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Water in fuel


Noggin

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This is becoming a bit of a drag! - I had a fuel-guard fitted last year so I could keep an eye on it and have been doing a daily check as part of the morning routine.  Last time out, I ran the engine for 1/2 an hour, checked & set off - we conked out. The engine was bled, a new fuel filter fitted (was waterlogged) and a drain attached to the bottom of the tank -no water ran out.   New seal fitted to filler cap & I put vaseline all round the filler cap to stop any ingress.  Went down to boat this morning & started up, ran for 10 mins, checked & 1/2" of water in fuel guard (now drained) - would like to put this problem to bed - any ideas???   Thanks 

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  • Dodgy fuel purchased (unlikely, but it does happen)
  • Leak in your fuel tank - from the canal
  • Water getting in through the tank breather (happened to me some years ago)
  • Somebody purloining your fuel and replacing it with water.

 

I'd get a sample of the -whatever it is - from the bottom of the tank, so that you can see the extent of the problem

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4 minutes ago, Noggin said:

This is becoming a bit of a drag! - I had a fuel-guard fitted last year so I could keep an eye on it and have been doing a daily check as part of the morning routine.  Last time out, I ran the engine for 1/2 an hour, checked & set off - we conked out. The engine was bled, a new fuel filter fitted (was waterlogged) and a drain attached to the bottom of the tank -no water ran out.   New seal fitted to filler cap & I put vaseline all round the filler cap to stop any ingress.  Went down to boat this morning & started up, ran for 10 mins, checked & 1/2" of water in fuel guard (now drained) - would like to put this problem to bed - any ideas???   Thanks 

Water / Rain / Splashes getting in the fuel tank air vent ?

Hole in fuel tank and when underway water gets thrown up by the prop and gets into tank (I had this on one boat where the canopy maker had fitted 'poppas' along the stern and one had come off and water got in the hole - if the tank was filled with diesel up to the height of the 'poppas' then it dribbled out into the cut. Eventually a bit of 'chewing gum' solved both problems.)

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How full is your diesel tank?  It's generally a good idea to keep it brim full in winter to avoid condensation.

 

If you start to grow the dreaded Diesel Bug in a big tank full of diesel it's a very bad idea!

 

I agree the posts above that suggest checking how much water you have in the bottom of your tank.  Either use a tube to dip the tank or a pump to get some diesel out of the bottom of your tank, stick it in a pop bottle and let it settle and separate.

 

A friend had trouble with a steel jerrycan that let water in - his topup spare diesel was constantly getting contaminated with water, and he would then blithely tip it into his main tank.  That took some finding as nothing was wrong with his tank!

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Apart from all the above. Because of the usual bow up, stern down attitude of most boats the water maybe pooling at the back end of the tank, away from your drain tap, therefore the boat might need leveling or ideally lowering the bow and or raising the stern so the water can pool forward towards the tap, and perhaps heeling over to the side the tap is on. This can be done either when the boat is level in dry dock on the plinths or put extra weight on the bow end, like fill the water tank right up and put heavy weights in the front well, like 40 gal drums of water,  or get half a dozen Hattie Jaques to stand in there, or what it takes until the boat levels up, mind water doesn't pour in through the wells scuppers if you have them. On seconds thoughts it might be easier, though dearer to just pump it out via the filler.

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Wot Bizzard said. I bought a dead cheap 12v pump off e bay to pump old oil from a car engine (knackered drain plug). That would enable you to get a really good sample of what is actually in the tank, You could even empty the tank into containers with time and patience. Water in fuel is a sod. What you can't see though is the rust and slime that's in the tank and that is damn nearly impossible to get out without an inspection plate bolted onto the tank. I have one and when I had water in the fuel the mess in the tank was horrible. I now remove the plate every year and have a look in the tank. Good luck.

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2 minutes ago, Bee said:

Wot Bizzard said. I bought a dead cheap 12v pump off e bay to pump old oil from a car engine (knackered drain plug). That would enable you to get a really good sample of what is actually in the tank, You could even empty the tank into containers with time and patience. Water in fuel is a sod. What you can't see though is the rust and slime that's in the tank and that is damn nearly impossible to get out without an inspection plate bolted onto the tank. I have one and when I had water in the fuel the mess in the tank was horrible. I now remove the plate every year and have a look in the tank. Good luck.

I am going to caution against those pumps. A far as I can see they are sliding vane pumps with a tiny clearance on one side of the rotor. When using one to drain water from the fuel tank you ae likely to  pick up rust particles and they can and do jamb the rotor. Results - blown fuse, smoking motors, ruined pump assembly etc.

 

On most narrowboats with stern tanks you can syphon the much into empty milk "bottles" easily enough. You could also cobble something to a wet and dry vacuum cleaner but would need clear pipe/hose so you can see what you are removing.

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Like The Biscuits, I'd start by eliminating what is potentially most likely cause in a boat in good condition - condensation in the tank.  This forms where there's air and cold steel above the level of the fuel, so the less space there is, the less moist air and cold steel there is.  If you've kept your tank full, it's unlikely to be that, so there's the first essential question: have you kept the tank full?

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While i don't disagree with Mr Sea Dogs condensation argument and if it were a one off i would consider it... but as you have taken the trouble to drain and check for water before, it seems to be happening a bit too often. I would suspect a leak from a fuel filler cap or through a vent.

 

I think all you can do is try to eliminate the source. Check O rings on fillers caps. Maybe make some sort of rain cover for the vent and see if the problem appears again. I hope it is a simple fix.

Edited by Paringa
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3 minutes ago, Paringa said:

While i don't disagree with Mr Sea Dogs condensation argument... 

 

I hope it is a simple fix.

It's not that I think that condensation is definitely the issue, it's that its very easy to discount it as a cause if his tank has been kept full.  After all, he's had problems before and he thought he'd fixed it - he's already provided a list of other things he's ruled out or actions he's taken to prevent recurrence, and now he has 1/2 inch of water in his agglomerator (which is a tiny amount).  Condensation stands out as one possibility he has not reported on one way or the other.  Obviously,  there's more to be done, but the more possibilities you can eliminate, the closer you get to finding the problem. I like to knock the easy stuff over first.

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I vac mine with a length of copper tube stuck up the vac hose. Heel the boat over to the side with the filler on and you can get the tube into the lowest corner of the tank. Its easier than having an inspection hatch to seal.

 

If you really are taking in water from the canal, check the top of the rudder stock tube through the fuel tank where it is welded to the deck. Its not unknown for them to be tacked only or rusted through. In reverse the water fills the tube and any hole will let it into the tank.

Of course any pinhole in the tank below water level will admit water into the tank without fuel running out, till you dry dock!

 

We had a new boat in the marina which had a rear tonneau fitted. Numpty fitter drilled around the stern for press studs, into the tank!

Next time the tank was filled they left a rainbow behind them. But they would also let water into the tank.

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6 hours ago, Boater Sam said:

We had a new boat in the marina which had a rear tonneau fitted. Numpty fitter drilled around the stern for press studs, into the tank!

Next time the tank was filled they left a rainbow behind them. But they would also let water into the tank.

Exactly what we had - see post #3

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10 hours ago, Boater Sam said:

Of course any pinhole in the tank below water level will admit water into the tank without fuel running out, till you dry dock! 

 

Surely the fuel level would be constant, fuel would leak out till the pressure from the height of fuel matched the water pressure and as you used fuel water would flow in to keep the pressures the same so the fuel level in the tank would not really change. (yes diesel is 90% the weight of water but the few mm difference you probably won't see)

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I was not being too pedantic but it depends where the hole is. If its the tank base on the uxter plate seam then I would expect water to enter if the fuel level was at or below the water level. If the tank was full he may well lose fuel into the cut.

But hey, lets not thrash the monkey, hopefully he has no perforation of the tank.

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Thanks to everyone - I am hoping that it isn't canal water! - the boat is only 2007 & I'm not leaving any trace of fuel in the water & there is no smell around the stern - I intend to have the fuel polished (I am presuming this will remove all liquid from the tank?) and then fill to the brim with fresh diesel - we'll take it from there & I will continue to check the fuel guard daily -hopefully this may be an end to it!

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31 minutes ago, Tony Brooks said:

Or for even less cost try a syphon - unless your fuel tank is on the baseplate.

Yup. Cheap piece of clear plastic tube. 

 

Who’s to say the fuel polishers would get all the crud out of the corners anyway. 

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1 minute ago, Noggin said:

Thanks again - just bought a syphon pump for £2.88 -if it does'nt work, no real loss!

Consider cable-ties to connect the pickup end to a stick. Then you can point it into all the nooks and crannies. 

 

Or a wire coat hanger. 

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31 minutes ago, Noggin said:

Thanks again - just bought a syphon pump for £2.88 -if it does'nt work, no real loss!

 

If you are going to syphon the fuel out yourself, when you get down to the last 20ltr or so, have someone rock the boat to stir up any crud so it gets syphoned out, then put some fuel back in the tank and rock it again, syphoning this back out.

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When I was in the RAF, POL section, we used to dip the 5000 gal tanks every day. On the end of the dip stick we used to put a blue paste that turned green on contact with water, so we could see the water level in the bottom of the tank. Is that paste available commercially?

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6 minutes ago, artleknock said:

When I was in the RAF, POL section, we used to dip the 5000 gal tanks every day. On the end of the dip stick we used to put a blue paste that turned green on contact with water, so we could see the water level in the bottom of the tank. Is that paste available commercially?

Yep. You can get a tube via Amazon/eBay for about a tenner, iirc.  Water finding paste. 

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