Another new guy question - fuel tanks full or not?

[f508]

I am wondering is it better to keep your diesel fuel tanks full to avoid condensation, or low to avoid algae? This is in California, so it is a mild climate, if that matters. Also, it is an older boat (1982).

Thanks,

Frank

 

[psneeld]

Theres a lot of opinions on this. Some places and some tanks develope condensation, other boats and tanks dont.

So depending, keeping tanks full or partial might depend on who you are.

 

[dhays]

Personally, I don't think that condensation is really an issue. I would keep the tanks at a level that would give reasonable fuel turnover. I have no idea what is reasonable. On my saiboat, I would fill up the tank once a year whether I needed fuel or not. Only a 50 gallon tank. I used a biocide in fuel when I did.

Currently, I am thinking that I would like to put as much fuel in the tank as I expect to use in 3 months. I'm not worried about condensation but fuel freshness.

 

[f508]

I am asking because I have a pre-purchase survey coming up week after next, and I am wondering how they will check the tank integrity. I mentioned filling the tanks up to the owner, and he said it was bad to do that.

Algae, and lugging around a bunch of extra weight were the reasons. He seems like a straight up guy, so I don't think he is trying to put anything over on me. But I feel like I would like some kind of clear assurance on the state of the tanks because the boat is a 1982 model.

It seems like at a minimum topping them up would provide some sort of check. Haven't asked the surveyor yet, maybe he'll have this issue covered.

 

[firstbase]

I don't know enough to really help you on this but filling up the tanks could be an expensive proposition for the owner when you may or may not buy the boat. Second, I don't understand the algae reason as I thought algae grew on the layer between the diesel and any water that exists in the tank? If so that would be at the bottom of the tank. Last, the PO of my boat filled up when he got fuel. Used it down and then filled to the top. Was almost full when I purchased it and I filled it up the day before delivery. It gave me some comfort knowing that they weren't leaking. Seems to me that letting the whole tank get soaked in fuel regularly would help prevent some corrosion, no?

Read all of this with great skepticism...others can help much more than I!!

 

[RT Firefly]

Greetings,
Mr. 508. Algae will NOT grow in fuel tanks. Microbes DO grow in fuel tanks and live in any water (not necessarily due to condensation) in the bottom of the tank and feed off the fuel. When these little buggers die off their dead bodies is the stuff that clogs filters. As has been mentioned, use of a biocide eliminates this possibility.
Extra weight? Of course but if you're that concerned about decreased mileage because of the weight of extra fuel, buy a motor home. Meaning, fuel is one of the smaller costs in boating.
So, filling your tanks is NOT "bad to do" and yes indeed, topping up the tanks would be a test. Maybe this "straight up guy" is hiding something or maybe not.

 

[f508]

I don't know enough to really help you on this but filling up the tanks could be an expensive proposition for the owner ...

I offered to pay for it.

 

[RT Firefly]

Greetings,
Mr. 508. YOU offered to pay for it and the guy still thought it was a bad idea? Take the price of tank replacement off of your offer unless you see those tanks filled.

 

[Giggitoni]

I agree with RTF. I'm kind of a skeptical guy anyway. However, if an owner turns down free fuel, I would assume there is another reason he wouldn't want the tanks full. Have your surveyor spend extra time with the tanks. Check the tops for rust or corrosion, depending on their material. And pay attention to the return line connections, etc. Pressure test???

 

[f508]

Just talked to him again. He believes it is not good to do that because of the algae, but he's fine with me filling it up if I want to.

Is that the best way to check the tanks? This might sound really dumb, but do they pressure test them? Of course I'll find out when I talk to the surveyor, but I'm just wondering.

And thanks again you guys, especially RT, I really appreciate the help!

Thank you!

 

[Peter B]

Just talked to him again. He believes it is not good to do that because of the algae, but he's fine with me filling it up if I want to.

Is that the best way to check the tanks? This might sound really dumb, but do they pressure test them? Of course I'll find out when I talk to the surveyor, but I'm just wondering.

And thanks again you guys, especially RT, I really appreciate the help!

Thank you!

If his only objection was a misplaced fear of algae, (as RTF pointed out), then go for it if you want to really test the tank integrity, fillerup..!

However, for what its worth. my boat is near Brisbane, Queensland, Australia, a climate not too different from Florida I understand - warm and often humid summers, and sometimes quite cool, as like now, in winter. Yet I never have more than half-filled tanks, or less, and I only ever have a teaspoonful of condensate in the primary filter bowl, my filters last so long I just change them about every 5 years anyway, and all I do is add the recommended amount per volume of Diesel Power additive when I add fuel, which is not often, and have never had a moment's trouble with fuel issues. Mind you, my tanks drain from the bottom, so sludge build-up is minimised anyway, but there can't ever be much, the filters last so well.

 

[kapnd]

Just talked to him again. He believes it is not good to do that because of the algae, but he's fine with me filling it up if I want to.

Is that the best way to check the tanks? This might sound really dumb, but do they pressure test them? Of course I'll find out when I talk to the surveyor, but I'm just wondering.

And thanks again you guys, especially RT, I really appreciate the help!

Thank you!

If there is already "algae" present, you are much more likely to encounter problems when the tank levels are low, and the crud can be stirred up by the motion of the boat.

 

[Edelweiss]

I used to be in the "keep them full" camp, but some resent test data I saw indicated, so far as moisture in the tank, it really didn't seem to make much difference. Most moisture was already present in the fuel when it was delivered or leaked in through bad fuel cap seals, etc. Since then I've been keeping them about half full, 200 - 300 gallons, solely for the purpose of turning the fuel over more often.

 

[Ski in NC]

If considering buying the boat, certainly fill the tanks to check for leaks.

I am in the camp that considers keeping tanks full a non-issue regarding condensation. I have two 160gal tanks on my personal ride and mostly keep them around 1/4 full. In nine years and 20,000nm not a drop of water in the Racor ever. But my fill and vents are not exposed to rain, so I think that is the key.

 

[Roamer Blue]

Perhaps the "condensation" mythology was started by all those places in the past that had water in their fuel supply?

I m inclined to call BS, and leave the fuel tanks at whatever level is convenient. Sure makes it better for winter storage and fuel degradation in your favorite old ride.

The extensive regulations that have been put in place over the last 40 years have put a stop to water in fuel at the pumps, where geographically these regs are applicable.

And surprisingly... we aren't having water in fuel trouble like our parents and grandparents had to put up with?

Some myth busting rebel did a test, put empty fuel tank in the garage and open piped it to the outside... no wet at all inside after many months.

Who has the link?

RB

 

[jleonard]

I like to keep mine more towards the full side because I'd rather the boat be heavy/more stabile in sloppy conditions.

 

[Seevee]

Personally, I don't think that condensation is really an issue. I would keep the tanks at a level that would give reasonable fuel turnover. I have no idea what is reasonable. On my saiboat, I would fill up the tank once a year whether I needed fuel or not. Only a 50 gallon tank. I used a biocide in fuel when I did.

Currently, I am thinking that I would like to put as much fuel in the tank as I expect to use in 3 months. I'm not worried about condensation but fuel freshness.

Dhays,

Regarding freshness... is there a real issue? Does diesel degrade over time? I've heard that is does not... to any significant amount. I've got a friend that has been using the same diesel over the past 10 years when I last topped off and no issue. He just doesn't travel far.

As for a biocide, suspect that might keep the filter cleaner?

I'm not in any camp on topping off or not... I just don't ever want to run out at the wrong time, so will fill accordingly, and see little reason to make a partial fill.

 

[Lepke]

Whether the tanks are full or empty there will always be organisms if you don't use a biocide. I do, every time I fuel. Empty allows more condensation. Air in tanks expands as the day warms and contracts as the day cools, drawing in moist night air.
If you use a good biocide, it also has fuel stabilizers and additives that help a good primary filter extract water.

 

[f508]

Perhaps the "condensation" mythology...

RB

Hi,

The condensation issue is fairly well known and demonstrated in aviation, but I am new to the boating thing, so I have no idea in this realm.

Maybe the boat tanks have a more stable temperature because the hull is usually in the water, and water doesn't change temperature as rapidly as air, so condensation is not much of an issue.

Anyway, seems like one less thing to worry about, so that is good.

Thanks

 

[sunchaser]

Some random notions--

Condensation is a major consideration in the design and operation of fuel farms. Now, how similar are our boat tanks to a fuel farm? For most, not very. But once a vessel gets into bunkering large volumes the reasons for condensation mitigation creep up.

Along with what micron rating, adding biocides or not, stale fuel or biodiesel - condensation concerns may or may not be an issue in your case. But, we do wear our safety belts, don't smoke, keep our weight down and wear motorcycle helmets (some anyway) don't we?

Me? Fuller tanks during winter. No downside unless your vessel is not used much and the diesel fuel becomes + one year or so.

 

[dhays]

Dhays,

Regarding freshness... is there a real issue? Does diesel degrade over time? I've heard that is does not... to any significant amount. I've got a friend that has been using the same diesel over the past 10 years when I last topped off and no issue. He just doesn't travel far.

As for a biocide, suspect that might keep the filter cleaner?

I'm not in any camp on topping off or not... I just don't ever want to run out at the wrong time, so will fill accordingly, and see little reason to make a partial fill.

To be honest, I have no idea. I have heard (which means absolutely nothing) that diesel does tend to break down with stuff precipitating out after a few months of being refined. Whether true or not, I don't know.

I think your approach is reasonable. I just don't think that condensation is really an issue on our boats.

 

[bayview]

Over 15 years in hot muggy FL I rarely filled the tanks. Mostly low levels to allow more sloshing to keep junk in suspension. Never had any water.

Never used biocide or any additives either, just dont believe in them.

Tanks mostly leak from bottom corrosion so full or not it probably won't make any difference.

Re the airline comment. Planes cycle frequently through a wide operating temperature. Boats not so much.

IMO most if not all water comes with the fuel or from bad fill O rings.

 

[Seevee]

Hi,

The condensation issue is fairly well known and demonstrated in aviation, but I am new to the boating thing, so I have no idea in this realm.

Maybe the boat tanks have a more stable temperature because the hull is usually in the water, and water doesn't change temperature as rapidly as air, so condensation is not much of an issue.

Anyway, seems like one less thing to worry about, so that is good.

Thanks

F508,

I'm plenty familiar with condensation in aviation and fairly easy to drain tanks from the bottom. What I don't understand, is why boats don't have a sump drain on the bottom of fuel tanks. Would be dirt simple to get the water out. (I guess there's a few that do, but rare). Had I had them on my Formula I could have saved a few $Boat units to fix the problem (bad gas from a marina).

Now, with the plane, I have an air conditioned hangar, which isn't an option for the boat, so we have to deal with condensation.... in the fuel, in the cabin... everywhere.

We can run a dehumidifier which helps a lot (have one for the small boat but need one for the trawler). But the fuel tanks, we're stuck..

Question:
How much does fuel polishing help? Understand that recirculates the whole tank which should keep fuel clean?

 

[f508]

The mention of a dehumidifier brings another couple questions to mind.

Do you just run a drain to the bilge and let the pump push it overboard?

Is there any concern about excess dehumidification? Can it cause shrinkage in the interior wood trim?

The boat I have am in contract on with feels pretty dry inside. So I'd hate to mess things up with too much of a good thing.

 

[dhays]

The mention of a dehumidifier brings another couple questions to mind.

Do you just run a drain to the bilge and let the pump push it overboard?

Is there any concern about excess dehumidification? Can it cause shrinkage in the interior wood trim?

The boat I have am in contract on with feels pretty dry inside. So I'd hate to mess things up with too much of a good thing.

You can have the condensate drain into the bilge, but most folks will drain it into a sink. The idea is to get the water out of the boat. A bilge pump will never get all the water out of the bilge.

You would be hard pressed to get a boat too dry. The only exception may be a wood boat, but even then I would doubt it. I leave the dehumidifiers running 24/7 on my boats.

 

[Seevee]

Hi,

The condensation issue is fairly well known and demonstrated in aviation, but I am new to the boating thing, so I have no idea in this realm.

Maybe the boat tanks have a more stable temperature because the hull is usually in the water, and water doesn't change temperature as rapidly as air, so condensation is not much of an issue.

Anyway, seems like one less thing to worry about, so that is good.

Thanks

Ah, yes, quite familiar with condensation in aircraft tanks. But any water that collects can be drained off with the sump at the bottom of the tank.

Why don't boats have those sumps? Well, I guess a few do, but would be really nice if more had them.

However, I don't get anal about topping off either the boat or the plane. However, the plane is in an air-conditioned hangar which minimizes the problem, a luxury the boat really can't have.

 

[BandB]

I think the "Algae" comment was either sadly misguided or an attempt to misguide you. I would fill the tanks for two reasons. To check the entire system for fuel integrity and to see how the boat runs with full fuel.

 

[FF]

"What I don't understand, is why boats don't have a sump drain on the bottom of fuel tanks.

The inital boat purchasers do not require it ,

so the boat assembler finds it far cheaper to install a box to hold fuel,

rather than a well built fuel tank with drainable or bailable sump.

Modern diesel with a bug killer will last a long time before ashphalting makes the fuel too hard to filter.

Gasoline with ethanol should be kept to a minimum when storing , so a fresh fill will be able to ignore the water the ethanol captured .

 

[rwidman]

Perhaps the "condensation" mythology was started by all those places in the past that had water in their fuel supply?...........

And perhaps it's not a "mythology". That sounds like a line to discredit the opposition.

My boat's owners manual suggests keeping the fuel tanks full to avoid the possibility of water caused by condensation.

Remembering eighth grade science and more recent experience involving cold beverages on hot humid days, my choice is to follow the manufacturer's advice and keep the tanks as full as practical. There's certainly no harm in doing this and a side benefit is, when I'm ready to go somewhere, I'm ready to go somewhere. I don't have to wait for a fuel dock to open.

Maybe somebody could start a business making "cozies" for fuel tanks.

 

[rwidman]

....................... We can run a dehumidifier which helps a lot (have one for the small boat but need one for the trawler). But the fuel tanks, we're stuck..

You can't dehumidify the air inside the fuel tanks and the air outside is irrelevant.

Unlike modern cars and trucks, boats have fuel systems that are open to the atmosphere. Each tank has a vent to allow air to be pushed out of the tank as you add fuel and to allow air to enter the tank as you use the fuel.

By having these vents, there is air exchange in the tank as the fuel expands and contracts with changing temperature. This air exchange brings in moist air which condenses on the cooler fuel and metal tank walls and leaves water which mixes with the fuel.

This will happen less in some climates than others.

The reason for keeping the tanks full is to minimize the amount of air that can enter the tank in the first place.