Fuel tank empty or full?

Greetings

I have a Mainship 390 with 2 diesel tanks. Each tank is 150 gallons. As winter is approaching, should I fill my fuel tanks or leave them at 1/4.

I've been told that condensation could be an issue if the tanks are not filled.

Algae issues?

I'm located in Mystic CT.

What say you? Recommendations?

Thank you for your time.


Ron

0025 said:

Greetings

I have a Mainship 390 with 2 diesel tanks. Each tank is 150 gallons. As winter is approaching, should I fill my fuel tanks or leave them at 1/4.
I've been told that condensation could be an issue if the tanks are not filled.
Algae issues?
I'm located in Mystic CT.
What say you? Recommendations?
Thank you for your time.

Ron

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Condensation is nasty stuff in metal fuel tanks.

IMO and only MO, fill the tanks add a chemical (many brands on the market) that will "preserve" the fuel and rest easy. Every time I fuel, I add the chemical, in the proper amount, to the tanks prior to fueling.
I doubt if the price of fuel will decrease so you will be a jump ahead for the next season too.

Cannot speak for other but last winter I kept my tank a bit lower than half full and I had no issue when back in the water. My tanks are FB not metal and winter is pretty dry up here (too cold to be wet lol)

L

Does Julia Roberts really work in the pizza shop?

I always used to fill up before winter and add stabilizer. The when we were getting ready to sell the boat I decided against adding another $2K of diesel (900 gal/2 tanks), so tanks remained 1/2 full for one winter. I did add stabilizer. No obvious effect on fuel quality. No water detected in Racors. Nevertheless, I still think best approach is to top off.

I owned a 30' Hunter sailboat for 25 years, diesel. Never once concerned myself with how much fuel was in the tank at storage time. Never had any problems. My Silverton with storage for 300 gallons gets put to bed with whatever is in the tanks. Twelve seasons so far... no problems. Both the Hunter and the Silverton used aluminum for tank material. OH--- no additives either.

I routinely keep my tanks at a low level. Never had any water issues. I don't fill for the sake of filling.

For 25 + years in the Ct area I have always had between 5/8 and 7/8 for winter and no additive.

My charter boat sits on the hard 6 months a year in Maryland. Usually has less than a quarter tank with no additives. Hasn't been a problem in the last 18 winters. Personally, I'd rather have mostly fresh fuel in the spring as opposed to old with additives.

Ted

Don't worry about the water but you might want to fill your tanks. A boat can be an independent source of domicile in a emergency where your house or electric and water supply are gone. I look upon my boat as a possible emergency shelter.

The fuel level is up to you.

Algicide is a good idea if their is any trace of water in your tanks. Water may come from a bad supplier, or from leaky o-rings in your filler fittings. Condensation does not add any measurable amount of moisture to diesel tanks. That is an old wive's tale.

I don’t worry about condensation. There have been lots of heated debates on the issue but I’ve never been convinced it really is a “thing” on boats like ours.

On my sailboat I would fill up with fuel in July, and then never fill again until the next July. Only a 50 gallon tank but never had any water in the fuel. Because I kept my fuel so long I did use a fuel stabilizer but with the fuel I would buy I don’t think it was necessary.

Now on my North Pacific, I don’t worry about it. I have been filling the tanks full when I fuel up but that is primarily because I don’t have fuel in my home port so it saves trips.

I am moving from 200 gals. of fuel to 500 gals with the new boat we are getting, and the idea of carrying around 3,500 lbs. of weight, if not needed, is not something I want to do.


I always tried to keep my tanks full in between use due to the condensation issue. On another website I frequented, the verdict was it can happen. The majority on here; its not an issue. I will go with this forum's input. But if I get water in my tanks, I am going to complain.


Eye, I second your comment regarding the boat being a good place to keep food, water, and fuel in the event of an emergency. They make a great hot spot for us west coasters if/when the big one hits.

Fletcher500 said:

I am moving from 200 gals. of fuel to 500 gals with the new boat we are getting, and the idea of carrying around 3,500 lbs. of weight, if not needed, is not something I want to do.


I always tried to keep my tanks full in between use due to the condensation issue. On another website I frequented, the verdict was it can happen. The majority on here; its not an issue. I will go with this forum's input. But if I get water in my tanks, I am going to complain.


Eye, I second your comment regarding the boat being a good place to keep food, water, and fuel in the event of an emergency. They make a great hot spot for us west coasters if/when the big one hits.

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Boats easily take earth quakes in stride. However... they do hate tsunamis!

Why add weight to a boat that will be sitting on the hard?

Your filters will take out any water and a biocide will kill any bugs.

Gasoline boats should have as empty as possible tanks , so the spring fuel fill will mix the old ethanol/water logged enough so it will burn.

O C Diver said:

My charter boat sits on the hard 6 months a year in Maryland. Usually has less than a quarter tank with no additives. Hasn't been a problem in the last 18 winters. Personally, I'd rather have mostly fresh fuel in the spring as opposed to old with additives.

Ted

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Me too.

If condensation was going to be a problem, it would occur in aircraft where the tanks (wings) are out in the air exposed to rapid temperature changes as the sun goes up and down. I had this fight endlessly when I managed aircraft as believers in the condensation bogyman wanted the tanks kept filled. That left pilots who wanted the exchange fuel weight for passengers or cargo on shorter trips stranded.

I prevailed. Aircraft tanks are checked for water by draining from the bottom before every flight. Our aircraft had carefully maintained and tight fuel caps. In all my flying years, I never saw a drop of water.

A professional filtration specialist also pointed out to me that diesel fuel does absorb water which does the injectors no favors. The less fuel in the tanks over the winter, the less water will be absorbed and the more it will be diluted with the spring fill up in the unlikely event that any does get in.

If you find a puddle of water in the bottom of your tank or filter bowl, it almost certainly came with the fuel (very common) or from a bad seal in the deck fill. It didn't come from condensation.

FF said:

Why add weight to a boat that will be sitting on the hard?

Your filters will take out any water and a biocide will kill any bugs.

Gasoline boats should have as empty as possible tanks , so the spring fuel fill will mix the old ethanol/water logged enough so it will burn.

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I agree with you in general terms. In that, new gasoline from good/clean source for boating season start can't help but to be better that old fuel from a year ago.

However... here're some "gasoline" items I've experienced:

1. Gasoline powered 350 cid Chevy engine ski boat I purchased several years ago from my son. It had not been used for six [6] years; maybe a bit longer [I know, he lives two doors down]. I had to take out its encased, half full, plastic gas tank to do repairs on transom. Amazed me to see and smell that the gasoline seemed fine. So... I figured let's do a test. I poured that gas into 5 gallon plastic portable gas cans... as I recall it filled two and partial in a third. Then - I used that six year old gas in my weed eater, and I used it in my 20 hp. commercial concrete mixer, and I used it in my 200 lb ground compactor, and I let one truck [high performance 350 cid Chevy engine] go near empty on one of its tanks and poured 5 gallons of the 6 yr. old gas into it. Result... I had no problem with any gas engine using gasoline that had set for six [6] years. And, the interior of the gas tank out of the boat was darn clean inside.

2. We pulled out a commercial mortar/plaster mixer a few weeks ago that had been sitting for nearly two [2] years. It's 12 hp. gas engine's tank was 1/2 full. I sprayed a shot of starter fluid in its carb and it started on first pull. I let it set running in place for about 30 minutes to make sure all was well before towing it to a project... it never missed a beat!

Additionally: I've found over "decades" of experience that it is best to NOT run gasoline engines dry and to NOT turn off the fuel line. My problems with lacquered-up carburetor interiors and fuel lines each occurred when there was no fuel left in the line. That said, while still leaving gas in the lines... I do recommend unhooking the fuel line where it clips onto any outboard motor. Reason: Heat expansion in gas tank will push enough pressure onto the fuel line that goes to the outboard so that at the hook up on motor location it will seep onto the motor's exterior parts; leaving an oily ugly mess if left attached during too long a time in summer heat.

So... In closing: I'm not clear about all the hub-bub regarding fuel separation in gasoline. Although I've other stories to tell about utilizing old gasoline with no problem... I feel these two stories suffice to get my experiences/point across.

Happy Boating Daze! - Art

I have never seen any proof that full tanks or empty tanks matter either way. People on all sorts of opinions based on other people’s opinions, but only MaineSail has even done what I see as a “test” on the matter. He discovered that there is no significant water build-up in an empty tank. Not scientific by any means. It really only says that... it doesn’t matter either way. Tanks full or tanks empty adds no more water to the fuel that would, in any way, degrade the operation of motors our size.

My experience....no harm in running 4 cycle gas engines dry.

My experience....leaving gas in a carburetor leads to carburetor cleaning at a professional level.

I have towed MANY boats where phase separation in ethanol fuel has occurred.

Roger Long said:

If condensation was going to be a problem, it would occur in aircraft where the tanks (wings) are out in the air exposed to rapid temperature changes as the sun goes up and down. I had this fight endlessly when I managed aircraft as believers in the condensation bogyman wanted the tanks kept filled. That left pilots who wanted the exchange fuel weight for passengers or cargo on shorter trips stranded.

I prevailed. Aircraft tanks are checked for water by draining from the bottom before every flight. Our aircraft had carefully maintained and tight fuel caps. In all my flying years, I never saw a drop of water.

A professional filtration specialist also pointed out to me that diesel fuel does absorb water which does the injectors no favors. The less fuel in the tanks over the winter, the less water will be absorbed and the more it will be diluted with the spring fill up in the unlikely event that any does get in.

If you find a puddle of water in the bottom of your tank or filter bowl, it almost certainly came with the fuel (very common) or from a bad seal in the deck fill. It didn't come from condensation.

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Roger,

Agree. And re aircraft, I've operated them for 40 years, and the only water found in tanks was because of a failed fuel cap o ring. But I replaced those on schedule and never got a drop of water out of the tanks (170 gal), and often filled before flight, so could sit several days with 1/4 tank. And many of the flights had a 100d temperature change during the flight.

Same in my boats. I operated one that was rarely topped off, perhaps once every 3 or 4 months and operated a few times a week. No issues.

Totally an old wives tale.

psneeld said:

My experience....no harm in running 4 cycle gas engines dry.

My experience....leaving gas in a carburetor leads to carburetor cleaning at a professional level.

I have towed MANY boats where phase separation in ethanol fuel has occurred.

Click to expand...

IMO:

Soltron - For fuel separation and water removal and bacteria removal: https://www.navstore.com/soltron-en.html

Berryman B-12 Chemtool - For severe fuel line cleaning: https://www.berrymanproducts.com/pr...-carburetor-fuel-system-and-injector-cleaner/

Seafoam - For mild fuel line cleaning: https://seafoamsales.com/

That's my story and I'm sticken to it! - LOL

Nothing prevents phase separation except the lack of water......

psneeld said:

Nothing prevents phase separation except the lack of water......

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http://www.franklinfueling.com/media/397357/ffs-0238-phase-separation-whitepaper-07-12-web.pdf

Tom.B said:

I have never seen any proof that full tanks or empty tanks matter either way. ... it doesn’t matter either way.

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Tom points to Compass marine's "Mainsail" who has done experiments with the "water in fuel" question." (I read a lot of Mainsail's posts which I consider to be excellent!) Here's another expert on the subject.

The Myth of Condensation in Fuel Tanks by David Pascoe: Boat Maintenance, Repairs and Troubleshooting

What do I do after obsessing over this questions for years? Nothing!
On my last 4 boats it didn't matter if the tanks were full, half empty or empty.

Art said:

http://www.franklinfueling.com/media/397357/ffs-0238-phase-separation-whitepaper-07-12-web.pdf

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Isn't phase separation with ethanol gas?

Is it an issue for non ethanol gas, or diesel?

Ive never had an issue, but occasionally use sea foam. Helps, but also helps with clean injectors, too. (don't know why they need cleaning, but someone sold me on the product).

Pterry sure the Franklin Fuel article tells you when you have it or about to by means of a detection system, not a pour in prevention. To protect customers equipment.

As far as I know nothing can prevent it as of today except keep free water out of it. The EPA is convinced watwr vapor alone probably wont cause it.

Yes any level of ethanol and it can separate out, the higher the concentration the worse it is.

Lots of short articles on the web describing it, how to avoid it, how it damages equipment, etc.

Folks seem to worry a lot about winter fuel storage. Its easy to get mislead by RH, ppm, vs temperature. It's ppm that describes amount of water. It's RH that describes how close to condensation you are, and its all widely affected by temperature.
Some samples:
At freezing temperature (0 deg C), 90% RH air contains less water than 21 deg C at 30% RH. So, this cold air entering the tank as it "breathes in" is quite dry, even at 90%. Yes, if the tank wall cools much below 0, while that 90% air is sitting on top of the fuel, it will wet down the surface of the internal non-wetted part of the tank. Ultimately, some of this will run down into the fuel, and either be absorbed by the fuel or, if its at saturation, fall to the bottom. Its always the free water at the bottom that is the issue for a motor.

Looking at free water at the bottom of a tank, if things are at equilibrium, means the solution in the tank is 100% RH and what water remains, sits on the bottom. In other words, fuel will always contain water but usually at the 100 to 200 ppm level, if there is no free water at the bottom. This would be harmless, unless you happen to go to the artic, and lots of this water settles out.
How much water it will hold is a function of temperature. COLD, excess water may sit on the bottom. Warm up the fuel, and the free water may go back into suspension.

What I have seen in boats is never enough condensation to cause measurable free water in one years time. I'm sure it's possible, but i've never seen it. I've seen lots of salt water in tanks and lots of rain water in tanks.

One other point (sorry). Let's say you have a 1/4 full tank going into winter. If, at the end of a long, wet winter, with lots of hot/cold air cycles, you could have some free water sitting at the bottom due to condensation. The fuel is fully saturated. Now comes spring and two things happen to the fuel. It warms up and is now able to hold somewhat more water in suspension and the free water goes back into solution. AND, skipper adds typically dry(er) fuel. That can also absorb free water and get it back into suspension. This suspended water runs through the engine without issue. Filters don't much "filter" it, either. Another topic.

Biodiesel: Another animal altogether. Many/most? sources of biodiesel will result in blends that can hold a tremendous amount of saturated water, compared to what I mentioned above for petro-diesel (100 to 200 ppm) at full saturation. Like 1500ppm. If you run biodiesel and have stored this in the tropics with very high ppm, and then the temperature drops much (winter happens) you may find yourself with a lot of water at the bottom. Bio can have 15x the problem of petro diesel.