Fuel polishing--dirty diesel fuel tanks

[psneeld]

Sorry didn't mean it to be snarky....just stating what I know and the problem with urban legends in general....hard to disprove as there are more examples that they are true rather than the other way around.

I also didn't say that you started it...you were just passing along what you believed to be true....which is just one more candle on the urban legend cake.

If I wanted to be snarky...you would have a lot more ammo to throw at me....

As far as moving things forward...I gave my experienced opinion...so yes to those that know me or like my posts.

If I was thin skinned, I could say that comment was snarky...but I have thick skin...

 

[Yahoo 1]

If I wanted to be snarky...you would have a lot more ammo to throw at me....

You said. On this point, I trust you.

 

[dhays]

Water from the air in a empty or insufficiently fulfilled closed tank will condense in the inside walls of the tank as a direct consequence to changes of temperature at the outside of the tank, no matter what type of fuel or liquid contained in the tank.

That is what we all have heard and many of us have repeated. Can you provide any actual evidence to support it however?

 

[dhays]

Why are you so snarky ? I am aware that I am only a newbie here, but as far as I know, I don't have to accept your unpleasant comment - not to say misogynous -.

Have you got the impression that your comment has moved things forward and if so how?

Lol, I think there is a problem here with language, idiom, and culture. Believe me, PSneed's comment was NOT meant to be snarky, demeaning, or insulting at all.

Just to be clear, the term "old wive's tale" is a common, if old fashioned US expression to denote an idea that has long been repeated as truth, even if it lacks sufficient evidence of fact. I can certainly see how the comment could be misinterpreted from your standpoint.

 

[dhays]

I did read one author who felt that any fuel, diesel included, that is exposed to air will eventually reach its water saturation point. Since all our tanks have vents, this would include all of them. If the fuel because completely saturated, it is possible that some water could separate, falling to the bottom. Then the fuel would add water from the air to maintain that saturation. In this way, fuel stored for a sufficiently long time could accumulate a fair amount of water in the tank.

This would argue that the best course would be to keep as little fuel as possible in the tank for long term storage.

Even though CMS's test was with an empty tank, it would seem that if the argument is that you get less condensation with a full tank than a 3/4 full tank, and even more with a 1/2 full tank, that you would get maximal condensation with an empty tank as that will have the most tank surface area to provide a condensing surface. So far, CMS's tanks have been dry.

 

[Steve DAntonio]

Steve D and FF, I appreciate the input, but I think most of us either buy a previously owned boat or a production boat. It's not hard to imagine the ideal fuel tank setup but we don't usually get to specify any such requirements, we take what we get and do the best we can.

In my case, there are no inspection ports so pretty much the only way to draw fuel/water from the absolute bottom of the tanks would be through the fuel fill (which is not straight but has an "S shaped hose) with a flexible hose with a weight on the bottom.

The bottom of the tank is flat so there's no guarantee of getting all the water out even by doing that.

I try to keep my tanks filled to minimize condensation and I try to buy fuel at reputable places. I use Stanadyne treatment. So far, it has worked.

Wes:

Understood, there are few perfect tank scenarios. Inspection ports can be added, and while not easy per se, it's straightforward and decidedly not high tech.

I've added stripper tubes to many tanks, without wells, that's not a pre-requisite. Indeed, no guarantee of getting all the out water when the tank bottom is flat, however, if the stripper pick up is lower than the engine pick up, your chances are better than nothing.

In my experience, and testing, the condensation concern is overrated. Virginia has to be one of the top regions for generation of condensation, it's not uncommon to have a 50F temperature shift in 24 hours, and 70F isn't unheard of over a few days. When I ran a boat yard, I carried out an experiment, peering into an empty aluminum fuel tank all winter long, once every few days. I never witnessed a drop of condensation form. That's not to say it doesn't happen, I've taken many photographs of condensation having formed on the underside of fuel fill caps, however, these, being on deck, are subject to more rapid cooling, and thus more effectively promote the formation of condensation.

Of course there's no harm in keeping a tank mostly full; I suspect much of the water I find in tanks comes in with the fuel, through vents as spray, and through faulty O rings in deck fills.

 

[FF]

Just reading the spec sheet for diesel delivered by pipeline will show where some water comes from.

Over time enough can drop out of suspension to allow those bugs to live.

On our 90/90 we use a" baja" filter (made by Rybovitch) and on the AICW have caught as much as a half cup of water in fueling just 20Gallons!

I can only imagine what gets aboard taking 150G in the Uniflite.

The concept that what you fill the tank with is clean is very overrated

 

[AusCan]

It seems that fuel issues are one of the biggest cause of problem on a boat. It is worth getting a decent fuel system installed.

I bit the bullet and replaced my corroded, dirty, poorly designed fuel boxes. Now, if I get any water in the tank, it is easy to see in the bottom of my sight glass. The sight glass is tied into the lowest part of the tank, along with a drain point. It is nice to be sure that your tanks are clean when venturing out in rough water.

I find that my engine only uses 20% of the fuel drawn from the tanks. The other 80% is filtered then returned to the tanks. In effect, the fuel will be filtered an average of 5 times before being used in the engine. No polishing required.

And I agree - check and clean/change your fuel filler cap o-rings. A little bit of sand gets in them and chews them up. Then any water on deck slowly gets wicked in to your tank. Thats the most likely place water is coming from; or from your fuel supplier, not condensation.

 

[sdowney717]

My fuel deck fills made by Perko from 1970 sit above the deck about an inch.
They are bronze pipe with a chromed bronze screw on cap. The cap has a stamped bronze link chain that is attached to the bronzed fill pipe. Threads are NPT.

I added a gasket inside the cap, don't know if it used to have one. But certainly no rain-dirt-sand could ever get in, maybe an ocean wave?, good reason for putting in a gasket.
Fill is up close to cabin side, so not a tripping hazard. So I have one for each tank. And I got another one, same thing off a crushed dumpster boat in case I ever put in a holding tank. My old marina, lots of older boats sent there to be demolished, so I was able to get lots of little freebies.

My fresh water fill is a standard type chromed bronze flush to the deck fill. Even that sticks up 1/4 inch off the deck. The rubber oring is long gone. That sits in a place near the door and never gets much rain.

 

[sunchaser]

It seems that fuel issues are one of the biggest cause of problem on a boat.

Now this is an old wives tail, but I've not purchased diesel where bad fuel is common. I avoid those places or shore bases delivery trucks. Like anchors, every boater has a filter and fuel tank and a possibly unique situation. Thus the wrong thought we are all suffering bad fuel equally.

 

[what_barnacles]

Why are you so snarky ? I am aware that I am only a newbie here, but as far as I know, I don't have to accept your unpleasant comment - not to say misogynous -.


newbies, they always come out blazing.

 

[BandB]

Just reading the spec sheet for diesel delivered by pipeline will show where some water comes from.

Over time enough can drop out of suspension to allow those bugs to live.

On our 90/90 we use a" baja" filter (made by Rybovitch) and on the AICW have caught as much as a half cup of water in fueling just 20Gallons!

I can only imagine what gets aboard taking 150G in the Uniflite.

The concept that what you fill the tank with is clean is very overrated

It is for this reason that we test the fuel before filling. 99% of the time we've found no problem. The other two times, we've said "no thanks" and fueled elsewhere. That's only twice in four years but those two times could have resulted in problems. Would our filters and/or polishing system have prevented a problem? Probably. However, best to not let the contaminated fuel ever into the tank.

 

[O C Diver]

It is for this reason that we test the fuel before filling.

Just curios what your test is and how much fuel you test?

What's in the nozzle and the pipe coming down the dock may have no resemblance to what was dropped by the tank truck an hour before you pulled up to the fuel dock. Even if you're buying off the fuel truck, what's in the 100' of hose on the truck may have no resemblance to what they loaded into the truck before coming to your boat.

Ted

 

[rwidman]

My boat's owner's manual suggests keeping the fuel tanks as close to full as practical to reduce the chance of condensation. Many other sources do as well. It's far from an "old wives' tale".

Now I realize that many people don't believe that condensation will form in a boat's partially full fuel tank, but many others do. There will be air moving in and out of the tank through the vent and as fuel is used up by the engine. If that air is moist and at a higher temperature than the fuel or the tank walls, my high school physics education and personal experience tell me that it can happen. Maybe not in Arizona, but certainly in warm, humid climates. Keeping the tank full of fuel minimizes the amount of air movement and the temperature change.

It is a free country so you can believe whatever seems believable. One person can do a study and come up with a set of results while a different person does a similar study and comes up with a different set of results. Which one is correct?

 

[BandB]

Just curios what your test is and how much fuel you test?

What's in the nozzle and the pipe coming down the dock may have no resemblance to what was dropped by the tank truck an hour before you pulled up to the fuel dock. Even if you're buying off the fuel truck, what's in the 100' of hose on the truck may have no resemblance to what they loaded into the truck before coming to your boat.

Ted

You're correct in what you're saying. However, what those with far more experience than I have said is that the majority of the time the problems are immediately apparent. Now, we have good filtration and we have fuel polishing on one boat. We test a very very small sample. If using two hoses, we will test a small sample from each. The main thing we're testing for is water and it's generally immediately visible. The risk is that there is contamination in the tank that isn't being pumped yet, but will be. However, most of the time it's going to show up immediately.

One time we felt bad because the owner of the marina was present and he was a very nice man. We asked if he'd checked his tank recently. He was embarrassed that he hadn't for a week or so and so we went with him to check. He normally had about 3" of water in the bottom but when he checked with us he had closer to a foot, which meant enough to reach his fuel pickup. He shut down his pumps and called the distributor right then.

We use to do a lot of winter boating on the lake in NC. Not many boaters around and some of the marinas sold very little fuel. They also kept their tanks low as they didn't want to buy fuel until spring. There was a campground that regularly had water in their fuel. Most boats would leave there, start sputtering, barely get to the marina and boatyard. 90% of the time they could then use an additive and get it to burn and within a few minutes while running at the dock, their engine was running well again. A few had to have their tanks emptied.

Most of the places most of us cruise are really very low risk. However, the most serious problems are easily detectable visually.

 

[dhays]

It is a free country so you can believe whatever seems believable. One person can do a study and come up with a set of results while a different person does a similar study and comes up with a different set of results. Which one is correct?

Just because something is repeated often because "it makes sense" doesn't make it true. I've seen this a lot professionally where we find we have been telling patients things for years because we all think it makes sense only to find that after the research has been done it simply wasn't true.

The correct study, to answer that rhetorical question, is the one that is repeatable and verifiable. So, if you have some evidence that water has appeared in a partially empty fuel tank demonstrably due to condensation, then I would be interested in seeing it.

 

[rwidman]

Just because something is repeated often because "it makes sense" doesn't make it true. I've seen this a lot professionally where we find we have been telling patients things for years because we all think it makes sense only to find that after the research has been done it simply wasn't true.

The correct study, to answer that rhetorical question, is the one that is repeatable and verifiable. So, if you have some evidence that water has appeared in a partially empty fuel tank demonstrably due to condensation, then I would be interested in seeing it.

As I posted above, "It is a free country so you can believe whatever seems believable."

Back in the day when lawnmower fuel tanks were made of metal, I saw many of them put away for the winter with a half a tank of gasoline and in the spring they were full. Half gas, half water. And wouldn't start. I was the neighborhood "fix it guy".

Don't bother to reply that you're not supposed to do this or that we're talking gasoline here, it doesn't matter. And don't bother to ask me for evidence because you're not going to believe it anyway.

Again, "It is a free country so you can believe whatever seems believable."

You're going to have to fill that tank anyway, why not when you come back from a cruise, rather than before you leave again? That way, you don't have to be concerned about possible condensation. And, you cn just head out without delay.

 

[psneeld]

The Myth of Condensation in Fuel Tanks

by David Pascoe

http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

Another mathematical calculation of condensation in tanks...one of many I have read disproving the old myth....

No one is saying condensation doesn't form...just enough to that a decent filter can handle it all season long....

 

[Yahoo 1]

That is what we all have heard and many of us have repeated. Can you provide any actual evidence to support it however?

Yes Your Honor, I have some, even if I have no illusions to be heard.

- Photos 1 & 2 : The recommendations from the French Ministry of Defense to the French Navy for motor fuel safety standards which an official copy is attached below :
Gazole de Navigation - Eau.
Il y a en effet deux causes distinctes. La condensation de vapeur d'eau dans les réservoirs s'effectue à l'occasion d'un refroidissement.
Diesel navigation fuel - Water.
Indeed there are two different causes. Water is condensing in the fuel tanks when temperature is dropping. etc..

- Pictures 3 & 4 : Caterpillar 3116 (my engines) / 3126 Marine engines maintenance Manual :
Fill the fuel tank after operating the engine inorder to drive out moist air. This will help prevent condensation. Do not fill the tank to the top. The fuel expands as the fuel gets warm. The tank may overflow.

- Pictures 5 & 6 : Caterpillar C18 Marine engine maintenance Manual :
Idem : Fill the fuel tank after operating the engine inorder to drive out moist air. This will help prevent condensation. Do not fill the tank to the top. The fuel expands as the fuel gets warm. The tank may overflow.

- Pictures 7 & 8 : From Caterpillar Inc: Headline "Fuel For Thought" which stated :
"Water Contamination.
Water can get into your fuel if it’s mishandled by your fuel supplier. Most often, however, water gets into fuel tanks by condensation from the atmosphere. As the tank empties, air enters the tank. Water condenses on the walls and runs down the sides. The water never evaporates because it's heavier than fuel and goes to the bottom of the tank. After this process is repeated several times you may have a significant amount of water in the bottom of your tank."

- Picture 9 :
Recommendations from BP (formerly British Petroleum) / BP.com.
Tanks should be kept full to reduce the space for water to condense, maintaining tanks half full increases the water build up and promotes corrosion in the top half of the tank. Most water will come from condensation as the tank breathes, the rate at which water collects will depend on local climate and will be higher in hot humid coastal areas.

Even if I am not a specialist in "condensation in hundreds of boat and empty fuel tanks" let me state my own opinion about this. A part of the water found in fuel tank comes from condensation which precipitate on the inside walls of the tanks when temperature is dropping. It is not difficult to understand that all this water will run down less or more slowly. Therefore the walls will dry until the next time this process (condensation from the atmosphere) will happen again, and so forth.

When opening the tanks for a control, it is not surprising to me that the walls could be dry, for the reason there is a chance that the precipitated water would be already down at the bottom of the tank which does not require much time.

Anyway condensation is far more insidious, it varies from weather conditions, from a place to another, from region to region. Thus, not many conclusions can be drawn from that but one : the principle of precaution, which would require that the tanks would be filled up (or to empty the thanks) to allow risks of water from condensation. Since still I am not a specialist in "empty fuel tanks", it seems to me, however, that the tanks of our boats are a lot easier to fill up than to empty... Therefore I keep mine full.

Let us be clear on that : Of course I am very well aware that "free water entry from fuel fills, vents, marina tanks " is a huge issue, Psneel did not re-invent the wheel about that (common & old fashioned French expression to qualify an already very well know idea). I never believed to be right, I was just drawing attention on the logic to keep tanks filled up because the issue of water from condensation is not to be taken lightly. I don't care to be right or wrong, I was here to learn lot of things I don't know and to share my little experience. I just thought that everyone should feel free to participate according to his ideas, without fear of derision or sarcasm which are not very conclusive arguments. Now, I give up with the thread.

 

[O C Diver]

You're correct in what you're saying. However, what those with far more experience than I have said is that the majority of the time the problems are immediately apparent. Now, we have good filtration and we have fuel polishing on one boat. We test a very very small sample. If using two hoses, we will test a small sample from each. The main thing we're testing for is water and it's generally immediately visible. The risk is that there is contamination in the tank that isn't being pumped yet, but will be. However, most of the time it's going to show up immediately.

One time we felt bad because the owner of the marina was present and he was a very nice man. We asked if he'd checked his tank recently. He was embarrassed that he hadn't for a week or so and so we went with him to check. He normally had about 3" of water in the bottom but when he checked with us he had closer to a foot, which meant enough to reach his fuel pickup. He shut down his pumps and called the distributor right then.

We use to do a lot of winter boating on the lake in NC. Not many boaters around and some of the marinas sold very little fuel. They also kept their tanks low as they didn't want to buy fuel until spring. There was a campground that regularly had water in their fuel. Most boats would leave there, start sputtering, barely get to the marina and boatyard. 90% of the time they could then use an additive and get it to burn and within a few minutes while running at the dock, their engine was running well again. A few had to have their tanks emptied.

Most of the places most of us cruise are really very low risk. However, the most serious problems are easily detectable visually.

It's probably me, but it seems unclear whether you're referring to buying modest quantities of gasoline or hundreds (maybe thousands) of gallons of diesel.

As a side note, for the 7 or 8 years I owned and operated gasoline powered charter boats, I never bought fuel at marinas due to the increase risk of water content.

Ted

 

[BandB]

It's probably me, but it seems unclear whether you're referring to buying modest quantities of gasoline or hundreds (maybe thousands) of gallons of diesel.

As a side note, for the 7 or 8 years I owned and operated gasoline powered charter boats, I never bought fuel at marinas due to the increase risk of water content.

Ted

In NC I was referring to moderate quantities of gasoline. In recent years I'm referring to hundreds and thousands of gallons of diesel.

On the lake we lived on the only choice for gas was marinas. Our boat did only hold about 110 gallons there though. I'd been there for a long time so I knew which marinas to trust and which not, but a lot of people sure had issues.

The only two times we've seen a problem in coastal or offshore cruising were at locations far apart and very different, one in the US, one outside. The one in the US was water only, the other one was water and all sorts of other stuff. You just looked at it and wondered what in the world was in it.

 

[dhays]

Yes Your Honor, I have some, even if I have no illusions to be heard.
...
I don't care to be right or wrong, I was here to learn lot of things I don't know and to share my little experience. I just thought that everyone should feel free to participate according to his ideas, without fear of derision or sarcasm which are not very conclusive arguments. Now, I give up with the thread.

Pilou, please forgive me if I gave you the impression that I would not listen to your ideas. I also certainly didn't mean to deride or be sarcastic and I am pretty sure that others weren't as well.

 

[sunchaser]

Yes Your Honor, I have some, even if I have no illusions to be heard.

I just thought that everyone should feel free to participate according to his ideas, without fear of derision or sarcasm which are not very conclusive arguments. Now, I give up with the thread.

Good job Pilou. Your position has been largely supported for decades if not maybe a century now by fuel farm operators and large tankage operations (ships and off road equipment). Equipment such as coalescers, filter media, drain traps/sumps and centrifuges are some of the tools used to deal with moisture issues.

In this day and age of "internet intelligence" doubters of things like to holler out "provide a link" as if this will provide proof positive on any one subject and position. I ignore much of this as the links tend to be an advertising or marketing statement for product X,Y or Z

Now if only Cat would provide a written protocol that is really foolproof for how to service a marine after cooler ----- To me this is far more relevant than moisture absorbed by diesel fuel during the year which has never caused me a worry whereas after coolers are a PITA.

 

[rwidman]

Yes Your Honor, I have some, even if I have no illusions to be heard.

- Photos 1 & 2 : .....................

Thank You!

 

[Xsbank]

1 gm water = 1 ml
8 gm water per cu meter of air at 8 degrees
28 gm water in air at 30 degrees
1 cu meter = 1000 litres
1000 litres = 264 US gallons

Call me a skeptic but I really don't believe that condensation is a significant issue with fuel tanks despite all of that good industry evidence to the contrary!

A 1000 litre fuel tank is 1 cu meter. At 8 degrees C, 1 cu meter of air can hold 8 gm of water. A gram of water is 1 ml, which is pretty small. However, the tank will usually not be empty so let's fill our tank half full (132 US gallons). That means we have room for 1/2 cu meter of air or 4 ml of water.

If we raise the temperature to 30 degrees, the air can hold 28 ml of water or in our case, half of that - 14 ml. That means, all things being equal (as the air cools it gets more dense so some air will enter the tank through the vent but I'm making no effort to measure it) the air can now only hold the lower amount of air so 10 ml of water must condense out. The amount of air moving in and out of the tank is very small due to "breathing" so it's reasonable to assume there is only very tiny amounts of "fresh" air with its moisture content, being introduced to the tank and this model ignores that some of the condensate will be reabsorbed when the air temperature rises. If some of the water sinks below the fuel level it will not be absorbed by the air when it reheats so the warm air is under-saturated which would tend to draw some of the water out of the fuel again.

10 ml is 0.33 ounces! That tiny amount of water in 500 litres (132 US gallons) of fuel is, in my opinion, insignificant.

I love to contradict the French Navy! (Hi Pilou!)

 

[Northern Spy]

A 688 class submarine has a tank called the normal fuel oil (NFO) tank. It is where the diesel fuel is stored. It also serves as shielding from the reactor. When the diesel is removed and transferred to the day tank, water is added to keep it full. Go figure.

FWIW, my boat does have its fuel pick ups at the bottom. Once I had a leak in my filler which put a considerable amount of water (SAY 4 gallons) in my starboard tank. I pumped the water out with a barrel pump into two containers. I used my racor to stop the remaining few ounces. Changed filters three times. Water settled out in the containers after a week or so. Skimmed the fuel off of the containers and ran it through my truck. Pumped out some of the water. Disposed of the rest at a recycling depot. A pain, but not a big deal. That was years ago. No problems since. Borescope inspection shows clean aluminum tanks every time.

So just a data point. But I really tend to think that people in the South East US have some really skanky fuel.

 

[BandB]

So just a data point. But I really tend to think that people in the South East US have some really skanky fuel.

And you think that, why?

 

[O C Diver]

That was years ago. No problems since. Borescope inspection shows clean aluminum tanks every time.

So just a data point. But I really tend to think that people in the South East US have some really skanky fuel.

Clearly you don't live in an area with a great enough high and low temperature deferential. Probably not enough humidity in the PNW for it to occur either.

Ted

 

[Northern Spy]

I say it because it just isn't much of a problem outside of the SE US. Not going to go digging into the PADD transfers from area to area, but it appears that SE distilate fuel comes from PADD 3 refineries. Very rarely do we hear of issues in the West or North East, that's all. More than 75% of fuel now transfers between independents. The West and Canada has only a handful of refineries. The refineries and distribution networks in Canada and Australia are still mainly in the hands of largish oil companies. Not sure about Europe. I work for a fairly large integrated oil company. If there is an out of specification reading in the system, it is reported in an incident reporting system. If it makes it to a customer, if often makes the newspaper. It just doesn't happen often.

Most of the fuel polishing companies in the West, seem to be oriented towards the bulk terminals, not the end user.

Just an casual observation, that's all. Could be way off base and it might just be a volumetric skewing of the problem. Or maybe it is completely a regional weather phenomena; if so, then the tankage at bulk plants and terminals might be the problem.

Check your weather data.
The highest average relative humidity in the US is the PNW.

 

[BandB]

Northern Spy

The fuel issues I've seen in the US haven't been refinery issues. The ones on the lake were all marina issues. The one I saw on the coast was a single delivery truck issue. Outside the US, I've never had an idea what the source of the problem was.