Left diesel filler cap off and it has rained

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Miker

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I went to the boat today to find that I had left the filler cap off for a fortnight, and last night it poured down. I couldn't see any water in the diesel tank but decided not to risk starting the engine, so the best sailing weather for yonks was wasted.

I have a Perkins water filter fitted but don't think that I can rely solely on that. I am going back to the boat on Tuesday, weather permitting. By then I assume that any rain water will have dropped to the bottom of the tank. Do I just drain diesel from the bottom of the tank until there is no sign of water, or bite the bullet and drain the whole tank, and dispose of the fuel, around 20 litres. If the latter, is there any additive which I could use to flush out the tank once it is empty?
 
If you can access the lowest part of the tank by drain or pump then remove a few litres, the water will be visible on the bottom, set aside and take some more out , it should be clear. Put it in to a white bucket, a clean old plastic paint bucket is good for this, you will see what is at the bottom better. You can discard the diesel removed or decant the clean stuff off the top back to the tank to reduce what you have to take to the tip. Give it a remedial dose of Soltron or Startron in case there is still some there. You only need to drain the tank if you are unable to get access to the lowest part of it or if it already fouled. Old contamination will be black globules, fresh water will be clear globules on the bottom.
 
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Miker said:
I went to the boat today to find that I had left the filler cap off for a fortnight, and last night it poured down. I couldn't see any water in the diesel tank but decided not to risk starting the engine, so the best sailing weather for yonks was wasted.

I have a Perkins water filter fitted but don't think that I can rely solely on that. I am going back to the boat on Tuesday, weather permitting. By then I assume that any rain water will have dropped to the bottom of the tank. Do I just drain diesel from the bottom of the tank until there is no sign of water, or bite the bullet and drain the whole tank, and dispose of the fuel, around 20 litres. If the latter, is there any additive which I could use to flush out the tank once it is empty?
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Just drain off the water, replace the filter and move on.
 
Miker said:
I went to the boat today to find that I had left the filler cap off for a fortnight, and last night it poured down. I couldn't see any water in the diesel tank but decided not to risk starting the engine, so the best sailing weather for yonks was wasted.

I have a Perkins water filter fitted but don't think that I can rely solely on that.
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But you probably can rely on the water filter. Logically, just how much rainwater might have got into the tank? Even if it "poured down", you'll probably only have got a few ml of water in, and this should separate out in your water filter over time (it won't just suddenly all migrate to the filter), so by keeping an eye on the water filter you'll be OK. After all, what's a water filter for?
 
The problem is that given the deluges we have had over the last forrtnight and the monsoon conditons last night, the deck could have been awash. As I have a fuel stopcock fitted at the bottom of the tank, I think that I will take the safe option and drain off some fuel/water. What I am undecided is whether to play safe and drain off all the diesel and dump it, so throwing away around £25 of fuel. It might be overkill but I would at least sleep at night.

Thanks for the advice about Soltron and Startron. Can I buy it from local auto shops?
 
As you say, there is a lip but what I can't envisage is how effective it would have been given the amount of rain that fell last night.
 
Miker said:
What I am undecided is whether to play safe and drain off all the diesel and dump it, so throwing away around £25 of fuel. It might be overkill but I would at least sleep at night.
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But why? As others have said, the water and the diesel separate out - visibly. There will be nothing wrong with the clean diesel in the tank.
 
I would tend to empty the tank - if you have a drainage point at the very bottom you could use that - or alternatively pumps used for draining oil also work well (that is how I do it). The water should settle to the bottom of the tank so you could just pour the diesel off or put it through one of those filters that blocks water but lets diesel through
 
I think it is optimistic to presume all the water will ever reach the filter, if you have a clean tank with a drain cock it is worth taking the trouble to decant the bottom of it, other wise it will be busy through the winter breeding the bug. Soltron is available from some motor factors while the Starbrite(American but the same stuff) version is more often found in chandleries, it is expensive but you wont need much, what you do not use you can add to future fill ups. It is an enzyme like the ones in your stomach and is claimed to allow the diesel to digest the water. I came to use it routinely because my last boat had a fuel filler flush with the deck where any water ran over it and the tank was very hard to fill on even a damp day, I was for ever decanting the bottom of the tank with a suction pump until I started using it.. Dr. Mike? Blair at QUB Mech. Eng. Dept. was involved with Soltrons development and testing and if you saw some of their racing motorbikes go you would have confidence in him.
 
I've been thinking again about the best way to drain off the the water from the bottom of the tank. There is not a drain tap as such, only the flexible pipe from the tank bottom to the Perkins water filter. It is this pipe that I thought of disconnecting from the inlet side of the water filter and feeding into a bucket. As I said earlier, there is also a stopcock lever attached to turn off the fuel. If I do so, will I then have to bleed the fuel line after reconnecting?
 
Miker said:
I've been thinking again about the best way to drain off the the water from the bottom of the tank. There is not a drain tap as such, only the flexible pipe from the tank bottom to the Perkins water filter. It is this pipe that I thought of disconnecting from the inlet side of the water filter and feeding into a bucket. As I said earlier, there is also a stopcock lever attached to turn off the fuel. If I do so, will I then have to bleed the fuel line after reconnecting?
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Your fuel pickup pipe is not the right place to drain water -- they are not placed at the very bottom of the tank. If you don't have a drain plug or tap at the bottom of the tank -- as I don't -- then you need to hire a fuel polisher, who will put a hose down through an inspection hatch to the very bottom and suck out all the water.

I would do it if I were you, and don't rely on your filter. If you got a good bit of water in there, your engine might run fine, clean fuel being picked up from a level above the bottom of the tank, until you get into some rough weather and the water gets stirred up and overwhelms your filter. Just at the moment you don't want to be stuck with your head in the engine compartment.
 
probably best to drain the tank, as contaminants (such as aerobic bacteria, gull poo, dust) will have been washed off the deck and into the tank.


This happened on a friend's boat left on a marina for six months, when the O ring had failed. Deck water flowed into the water tank via the low-set filler, festered, and resulted in the flexible tank having to be replaced.
 
If you don't want the problem of disposing of the contaminated diesel I will take it off your hands for free.

OK I am tongue in cheek - just do what the others says and let it settle and all will be well.

Alternatively put it in a diesel car so it gets used up quickly and put fresh diesel in the boat?

I had a problem a couple of years ago where our tank leaked over 100 litres of diesel into the bilge. The boat was hauled out in her cradle so I took a pipe off a seacock and syphoned the diesel out of the bilge into jerry cans and ran the car on it for a few days. I only threw away the very last few litres - the rest was perfect and that diesel had been through my bilge!

Before anyone accuses me of running my car on tax free diesel, it was all tax paid - bought overseas - and I still have the receipts!!!
 
You said it's £25 worth? Ditch it! Use it in your car and get a decent nights sleep!
However if I had to get rid of £250 worth I dont think I'd ever sleep again!!:eek:
 
Thanks everyone for the welcome advice. I've decided to draw off the diesel from the top of the tank using my oil exractor pump. I agree that it is not worth the hassle of decanting the diesel for a saving of £25, and have obtained an old 20 litre oil drum from the local garage to take the diesel to the tip. I have some diesel bug additive on the boat but don't yet know whether it is a suitable water absorber.
 
get the pump or syphon to the bottom of the tank. I used a clear pipe attached to a cane. It will draw out the water first, the clear diesel. That way you only have to remove the bottom centimetre or two. Worked for me with a tank which had had long term water contamination. No problem now for over 4 years.
 
From your last post, I guess this advice is too late now, but....

If you've got an inspection hatch just get one of those cheap siphon pumps and pump a bit out from the very bottom into a clear bowl & let it settle. I do this regularly, maybe every 6 - 12 months just as a precautionary measure.

If you've got water in there it'll settle out quite quickly and you can salvage most of your diesel.

Diesel bug treatment is different from water absorber. The latter is pretty expensive. I have a theory it is just industrial alcohol, but....

I'm sure you won't have to take your diesel to the dump, there'll be somebody volunteering to 'dispose' of it for you pretty soon.
 
If you go to the chandlery they will sell you a cloth bag on a string, inside the bag is a dry powder which absorbs water causing the bag to swell; you drop it in, leave for an hour or two and pull it back out with the string, make sure it gets to the bottom, try rocking the boat a bit, it is a more expensive way to do it, but better than trying to decant all your diesel probably leaving only the water behind. I have forgotten the proprietary name or what hygroscopic crystals the use and can't be bothered to search for it. Myself, I would just use my Pela to pull the water out with the bottom litre or two of fuel.
You seem to be reluctant to believe that the water and fuel are separate with all the water on the bottom in the lowest corner of the tank. You will gain nothing by throwing 20l. of clean diesel out.
 
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