Sludge in Diesel tank

[STOL71]

I drained some fuel from the bottom of my fuel tank today and there were about 2 oz (50 ml) of black sludge, then diesel run out freely. The diesel is a bit cloudy. The primary fuel filter is still clean, no problems running the engine, I regularly add a pesticide and fuel conditioner and keep the tank topped up. Should the amount of sludge or the cloudy diesel be cause for concern?

 

[Pete7]

Yes, because you just know it isn't going to get better on its own. You could drain off a small amount on a regular basis but you must check the seal on the fuel tank filler as it sounds like water is getting in somewhere.

Pete

 

[Topcat47]

Yes, because you just know it isn't going to get better on its own. You could drain off a small amount on a regular basis but you must check the seal on the fuel tank filler as it sounds like water is getting in somewhere.

Pete

+1. The black sludge is almost certainly bio-carp. Cloudy diesel is never good. After my latest infestation, I had the tank out and steam cleaned (a much easier job than I imagined) but forgot to have the tank pressure tested. There were a number of pinholes in the welds (it's SS) which the cleaning opened up and I had to repeat the excercise and have the seams ground out around the leaks and re-welded.

You may have got some contaminated fuel during a fill-up, I try to use the harbour commission barge in the Medina for this reason, it has a large throughput of diesel and it's always relatively fresh, unlike some marina based stations.

 

[Trundlebug]

I drained some fuel from the bottom of my fuel tank today and there were about 2 oz (50 ml) of black sludge, then diesel run out freely. The diesel is a bit cloudy. The primary fuel filter is still clean, no problems running the engine, I regularly add a pesticide and fuel conditioner and keep the tank topped up. Should the amount of sludge or the cloudy diesel be cause for concern?

Yes it's a cause for concern because the sludge may be on the bottom in calm waters, but will get stirred up when you go out in a chop. That's when your filters will get blocked, and when you least want it to happen.
My suggestion is to polish the fuel with a water absorbing filter medium (good quality filters to the right spec from the big brands are quite sufficient) and you'll be fine. Cleaning the tank is a bonus if you can do it, but can be a big job.

 

[LittleSister]

On a related note, I'm considering attempting to clean out my tank (GRP, built into the hull sides). I expect to find 35 years' worth of crud and grime in the bottom and tank walls. The access is very small, and it would take forever to propely dry out if water was used for cleaning.

I am wondering is there some other solvent (petrol?) I could sue to wipe down the tanks sides within reach, the residue of which would (a) evaporate more quickly/completely than water, and (b) the residue would not be harmful to the engine in very small quantities in the diesel fuel?

 

[Kwik Decision]

I am wondering is there some other solvent (petrol?) I could sue to wipe down the tanks sides within reach, the residue of which would (a) evaporate more quickly/completely than water, and (b) the residue would not be harmful to the engine in very small quantities in the diesel fuel?

How about just using some diesel? That's what I would try first. I suspect if there's sludge etc you'll need to mechanically clean it, rather than dissolve it in a solvent, and there's a good chance a rub with a diesel soaked rag will do the trick.

 

[steve yates]

I flushed my longbows tank through with petrol, probably put about 5 litres into it. It was fine.

 

[Topcat47]

Diesel, sludge and petrol do not mix well. Cleaning the surfaces with a petrol soaked rag would be more effective as the rag will collect sludge and diesel. A final clean with a rag soaked in neat biocide should kill of any bugs left.

It's not as effective as steam cleaning though.

 

[lw395]

I drained some fuel from the bottom of my fuel tank today and there were about 2 oz (50 ml) of black sludge, then diesel run out freely. The diesel is a bit cloudy. The primary fuel filter is still clean, no problems running the engine, I regularly add a pesticide and fuel conditioner and keep the tank topped up. Should the amount of sludge or the cloudy diesel be cause for concern?

Sounds like you have a sump at the bottom of the tank you are draining from?
That is not a huge amount of sludge.
The cloudy diesel is probably a result of the magick additives emulsifying some water into the fuel and/or breaking down dead bug.
You might well be better off without this, just drain off any water from your sump every month or so?
And if you keep finding more than a small amount, find out where it's getting in.

 

[raven]

Agree with Trundlebug that the sludge is pretty harmless in calm waters whilst the diesel is drawn-off from above it, but in rough weather the boat and the diesel gets thrown about and then the engine stops - I speak from bitter experience because this is exactly what happened to me.

Much better to deal with the issue whilst comfortably on your mooring than whilst the boat is getting tossed about in the bay.

In my case the cause of the problem was traced back to a missing rubber o-ring on the deck filler seal. It had allowed sufficient water into the tank to allow the black gel to form at the bottom of the tank. I used the opportunity to cut an inspection hole in the top of the tank so that I can check it regularly and, if I ever need to clean the tank again, I can do so easily.

I also use a diesel additive to try and deal with any water / condensation that does find its way into the tank.

 

[Sandy]

When did you last clean the tank?
Mine comes out every three years for a steam clean.

 

[Trundlebug]

When did you last clean the tank?
Mine comes out every three years for a steam clean.

Wow. That's very fastidious of you, but seems considerably over the top IMO.
When's the last time you steam cleaned the fuel tank in your car?
Better to change the fuel more regularly (i.e. use more), stagnation is the biggest enemy of clean fuel.
But even so, if your tank has been steam cleaned and then you use fuel treatment (biocide) regularly, you really shouldn't need to clean the tank for at least 10 years. Seems a lot of unnecessary effort to do it every 3.

 

[MM5AHO]

There's an article on one method of cleaning a diesel tank of sludge here.. http://www.knoxanchors.com/diesel-bug-pump
Relies on having a short filler pipe into the top of the tank. The pump can be easily DIY made, or bought made up.

 

[Pete7]

Geoff, sadly my experience of building and then using a home brew filter system wasn't great. The problem is the contamination on the sides of the tanks had the look and consistency of marmite, the sludge on the bottom of the tank thick cut marmalade which I used a 2" wallpaper scraper to remove. Using a filtering system didn't do anything to remove these, only opening up the tank and cleaning by hand was effective.

 

[A1Sailor]

A small shovel on the end of my long arm, cleaning rags, pressure wash and steam clean:

:encouragement:

 

[ffiill]

If you can access the tank one of those absorbent multi strand floor mops works wonders whether diesel water or sludge.

 

[A1Sailor]

Nappies are also useful...

 

[lw395]

Geoff, sadly my experience of building and then using a home brew filter system wasn't great. The problem is the contamination on the sides of the tanks had the look and consistency of marmite, the sludge on the bottom of the tank thick cut marmalade which I used a 2" wallpaper scraper to remove. Using a filtering system didn't do anything to remove these, only opening up the tank and cleaning by hand was effective.

The sludge you can't remove with a pump, agitation and filters probably isn't going to get into the engine filters.
The point of such a rig is really to keep your fuel clean, by regularly removing water etc before problems occur.
Letting it get to the point where it needs steam cleaning after 3 years seems like asking for trouble after 18 months?

The OP is lucky, his tank has a sump. Regularly drawing off any water instead of using potions to mix the water into the diesel might be a better idea?

 

[MM5AHO]

I use my small pump on my own tank annually. I get somewhere between 100 and 500ml of diesel that I have to dispose of, with sludge and muck in it, and then it runs clean.
It surely doesn't clean down the walls of the 43 year old stainless tank, but I have only once had a fuel filter block with that black gunk. In that case the boat movement was so violent as to risk structural failure - got caught in some very heavy weather. That was before I started annual "vacuum cleaning".
Of course it is always better to take off the hatch and fully clean the tank, but that can't be done every year without major hassle.

 

[A1Sailor]

You can suck out from the bottom of a tank using a PILA pump...