Dew Point cycles, you might try this simple test for yourselves (if you don't believe the science).
Get a quart mason jar and fill half from you marine fuel source. Place the labeled open jar in an "no rain" outdoor area safe from tampering, children, etc. Put a teaspoon of water on top of the diesel and observe to see if it sinks. It won't! The reason is called surface tension. The fuel/water emulsifiers we can add to fuel, breaks the surface tension of water.

Over a long time, the water will be dissolved in cold diesel, but as temperature increases, it evaporates too.
So if you have found significant water in the bottom of your diesel tank then it came from...
1) Many years of accumulation
2) Water in a fuel supplier's tank
3) Bacteria creating/holding the water in your tank
4) Liquid water intrusion through tank vent

The easiest way to protect you engine for NON dissolved water is a good Fuel Filter with a liquid water separator. Run you tank low level in 2' seas will let the fuel filter do its job to polish the last seasons fuel. Also use a good fuel supplier who uses fuel with a biocide. I carry 15% of my fuel tank in safe Jerry cans and 3 spare filters when I do my seasonal fuel polishing.
Jim...

PS: When my boat was delivered, the Captain said the past owner must have been angry, since he left the diesel tank empty and the hold tank full. The boat was delivered in 8' seas thus mixing the crap in the tank effectively (tank was trip filled 2.5 times). I had to change Fuel filters 2 times and the filter is clean and no visible water ( I drain a bit of it anyway).

 

[JamesG161]

Interesting Brewer's rules. My yard (I just checked) has no such rule. I did not realize that the expansion of fuel would be as much as it was. Live and learn.

I just found this science correct diesel fuel expansion coefficient info.

The clearest answer I've heard to date is that the coefficient is 0.00046 per degree Fahrenheit. That is to say that for every degree rise in temperature your volume will go up that amount. The math works like this, say you have a temperature rise from 60 degrees f to 84 f over the course of a day and a tank with 100 gallons of diesel in it. Multiply the coefficient by the number of degrees temp rise (24 x 0.00046=0.01104) then multiply that answer by the total number of gallons you started with to get the number of gallons increase in the tank when the diesel warmed up to 84 degrees (0.01104 x 100=1.104 gal.)
Remember the liquid itself has to rise in temperature and it may take a long time to do but this is a handy way to figure the amount of room to leave in a tank for expansion.

Please note that temperature rise expands the liquid and the tank construction material too.
So if you fill your tank in warm weather with say 70°F diesel, then it won't overflow. I say that because I know most of us want to get our boats out long before 70°F in the spring. But you get the point.
Jim....

 

[Maine Sail]

I just found this science correct diesel fuel expansion coefficient info.



Please note that temperature rise expands the liquid and the tank construction material too.
So if you fill your tank in warm weather with say 70°F diesel, then it won't overflow. I say that because I know most of us want to get our boats out long before 70°F in the spring. But you get the point.
Jim....

However here in Maine we have boats "topping up" for winter today and and it was 29F this morning, hence Brewer's general rules.... I am still trying may hardest to use as much fuel as I can before haul out so I can use a 2 gallon jerry can to empty the rest.... Boats also sit on the hard at slight angles with fuel potentially up against the fuel vent and it does not take a lot for it to expand out if the tank was filled in sub 40F weather.....