Black grime inside fuel tank

[MILLPOND]

I have a 1994 Nauticat 33 and recently the sender unit to the fuel gauge failed. I removed the unit and have ordered a new one. The old unit was covered in a film of thick black sticky grime. The inside of the fuel tank is similarly coated as far as I can see.

I have not had any problems at all with blocked fuel filters, but assume that the grime is diesel bug residue, or is this simply 20 years worth of grime which could be considered normal?

The questions that I want help with are:
1. Do I need to do anything about it? (I would have thought not, after all, I've not had any symptoms of interrupted fuel flow)
2. If so, what is the best way to clean the tank. I have heard that some of the common diesel bug treatments can paradoxically cause more problems by loosening grime and causing floating bits which clog the filters.

Any advice gratefully received.

Thanks!

 

[tolhurstorganic]

Sounds like diesel bug, it is black and slimy and will coat the bottom of the tank but if bad also the sides, I have had experience with this! I cleaned the tanks out with rags and towels having pumped contents into cans a messy job. My tanks have large access panels which helps a lot. Made sure the tanks were as clean as possible before reassembly. Changed both filters filled with fresh diesel and added an inline course filter with see through plastic case, this allow inspection of the diesel as it leaves the tank. For a few weeks there was still some evidence of crud so I changed filters again. I inspect and change filters annually and they seem to be very clean. Still get a few bits of stuff in the inline filter though which I change often, they are a couple of quid each and it only takes a few minutes.
Treated the diesel with Marine 16 and do so each time I fill up. Yes I suspect that the treatment may make the residues disperse into the diesel and possibly add to blockage of filter problems hence the need for regular filter changes.
I have just had a blockage problem in the dip pipe banjo union which looked like diesel bug with a piece of plastic possibly from tank manufacture, took some finding after I replaced all the (clean) filters.
No visible crud in the tank though so I suspect it was an isolated piece of detritus

 

[nimbusgb]

Diesel bug. Empty entire fuel system, flush out tanks, change filters, have fuel polished or do it yourself. Use a good anti bacteral fuel additive and try to avoid condensation.

 

[MILLPOND]

Sounds like quite a monumental task. If I've not had any trouble, do I need to bother? Could I just add a biocide to kill the bug, without bothering to clean out the tanks… Or would this risking things getting worse?

 

[tolhurstorganic]

Yes with some installations it can be a monumental task, but definitely worth it, you really don't want to be caught out with a non starter engine in a dangerous place. I had a near disaster at Beachy Head motoring against a strong head wind when the engine stopped and refused to start, managed to hoist main and sail out of it with not much room to spare!
Checking your filters is quick and easy, change them anyway and you may be ok for a while but see to cleaning the tanks out during the winter when you have no sailing to distract you. 20 years of grime needs to go anyway. If possible fit a cheapo plastic see-through filter to inline so you can have a regular check on any **** coming through then pipes. Good luck

 

[MILLPOND]

Thanks for the advice. There are a few posts about fuel polishing here. Getting the grunge out might be difficult as the tank has baffles. Worthwhile avoiding trouble though.

 

[Pete7]

How bad is it? like my photos in thread number 24 which was after using a home made polishing rig.

http://www.ybw.com/forums/showthread.php?242672-MARINE-16-v-SOLTRON/page3

 

[skipmac]

I just went through this with the 30 year old tanks in my boat. One question. What are your tanks made of? If aluminum then this black grunge is corrosive and can be eating away at your tanks from the inside. I started smelling diesel in my bilge and found some tiny drips on the bottom of my tanks (yes both of them). Pulled the tanks out and found tine pinholes in the bottom of both. Cut about two sq ft from the bottom and found the whole inside corroded and numerous pinholes. All in the lowest point in the tanks where the black goo and water collected.

Bottom line, I highly recommend you clean the tanks. Steam cleaning is the best. And yes it's a pain the neck and other parts of the anatomy as well. Also will end up with gallons of nasty waste to dispose of. But as was pointed out, if you haven't had a problem yet you most probably will at some point. This is not something that gets better on its own, only worse, and I have found the engines always choose the most embarrassing moments to stop.

 

[rivonia]

I know you don't feel like doing but get stuck in and do it. Otherwise you will always have that niggle at the back of your mind. naturally the gunge will block the filters just at a critical moment.

 

[MILLPOND]

Pete7: doesn't look quite that bad, although it's hard to see inside all of the tank due to the baffles.
Skipmac: tanks are mild steel, superficial corrosion to inspection, but can't see underneath the tanks. Looks like a mammoth task to pull both tanks out.
Rivonia: agree - it will only get worse and don't want to have a blockage at the wrong time

Question to all: would an additive such as a biocide or enzyme treatment followed by a professional 'fuel polishing' be helpful?

 

[skipmac]

First, as I understand it, fuel polishing is just pumping the fuel through a good filter and back in the tank. Am I correct in this assumption?

Regardless, at the bare minimum I would do the following.

1. If the boat is on the hard or in a very calm marina so any sediment, water, etc can completely setting into the lowest part of the tank before any other steps I would drain or suck the liquid from the lowest spot into a clear container until I get clean fuel or at least no more water and big chunks of grunge.

2. Polish the fuel.

3. Add biocide or your favorite fuel treatment.

If you want to go one step over the bare minimum

1. Suck out the crude as in step one above and dispose of properly.

2. Suck out all the rest of the fuel through a good filter into jerry jugs.

3. Clean as much of the tank as you can by whatever method you choose: rag on a stick, pressure washer, add a little fuel stir and drain, steam would be best.

4. Inspect the inside as well as you can.

5. Refill tanks. Use the old, filtered fuel if it looks good and you're brave. If you want to go all fresh I have friends that use old diesel in home heaters that burn fuel oil.