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Old 11-04-2008, 01:42 AM   #1
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I'm in the middle of my repower and have just cleaned out my 200 liter stainless diesel tank. I don't want to change it becasue it's a good size, is in good nick and I don't have to adjust any of the mounting. but it has a problem. There's no drain plug in the very bottom, jut the usyual fuel pickup about an inch above the bottom and I'm afraid it will collect water and I won't be able to keep my fuel clean.

I'm tempted to just take a drill to it, but short of welding a fitting on (which I can't do) is there any kind of fitting I can use to add a drain plug? All I need is a spigot that I can hook some clear fuel line to and let the water/crap collect in there for easy draining.

I'm open to any ideas on how to mod it in place. but if welding is the only option then I guess I'll have to manhandle it out and get it to a welder as I don't think it's a good idea to have a diesel tank with no sump/drain.
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Old 11-04-2008, 12:23 PM   #2
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Don't. You do not need a plug in the bottom of your fuel tank.

What you need is a primary fuel filter and water separator through which the fuel will flow before reaching the engine's fuel filter (secondary filter). The most popular filter used in sailboats is made by Racor.

I'm surprised that there isn't one installed. One on line information source here: Marine Fuel Filters

Stainless steel (or most likely Monel for a fuel tank), is most corrosion resistant when it is highly polished with few or no scratches or pits. Welding will introduce pits and crannies where water (heavier than fuel) will collect and corrode. A drain plug just introduces an element that can corrode or fail in one way or another.

You can, and should, regularly check your fuel to be sure that your fuel tank is clean. Fuel sitting in your tank that has not been treated with biocide can get pretty dirty with algae growing in the tank. During your refit you should inspect and clean out your fuel tank, using something that can clean the tank sides. The amount of effort you need to expend is determined by how dirty you find the fuel at the bottom of the tank (pump the fuel out into a clear container to see how dirty and contaminated with water it is).

Another handy device for diesel engines is a vacuum gauge installed between the fuel filter and the engine to warn you if your filter is clogged and flow of fuel to the engine is restricted. With a clean tank and new fuel filters this should read little to no pressure. In our case, it warned us that the fuel filter housing on one of our engines was clogged and/or defective, restricting fuel to that engine.



Some sailboats have installed two filter housings separated by a valve so that they never have to worry about repriming their engine; they can swap out fuel filters by simply switching over to the second filter. replacing fuel filters should be a regularly scheduled maintenance item, just as changing oil and oil filters should be done on a regular schedule.
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Old 11-04-2008, 09:12 PM   #3
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Thanks for the reply. maybe I should have been a little clearer, when I said "repower" I should have said "power". I bought the boat part way through the repower process so most of the engine, and all of the auxiliaries like external fuel filters had already been removed.

You buys a bargain, you gets a bargain :-)

So it may have had one I don't know. But to answer your question yes I'm adding a twin filter and water seperator in the line. Maybe even a pump. I'm also thinking that it would be a good idea to keep an absolutley full jerry can of fresh clean diesel strapped in there somewhere. If bad things happen to the uel supply I can easy switch over to usign that.

I hadn't heard of biocide, I'm reasonably new to boating, but that addresses my concerns about algie. There was a few litres of water in the dregs of the tank (from a year of condenstaion from sitting empty I guess) and it was a bit murky, but the tank cleaned up really well.

I am kind of concerned about the build up of water in the bottom over time from condensation. Is that a real concern? or would most of the water be sucked through and dealt with by the seperator? Am I going to be adding a "drain tank, tip it over and get the water out" to the annual maintenance schedule? I hope not becasue It's a helluva lot easier to do without the engine in the boat :-)
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Old 11-05-2008, 06:51 AM   #4
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Periodically insert a syphon pipe down down to the bottom of the tank to remove any water. Be sure to dispose of this "water" in the correct manner. Keep the tanks as full as possible to reduce condensation.
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Old 11-05-2008, 12:08 PM   #5
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Water is introduced into your tank from condensation, primarily a problem in temperate climates. Algae is a source of water and "gunk" in tropical climates or in places where they don't add biocide to the fuel or their fuel filter at the pump has been removed. Lastly, diesel degrades over time, and in tropical climates has a shelf life of only about a year. Leave your boat stored someplace in the Caribbean for a year and the diesel will be poor quality, as it will be if it's been sitting in some backwater yacht club's tank over the slow season and into the next. For that reason, a good filter system is paramount. In some places where you know the fuel from the pump will be contaminated, there is a "Baja filter" to filter the fuel as it is being pumped into the tank.

We've had several bouts of contaminated fuel tanks, once when we had to leave the boat in Australia for almost a year. The fuel tank was almost full, but it was quite bad and needed to be cleaned up. What we had to do was to pump out all the fuel in the tank, let it sit in translucent jerry jugs for several days, then siphon the bottom of the jug where water and gunk had settled. What was left was combined with additional diesel from the tank, and the settling and siphoning of water/gunk was repeated. When what we pumped from the jugs came through clear without water or gunk, it was returned to the cleaned fuel tank. All told, with limited jerry jugs, etc., it took about a week to reassure ourselves that our fuel and tanks were clean and uncontaminated.

I repeat, though, that a drain plug at the bottom of the tank will create more problems than it will solve.

I have several entries dealing with diesel fuel in my Cruiser's Dictionary in the Cruiser's WIKI. C-D Cruiser's Dictionary
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Old 11-29-2008, 09:06 PM   #6
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Water is also introduced into the fuel tank through the hull vent. Most diesel tanks have a vent line that is mounted on the outside of the hull of the boat. Put the "rail in the water" on a particular tack and that vent is now underwater and will allow some seawater to work its way into the tank.

For two reasons I moved my tank vent up from the outerside of the hull to the side of the cabin top. #1, to prevent water getting in the vent during heavy seas or healing. #2, to save big fines for diesel spills when fueling - now my vent in "on-deck" and I can position a bucket or some absorbent diapers under the vent so that when the tank being fueled reaches "full" and diesel surging up the vent line is not discharged into the sea (especially if a USCG guy is standing about).
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Old 11-30-2008, 01:50 AM   #7
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As far as leaving the boat in Australia and water and other contaminants are concerned.

I purchased one of those fuel filter funnels from West Marine in the USA by mail order after reading about them here and in other places, and after a year where I replaced my fuel filters more than I'd like. After seeing that it slowed the filling down somewhat the fuel wharf operator poo-poo'ed my use of the thing and told me to shove the fuel line directly into the filler hose so he could get on his way a bit faster. At the end of filling my tanks (was just a top up so I only bought about 70L of fuel) there was quite a bit of water, something that could have been chewing gum in a past life, and one dead mouse in the bottom of the fuel filter.

This was at a place that prides itself as having "the cleanest fuel anywhere". Yeah, right.

Needless to say I wasn't offered a refund for the volume of water or the dead mouse, and the ship's cat wasn't interested in going near the thing on account of it smelling of diesel.
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