New to diesel question

Colvic Watson

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We've been petrol engine users for some time, so diesel is a steep learning curve. We're just about to take possession of a motor sailer with a single 75hp engine and twin large diesel tanks. It has been sitting unused for 16 months with both tanks half full of diesel. Obviously I'm concerned that in that time the dreaded bug has been growing. The cost of the diesel is an issue but rather than have serious problems I would rather junk the diesel if it's 'infected' and start again. One concern is that the surveyor finishes his work in a few days with a sea trial to test the engine and so I have two questions:

1. What can I do to find out if the bug is present?
2. If it is, what steps would you take to remove and prevent?

Thanks for your recommendations.
 

sailorman

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We've been petrol engine users for some time, so diesel is a steep learning curve. We're just about to take possession of a motor sailer with a single 75hp engine and twin large diesel tanks. It has been sitting unused for 16 months with both tanks half full of diesel. Obviously I'm concerned that in that time the dreaded bug has been growing. The cost of the diesel is an issue but rather than have serious problems I would rather junk the diesel if it's 'infected' and start again. One concern is that the surveyor finishes his work in a few days with a sea trial to test the engine and so I have two questions:

1. What can I do to find out if the bug is present?
2. If it is, what steps would you take to remove and prevent?

Thanks for your recommendations.


Simon are you able to take a fuel sample from the tanks. it would be apparent if there were a problem.
when you take her over make sure you drain off any water,fill the tanks & buy a few replacement fuel filters to be safe
 

Colvic Watson

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I can sample the tanks but only from the top unless I run fuel through to the water fuel separator - but is it possible that the bug could be in the bottom half of the diesel but not the top? If so, a sample from the top would be clear. What exactly am I looking for?
 

aluijten

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The diesel-bug actually grows in the separation zone between the water and the diesel in the tank. So assuming there will be only a little water in the tank (if any at all) then the bugs will also reside near the bottom of the tank.
Depending on your vessel there may be a small drain at the bottom of the tank. If so you are lucky. Drain the tanks to see if they hold any water. The bug manifests itself by a brown color in the diesel, instead of a light yellow color.
 

Colvic Watson

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Sorry to be dumb - why light yellow for normal? Maybe I should have said the boat has only had white diesel for many years (moored in Holland) therefore I assume White is normal?
 

aluijten

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Sorry to be dumb - why light yellow for normal? Maybe I should have said the boat has only had white diesel for many years (moored in Holland) therefore I assume White is normal?

"White" diesel is always a bit yellow. The other thing is called Red diesel which is actually dyed with red to make clear the special tax regime it's sold under.

Normal diesel (like for cars) can have different tones of yellow. Depends on the refinery is my guess.

The brown from the diesel bug is quite easy to spot as soon a you drain some liquid from the bottom of the tank.

If you are 'infected' you can add some disinfectant to the fuel, but expect a lot of filter changes as the dead gunk will clog up the filters.
 

sarabande

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it is erroneous to state that the bug grows only in the interface between fuel and water, sorry. There are bacteria which live there certainly, but also diesel bugs which live in pure diesel as well as ones in slightly dieselled water.


You need to establish two things.

1 is the diesel contaminated? So samples from as many places as you can extract them. Directly from the filler, from a drain tap at the bottom, from a fuel line junction, from an accessible tank inspection cover, the water separator, fuel filter, etc.

2 if the boat has been static for that long, then any gunge will have fallen to the bottom of the tank, and a sea test might shake everything up, causing the filter to block.


I'd suggest you remove all the fuel to some 25l cans, and take them ashore to treat them, and then fine filter the fuel and re-use it. Flush the tanks through to the filter with a bit of new fuel, and then if all goes well, do your sea test, with spare filters at the ready. (just make sure you can locate and identify all the filters, as sometimes there is a coarse in-tank filter which must be cleared by reverse blowing.

It is worth doing the job thoroughly, in order to use the tanks with confidence, rather than do repeated fuel changes in the early stages of ownership.
 

alan_d

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So called "white" diesel is not actually white it is a yellowy colour. The term "White" is only used to distinguish it from "red".

A bit like wine then? (Not the taste, obviously.)

If you put both red and white diesel in your tank is it rosé diesel?
 

Seadawg33

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Depending on the age of the boat the tank may need to be scrubbed. I had to do this to my tanks. Cut access plates into each chamber and put something like this in the tank http://www.seabuilt.com/. I am a satisfied customer with no affiliation. Once the hole is cut use a green scrub pad, a scraper and window cleaner with paper towels to clean the tank out. I took the fuel from one tank to the other with a fine filter in between so that the two half tanks filled one tank. I then cleaned the empty tank and reversed the process. It was awkward and messy but it cleared all of my fuel problems. Till my son filled the diesel tank with water.
 

charles_reed

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The diesel-bug actually grows in the separation zone between the water and the diesel in the tank. So assuming there will be only a little water in the tank (if any at all) then the bugs will also reside near the bottom of the tank.
Depending on your vessel there may be a small drain at the bottom of the tank. If so you are lucky. Drain the tanks to see if they hold any water. The bug manifests itself by a brown color in the diesel, instead of a light yellow color.
Unless, of course, it's red diesel.

In my experience the bug can be large masses of floating black "clouds" to little hard pellets of black wax. It seems to prefer high sulphur diesel fuel, though the addition of vegetable oils (common in road diesel in France an Italy) is cited as increasing the likelihood of infection.
IMHO the only safe action is to remove, filter and return all the fuel to the tank - finding the interface at which they grow is very difficult.
 

Seadawg33

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Just to add a bit to my previous post Here is a link to some pictures from my diesel tank. https://picasaweb.google.com/mckenz...key=Gv1sRgCNDps4Gl1ZeflwE#5610378090468755074 It was 22 years old at the time and needed cleaning something fierce. I started with a plastic scraper, then sopped up everything with a bunch of paper towels, from there I used a scotch brite scouring pad and window cleaner, after that I wiped the whole thing down with water and of course cleaned that out of the tank. The inside looked just short of being polished. A couple of years afterwards I still hadn't had a problem when I was in cleaning the tank after my son had filled the diesel tank with water.
 
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