"Worth it" to top off diesel for the winter?

[CarolinaCalm]

Good info thanks. I am a 'topper' but my tank is small and easy to fill. I would think that periodically transferring fuel to the empty tank would rinse any condensation from the tank sides into the fuel and then when you transfer fuel out you would be introducing 100% new and possibly moist air,..rise and repeat. I would either top it off or leave the empty tank alone
Just my 2 cents

[a64pilot]

Actually Cotemars pictures are a nearly perfect example of condensation.
Likely a gasoline automobile I assume. The filler neck is much cooler than the oil is and water condenses in the neck, just the source of the water is a by product of burning fuel, reason there is so much water there.
Be similar to if you pumped steam into your fuel tank, if you did that, then of course condensation would be a problem

[Dockhead]

Originally Posted by Dockhead

. .So if you do this 180 times over half a year, you will get 4.338 grams of liquid water in the fuel, assuming none of it evaporates back out.

To put this in context of statements like "I had two gallons of water in my fuel, therefore it is condensing out of the air in the tank" --

If a half-empty 500 liter fuel tank breathes in the maximum amount of air which it can get from a 5C temperature cycle, and every bit of that air is at 100% humidity, and all the water in that air which can condense due to a 5C temperature difference, condenses out (which is impossible, but just suppose) --

And this happens every day for 180 days every year --

Then in one thousand years (1000 years), the water so condensed out will amount to just over one U.S. gallon. That is for anyone who thought I was being hyperbolic when I told someone here that he couldn't get his two gallons of water, from condensation, even in 1000 years of tank "breathing".

But even that is totally impossible because:

1. Relative humidity is rarely 100%, much less 100% of the time.

and

2. Breathing in occurs when it's cool, not when it's warm, so you'll never get any of the warm saturated air you need for condensation through the daily thermal cycle.



In the Middle Ages, it was believed that the Bubonic Plague was caused by bad air, and by a certain alignment of the planets. "Everyone is sick and dying; therefore the air must be bad." The theory was elaborated to explain how the air got bad -- the devil made the sea rise up and expel the "miasma".

Everyone believed it -- because someone else told them. And people are dying, so it's obvious that it's caused by bad air (same logic as "I found two gallons of water in my fuel tank; therefore water definitely condenses in the tank"). Also, "Lothar spent the summer on the mountain, and didn't get sick. Therefore, it's obvious that miasma causes Black Death, because there's no miasma on the mountain."

In this day and age, we have access to better methods of understand things which happen, than this.

[Stu Jackson]

Facts, logic, engineering and reality rarely get in the way of repeated "untruthiness" these days.

Too bad.

Thanks to Dockhead and the few others of you who have used real engineering to explain and debunk this silly urban myth.

[doublewide]

re: biocide and other fuel treatments, Practical Sailor published reviews of several products. You may wish to see which products were recommended based upon testing.

Diesel Biocides Take On Contaminated Boat Fuel - Practical Sailor Print Edition Article
Diesel Additives - Practical Sailor Print Edition Article

[thinwater]

Originally Posted by a64pilot

You will likely never get a manufacturer to recommend an additive unless it's branded by them, reason is they have nothing to gain, and everything to lose.
Why recommend X additive even though you know it works and causes not harm? You gain no profit, manufactures of Y and Z additive will likely squall like stuck pigs, and unknown to you X changes the ingredients and now it doesn't work, and may cause harm, meanwhile your told your customers last year to use it.
Best to tell your customers to use no additive that isn't your brand, and if you offer no additive your stance is use none at all.
You tell them to always top off their tanks, cause it does no harm, and you will have no end of arguments from lots of people who have stories if you don't.

Now I will state that it is my belief that most additives are right up there with fuel line magnets and intake Vornadoes and Teflon oil additives etc., meaning at best they do no harm.

I thought additives were mostly snake oil until I got involved in systematic testing. The real answer is that some are junk, but most are valuable. How can you tell the difference?

Biocides. These are EPA registered as pesticides, and all of the registered ones work very well in testing. Their use is actually required in jet fuel.

Corrosion and gum. Practical Sailor has done bunch of testing. In this case, some are good, some virtually stop corrosion, and a few actually make it worse. Those that stop corrosion also stop gum formation, because most of the gum results from metal ion catalysis.

The answer is that the differences in fuel deterioration rates can be HUGE.
---

As for condensation, it is a fact of life (inspect any large diesel tank and you will see water dripping from the roof--I used to do large tank inspections.The amount, of course, is tiny, but it only takes PPM levels to increase corrosion rates. There does NOT need to be a free layer in the bottom. But rather than worry about it, install a silica gel vent filter. I've been running one of these for 5 years, in combination with an effective additive, and now my system is shiny clean and I only replace filters when they get corroded!

The only difference between these samples was the type of vent filter used (none, silica gel, carbon)



http://sail-delmarva.blogspot.com/20...iesel-and.html

[Celestialsailor]

Originally Posted by Dockhead

Cool, could you share it with us? If yours is right and mine is wrong, I will be very glad to learn something.

Dockhead...it's been covered by others...the temperature changes causing moisture to fall out of suspension in the air into the diesel tank. Less air...less water. I can only assume and speculate (much like Steadyhand likes to do) that you have it made up in your mind that water does not fall into diesel this way.
On other topics you tend to be fixed in your ways. Anchoring comes to mind.
Do what believe in and I'll do the same. But you must see that there is a large percentage here that believes you should top off the tank as I do.

[Celestialsailor]

Originally Posted by valhalla360

So far several people have pointed out the math and science that it is impossible to get any substantial amount of water from condensation.


That goes up against people talking about their grandpappy told them to do it, there's water in the fuel and they have no clue where it came from so it must be condensation, the crankcase is full of water (still not clear how that is relevant to the discussion), they do it to save the little children, etc... but oddly, they never provide any calculations to support their theory, just broad generalities that air contains water and it could condense out.


Please if you are going to claim it happens, please someone provide some calculations to support your position.

...and please feel free to do the same.

[DumnMad]

I think the condensation calcs may miss the point.
As I understand it; In a partly filled tank the diesel absorbs moisture from the air space resulting in a lower water vapour pressure in the tanks. Diffusion caused by vapor pressure differentials drags new moisture into the tank which is also absorbed by the fuel & so on. "Condensation" is a bit of a slang term for this process.
In a full tank there is no air so no diffusion, in an empty tank there is no diesel so no absorption.

[Panope]

Just another testimony to add to the debate.

-Tanks in Boat for 16 years.
-Tanks have NEVER been full.
-Tanks have NEVER been empty.
-Tanks remained motionless for 12 years with the same 1/4 tank of fuel.
-Tanks have an exterior vent that has been open to the atmosphere at all times.

-Boat has never been stored under cover.
-Boat has been heated during manned construction or weekend cruising only.
-Location: Western Washington State (they say it rains a lot here).
-Temp varies between 20 F. and 90 F.

I am religious about taking fuel samples from the extreme bottom of the sumps and I have found a total of 2 or three DROPS of water, on one occasion, in these 16 years. No other debris has been found in the tanks.

Steve

[Dockhead]

Originally Posted by Celestialsailor

Dockhead...it's been covered by others...the temperature changes causing moisture to fall out of suspension in the air into the diesel tank. Less air...less water. I can only assume and speculate (much like Steadyhand likes to do) that you have it made up in your mind that water does not fall into diesel this way.
On other topics you tend to be fixed in your ways. Anchoring comes to mind.
Do what believe in and I'll do the same. But you must see that there is a large percentage here that believes you should top off the tank as I do.

Your words were -- "Sorry...I think my math is just fine" -- we were talking about math, not beliefs.

That you have a belief -- is not in question. And of course you are perfectly entitled to your beliefs. If you are not interested in the actual science and math of the question -- then of course, that is your prerogative.

[Dockhead]

Originally Posted by DumnMad

I think the condensation calcs may miss the point.
As I understand it; In a partly filled tank the diesel absorbs moisture from the air space resulting in a lower water vapour pressure in the tanks. Diffusion caused by vapor pressure differentials drags new moisture into the tank which is also absorbed by the fuel & so on. "Condensation" is a bit of a slang term for this process.
In a full tank there is no air so no diffusion, in an empty tank there is no diesel so no absorption.

That's a completely different mechanism, from what some on here believe in, and has nothing to do with condensation.

What you are saying is that fuel exposed to air absorbs moisture [definitely true], and keeps absorbing it until it starts to precipitate out [don't know], and that vapor pressure differential causes circulation [very doubtful, but it's not essential to your argument, because there will be a little circulation anyway from breathing].

I've never heard this theory before. Have to think about that one.

[ramblinrod]

Originally Posted by stevec195

Although I do leave my tank topped whenever feasible, the more salient issue for condensation is temperature. If you leave a small box heater in the cabin with the engine access open, the fuel is unlikely to get below the dew point of the ambient air. Admittedly, places in the icee tundra will take a little more thought; but if you can keep your fuel in the 10' C range that would go a long way. Here on the gulf coast, it would be more important to boost that value to 15+ since we tend to get very warm moist spring air with corresponding high dew point. My little box fan also has the advantage of keeping condensation in and outside the engine at a minimum.

Note that leaving a portable heating device unattended may violate your marina contract and vessel insurance policy.

[Celestialsailor]

Here's a Youtube talking about water in diesel and how it may get in...

https://www.youtube.com/watch?v=N01DgXEboD4

Here's an article explaining the same...
How does water get into my fuel tank

Another article from Racor explaining water absorption from air heating and cooling in a tank and the importance of topping off...Yes a diesel filter company...
Racor News

Another article of how little temperature change is needed to creat the absorption problem...
Condensation in fuel, & how to solve the problem

One thing to remember in my situation where I found water in my tank was I use my engine a lot here in Mx. The starting, running of the engine acutually heats the diesel up as opposed to a boat that sits. So the temperature differential between the diesel and the water temperature on the keel (integral tank) is high. So a boat that sits a long time not running may not necessary have the same amount I would have. My tank may heat up 4 times a week and then cool.
This I hope sheds a little light on the topic.

[topmast]

That's an extreme situation but it sheds light. Even if the tank sat at even temp all winter ,the outside temp varies and barometric changes daily regardless of temp. To me that means there's a good chance of some vapoured moisture finding it's way down the vent .A quick calcuculation here can figure how long it would take a Bantam rooster to make a hardware store from a brass doorknob . Formulas with decimals and moles have always impressed the crap outa me.