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Old 22-06-2020, 10:01   #46
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Re: Leave a Diesel tank empty or Fill it

I have suggested before, get or make a strainer to fit in the filler. Put a bag of silica gel in the strainer. Fit a stopcock on the breather, turn the stopcock off when leaving the boat for any length of time. Attach some sort of large tag or label to that stopcock, open the cock and hang the tag on your dash before you start the engine so that if it is missing from your dash, you will notice.
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Old 22-06-2020, 19:58   #47
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Re: Leave a Diesel tank empty or Fill it

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Originally Posted by a64pilot View Post
A clean dry tank will most likely never accumulate any water or any other problem, it’s the ones that may have several gallons of fuel left in it and may have significant sludge etc on the bottom that may be a problem.
Maine Sail conducted a test to bust the myth of tank condensation and had an empty tank sit for considerable time and subjected to daily heating and night time cooling and after an extended period it never accumulated even a drop of water.
I believe his test to be correct, but may not be applicable to a fuel tank with fuel in it, the difference in my opinion is the fuel, fuel can absorb water, and can when conditions change drop that water out of suspension, so while I agree an empty tank won’t condense water, it’s possible for one with fuel to do so, possible doesn’t mean will of course, just it could.
However the desiccant filter will prevent any moisture from getting into the tank to start with, or I guess close the vent off, it seems it won’t have enough pressure change to matter.
Closing the vent off would be very simple, just stick a ball valve in line.

The myth of tank condensation continues despite Maine Sail's having thoroughly busted it.


Water in fuel tanks either comes on board in bad fuel, or comes from leaky deck fillers. Deck fillers are the work of the devil. If you have these things, be fanatical about o-ring condition and correct tightness.



Diesel fuel (so long as it has no bio in it!) is a quite stable substance, but it does deteriorate, and it does absorb water from the air. Leaving more fuel in the tank than you need is just more fuel to deteriorate and absorb moisture.


My father was a firm believer in the old tank condensation canard. Every single time when we came back from a cruise, we would fill the tank. Yet -- he suffered from regular bouts of diesel bug and water in the fuel for decades. I have no doubt it was the deck filler.


In this boat, over 11 years, the tank is mostly empty in the winter time. Now, I use the boat year around, but less in the winter. Never a drop of water in the tank, despite the famously rainy, humid, condensatious weather of our usual winter home in Old Blighty. I do inspect the tank regularly to be sure, and I'm careful where I buy fuel, avoiding bio like the plague, and avoiding low turnover outlets.



AND -- I don't have a deck filler. The fuel filler is located a couple feet above deck level, in the side of the house.
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Old 22-06-2020, 20:20   #48
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Re: Leave a Diesel tank empty or Fill it

Side note, can marine diesels burn Jet-A?

I found using avgas (100ll) in my lawn equipment the fuel lasts WAAAAY longer than the crap from the normal gas station.
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Old 22-06-2020, 22:22   #49
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Re: Leave a Diesel tank empty or Fill it

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That depends substantially on where in the world you are, and what material the tank is made of. In humid climates, a near empty tank with breathe. That will result in condensation, may promote diesel-bug growth, and may corrode the tank. .. .

That's what all our fathers taught us, but it's a pure myth. MaineSail busted it with serious testing.


But think about it -- it couldn't work like that anyway. First of all, fuel tanks on boats, depending on where they are located, will not generally change temperature, day or night. Because they are located under the water line near water. I measured the temperature of the inside of my fuel tank a few dozen times, winter and summer, and found that the temperature didn't vary even by 0.1 degree. So if the temperature stays the same, it can't breathe.


But even if the temperature varied, it wouldn't breathe in the way that would cause condensation. For that you need warm moist air meeting tank walls which are below the dew point. But in the day time with everything warming up, the tank will breath out, not in, IF it's changing temperature at all. At night, the air is cool, and if any is breathed in, it should not be possible for it cause any condensation -- the tank would have to be colder than the air, but it's been warming up all day if it's breathing.
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Old 23-06-2020, 02:07   #50
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Re: Leave a Diesel tank empty or Fill it

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Side note, can marine diesels burn Jet-A?

.......
In a word - yes. Lubrication issues might arise regarding the injector pump and some add some oil (2 stroke or ATF) to overcome such concerns. Others mix it with regular diesel.

Is it good idea - probably not but it will run.

Personally I would not try it with a common rail engine except in an emergency.
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