Fuel additive needed?

[sailsail]

We discovered about a month after haulout that the marina did not fill the fuel tank when they took it over for haulout. We had requested they fill it.....we have always filled it other years. But they said diesel fuel tanks did not need to be filled. I never heard this before, but as it was after the fact, the tank sat 1/3 filled all winter. We did add Biofor.
Do we need to add something before starting the engine? I have read somethings about moisture condensation and am concerned.

 

[Don S/V ILLusion]

Another common myth disproven by various studies. Condensation in the tank is possible but only in trivial amount. If you want to verify the quality of your fuel, remove the gauge sender or return line and suck a small quantify from the bottom by inserting a ubiquitous oil change pump tube to the tank bottom, let it settle and you can easily see if any water is present.

If water is present, it is likely a result of rain water entering via the fill cap or vent, neither of which have anything to do with condensation but often mistaken for it.

The only additive needed is a cetane booster.

 

[Chris Patterson]

If it was good fuel to start the winter with, probably not. I really hesitate to say that though, sight unseen, whatever. At least drain the Racor, fire it for a few minutes, and then drain again. If there is any water in the cup after running it for a minute, yeah, just drain it. Or "polish" it. As the machanic in me I had to say these things.
However....if it were my boat..I'd probably light it up. A good filtering system is gonna let you know fairly soon if you need to rehab the fuel system..

 

[Warren Milberg]

I believe that diesel fuel does degrade over time due to oxidation and contamination. So it is probably worth the effort to take a sample and check it for water. If it is ok, what I recommend you add to your tank, in addition to a cetane booster, is enough clean and fresh diesel to fill the tank and to "improve" the average age of the diesel already in the tank. If significant water is present, the tank will need to be drained, preferably from the bottom.

 

[thinwater]

Another common myth disproven by various studies. Condensation in the tank is possible but only in trivial amount....

No.

http://sail-delmarva.blogspot.com/2013/03/diesel-and-condensation.html

Gallons of water? No, nothing a separator can't deal with. Enough to accelerate corrosion, certainly, and that has been proven in a number of studies. The samples that disprove this are generally ignore or misunderstand 2 key factors:
1. Climate. Florida may be humid, the but the temperature swings are not nearly so great as further north, where the difference in temperature between the air and water can easily be 30-40F in the spring and fall. Huge difference.
2. While a tank does not condense a great deal of water, none of it leaves. This is because the drops fall into the oil, go to the bottom, and are sealed in. There is also absorption. It is not a simple calculation. Statements to the effect that "an empty tank does not fill with water" miss the point entirely and should be dismissed out of hand as uneducated in the field.

Biobor is a good start. That will keep bugs from growing. Also consider a corrosion inhibitor. Also consider a silica gel vent filter.

 

[Benny17441]

I would like to see one of those studies that minimize the volume of condensation that takes place in a partially filled fuel tank. When condensation takes place inside the tank the water runs down the sides into the fuel and goes to the bottom. With changes in temperature the volume of air expands and contracts breathing in and out through the vent hole and reacquiring humidity equilibrium with the outside air. With the heating of the days and the cooling of the nights the cycles repeat dumping new droplets of water into the bottom of the tank. This is un-emulsified water that will rest at the bottom of the tank until drawn out. By filling up the tank with fuel and reducing the volume of air the amount of condensed water is reduced (simple physics). If the studies meant to infer that a certain amount of water present does not significantly degrade the fuel to the point where it affects the engine's operation that is a different thing than indicating that the amount of condensed water is minimal. I agree when the boats are used frequently there are no side effects but believe that when storing a boat for long periods of time in humid environments subject to frequent temperature changes that it would be best to top off the tank. That and the use of bio additives will prevent fuel degradation. SailSail the problem you might encounter is the settling of some dead bacteria at the bottom of the tank. The fact that you used Biofor may have mitigated the bacteria growth. Just run the engine, drain and replace the water separator filter and add some new diesel fuel. Just be prepared when you go offshore or get into some unsettled seas for the possibility of stirred dead bacteria to clog the separator filter. There are parts of the country where condensation is not a problem but we find that here in the Gulf Coast of Florida it magnifies itself. We are always thinking about topping the tank but also looking for excuses to use the fuel before it degrades.

 

[thinwater]

I've done this same experiment with silica gel filters, same basic result.

 

[Charles Erwin]

Assume the tank was partially full but had a valve in the vent-line that remained closed during layup periods.

What is your opinion about whether water vapor (or the natural water content of the fuel itself) represents any threat?

Charles

 

[Don S/V ILLusion]

I would like to see one of those studies that minimize the volume of condensation that takes place in a partially filled fuel tank.

There are a few done over a period by the Navy. Unfortunately, I have the hard copy but not a PDF version. The link below is based upon on such Navy study method. As there is little exchange between the tank and the ambient air, something the Navy also included in their analysis, this one is essentially a duplicate summary:
http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

Old myths like this, batteries on concrete, etc... die hard.

 

[centerline]

Another common myth disproven by various studies. Condensation in the tank is possible but only in trivial amount. If you want to verify the quality of your fuel, remove the gauge sender or return line and suck a small quantify from the bottom by inserting a ubiquitous oil change pump tube to the tank bottom, let it settle and you can easily see if any water is present.

If water is present, it is likely a result of rain water entering via the fill cap or vent, neither of which have anything to do with condensation but often mistaken for it.

The only additive needed is a cetane booster.

I will respectfully disagree with some of this... or at least clarify..

it is an absolute proven fact that a partially filled tank DOES sweat, condensate, and it CAN accumulate a substantial amount of water in the tank over time.
and a full tank cannot do this.
and it isnt just a boat thing, but fuel tanks everywhere, whenever the tank vent is exposed directly to the outdoor atmosphere, there will be some condensate issues within the tank. some more than others..

there are many reports and articles about fuel tank condensation, and ways to prevent it... the easiest and most common is to keep the tank topped up.
it is usually not a problem for systems that get regular servicing of the filters and clean fuel. it still is a happening thing, but its not being noticed because the filters are being changed in time to prevent a notiecable problem...



the variables are, how big the tank is, the humidity factor, how much volume the tank has above the fuel level, the outside air temperature, and the temperature difference between the inside of the tank and the outside air.

a vented tank breathes with every temperature and barometric change in the atmosphere... the moisture can condensate if the conditions are right, which is quite often.

ALSO, diesel fuel is hydroscopic, which means it will absorb/suck moisture from the air that is in contact with it, so the larger surface area it has in contact with the air, the more moisture it can quickly collect. this is in ADDITION to the condensation factor.
AND, in addition to water, oxygen will cause the fuel to degrade rather quickly. so with a larger surface area there is for contact, the quicker it will cause the fuel to degrade.

by filling the tank up, you have a very small volume of air that is exchanged during the "breathing" of the tank,and as a result there is less moisture carried into the tank in that small amount of exchanged air.
and, there is less surface area exposed that can condensate the moisture from that air.

the marine enviroment has a high moisture content in the air, and the warmer it gets outside, the more moisture the air can hold.... when it gets sucked into a partially filled fuel tank that is cool and shaded, the warm air will condensate on the sides of the tank. when it condensates it makes room for more air..... as soon as the tank warms up a bit or the barometer changes, the tank will expel the old air and then be waiting to suck in more moisture laden air as soon as it changes again.... almost every morning and every night (temperature change), and during a barometer rise or fall there is an exchange...

and it may be only a couple drops of moisture every few days, but it adds up.

with all this said, im sure you wont collect gallons of water in a small tank, but its possible to collect enough in a few months to cause you troubles with your filters.... so it really doesnt matter if its a cup or a quart you collect...
there is a way to minimize the condensation process and minimize your worries and troubles....
but also keep in mind, what water comes in with the fuel during a fill up is just as bad and causes the same damage/problems...

a cetane booster can help old fuel, but if the fuel has degraded too far, it will only give you a false sense of hope....
never use a product the claims to remove water from the tank... only a pump can do this. any additive you try to use to pass water thru the system, is only doing harm to the system.

Seafoam can help stabilize the fuel, and clean your pump and injectors, but there are other brands that do this also.

 

[centerline]

There are a few done over a period by the Navy. Unfortunately, I have the hard copy but not a PDF version. The link below is based upon on such Navy study method. As there is little exchange between the tank and the ambient air, something the Navy also included in their analysis, this one is essentially a duplicate summary:
http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

Old myths like this, batteries on concrete, etc... die hard.

this link is someones misinformed opinion...

there are too many very obvious mistakes in it that can clearly be seen by someone with many years of mechanical experience...
point by point i could show where he has assumed wrongly.
he may call himself a marine surveyor, but when you post information and figures that have no significance other than based on a personal opinion, and try to pass them off as a fact of life, you tend to lose credibility with the ones that actually have seen and know what is and what isnt... on that subject.
and as for him being a marine surveyor, I dont know,..... but i do know there is a huge difference between being certified and being qualified... and its too bad the two dont come together more often.

he does have a nice website and some good information, but not all of it is necessarily the final word on the subject.... he also states that at 1800hrs your marine engine is used up and needs a rebuild, which I strongly disagree with. (BTW..1800hrs is the "timeout", or required change out time regardless of how well it runs, for an engine used in Sikorsky helecoptors. but then falling out of the sky is an entirely different situation than is floating on the water)

some of the figures may correct, but what he is assuming without proof, throws the answers askew and doesnt mean anything... i could post the same thing with assumptions of my own to show proof of my opinions... but its a waste of my time.

you can either believe it or not.. and the ones that dont care to know can learn as they go

but this is all just my opinion....based on actual on-the-job experience.

 

[centerline]

Assume the tank was partially full but had a valve in the vent-line that remained closed during layup periods.

What is your opinion about whether water vapor (or the natural water content of the fuel itself) represents any threat?

Charles

Charles, if the tank cant "breathe", the amount of water in the trapped air inside the tank may condensate out, but it will be an insignificant amount, and the tank wont be able to breath anymore moist air in or out... the fuel will be as safe as possible.

and as Warren Milberg said, in respect to most marine fuels, its air (oxygen) and contaminates (water) is what degrades/oxidizes the fuel.
keep it clean and sealed and there is no problems for a long, long time....

for anyone disputing the condensate issue, you only have to look as far as the inside of a steel tank to see some of the effects of the problem.
any old steel tank that has been around for ages, but has been kept full, will be a clean tank on the inner sides and top, but even a 5yr old tank that is kept only partially filled will have rusted walls and top... you can use a bore scope thru the gauge hole to view yours...

this rust doesnt mean too much now, but in time it can mean a lot....

and, almost EVERY tank that has rusted walls and top, has a rusted bottom, Why?.. because water vapor has condensed on the surface and settled out into the bottom of the tank... and water will rust the tank at the bottom even though it has fuel over it....

its good practice to keep the tanks topped up whenever possible and for long term storage, but understandably its not always practical.
so just know the problem is a something that accumulates over a period of months, not over night or weeks..

 

[Ralph Johnstone]

Another common myth disproven by various studies.
If water is present, it is likely a result of rain water entering via the fill cap or vent, neither of which have anything to do with condensation but often mistaken for it.

A third and even more likely source of water is that which comes in WITH the fuel if you're refuelling form a poor source.

Condensation ............... unlikely. I tap into the bottom of my tank (using a vacuum oil extractor) every few years and may come up with a few spots of dead algae and few drops of water. The dead algae is courtesy of the Biobor. Primary and secondary filters are always clean as well.

If your fuel was good last year, it's still good this year after being in cold storage for the winter.

 

[thinwater]

There are a few done over a period by the Navy. Unfortunately, I have the hard copy but not a PDF version. The link below is based upon on such Navy study method. As there is little exchange between the tank and the ambient air, something the Navy also included in their analysis, this one is essentially a duplicate summary:
http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

Old myths like this, batteries on concrete, etc... die hard.

I'm sorry, but those are not calculations. They are calculations followed by hand waving.

I've been in the fuel business as a chemical engineer for 30 years. As a part of my work I perfom API 653 tankinspections. 2 things see all the time are corrosion under tank roofs and on the sections of walls not oil coated. Often as not, the underside of the roof is wet. The is condensation during transitional seasons. I don't know what else would explian the common failure of roof support rafters. I'vebeen in a lot of tanks.

 

[capta]

For over 50 years I had also been of the opinion that a tank could get water in it through condensation. Then, I believe it was RichH, posted how it sure would be wonderful if we all could get free water by leaving a tank to fill itself through condensation. Put that way, it sounds completely unrealistic and I no longer worry about condensation in my tanks.
I now think the water that is thought to come from condensation, probably comes in with the fuel itself and is not manufactured by the tank.

 

[Stu Jackson]

A relatively unique California weather phenomenon is what is called the "daily temperature" swing. It can be 90-95F during the say and 60F at night in much of the SF Bay region.

I agree with Don. It's an urban myth.

If condensation in tanks was an "issue" there'd be NO boats here that would ever work.

 

[Chris Patterson]

1800 hrs on an engine before teardown? Whooooo lerd... That may have obsoleted half the boats alive. Even Calder in ProBoat estimates a 4000 hr. 'lifespan' when amortizing breakdown costs. And 4000 is really not a good number either. Most poor diesels are simply murdered by the owners, I think it's some sorta Munchausen hate syndrome..

(That one statement alone un-qualifies anyone from talking diesel).

 

[Don S/V ILLusion]

I'm sorry, but those are not calculations. They are calculations followed by hand waving.

I've been in the fuel business as a chemical engineer for 30 years. As a part of my work I perfom API 653 tankinspections. 2 things see all the time are corrosion under tank roofs and on the sections of walls not oil coated. Often as not, the underside of the roof is wet. The is condensation during transitional seasons. I don't know what else would explian the common failure of roof support rafters. I'vebeen in a lot of tanks.

Our professional experience is quite similar yet our opinions are not. The presence of water in tanks is not proof of condensation but rather easily explained by other factors including the maintenance of water bottoms in large storage tanks such as your example which is not representative of boat tanks.

Are you familiar with either the API study or the various Navy studies on the subject? If not, I will be happy to scan and send you one/all via email.

As to the water content in tanks, all of those studies conclude that the presence of water is a result of the combination of leaking fill caps or water entering vent lines or from "bad" fuel and not from condensation.

 

[centerline]

Our professional experience is quite similar yet our opinions are not. The presence of water in tanks is not proof of condensation but rather easily explained by other factors including the maintenance of water bottoms in large storage tanks such as your example which is not representative of boat tanks.

Are you familiar with either the API study or the various Navy studies on the subject? If not, I will be happy to scan and send you one/all via email.

As to the water content in tanks, all of those studies conclude that the presence of water is a result of the combination of leaking fill caps or water entering vent lines or from "bad" fuel and not from condensation.

Either way, even though peoples opinions respectfully differ on the subject, it really doesnt make as much difference how the water gets in, but the fact that it does get in there is why the filters need changed at all.
AND, I will agree, there is a much higher chance that the bulk of the water that may be in the tank has probably came down thru the filler neck, either by rainwater, seawater or being pumped in with the fuel... condensate is a very small amount except in rare cases.
And, because a small amount of water in the tank can be serious trouble to the running of our engines in a time of serious need, its always best to keep the filters serviced...

on a side note,
the previous owner of the Cal I bought always kept his tanks topped up, because he has always believed as I do.... the filters on the boat have not been changed since '07.... and it still runs great, even at WOT for an extended period. we did 2.5hrs of pre-purchase sea trials, and I moved it from his marina to mine after purchase, but I will be changing them before I leave the dock on our maiden voyage with it.
of course, this doesnt prove anything, except that the previous owner was a bit lax on maintenance...

 

[Gunni]

We discovered about a month after haulout that the marina did not fill the fuel tank when they took it over for haulout. We had requested they fill it.....we have always filled it other years. But they said diesel fuel tanks did not need to be filled. I never heard this before, but as it was after the fact, the tank sat 1/3 filled all winter. We did add Biofor.
Do we need to add something before starting the engine? I have read somethings about moisture condensation and am concerned.

I also keep my tank full during lay-up. Top up the tank in the spring and after a couple of days sitting quietly in the slip pull the fuel sender and suck off a couple of gallons of fuel from the bottom using an oil extractor. What you find will inform your next steps. Gunk and water - buy extra filters and plan to burn down and empty your tank during the season.