Plastic fuel tanks -cleaning

[blue-max]

I have 2 large plastic (polypropylene?) fuel tanks located under the berth in the aft cabin. Recently I had an issue with old fuel but there now is a waxy residue on the inside surface of the tank - there is no inspection/cleaning panel - the biggest cut out is for the gauge sender. The tank material is too flexible for a rigid panel to be fixed - I don't want smells or leaks so what should I do to clean the tank and is it possible with this material to have inspection panels. At half length there is a baffle so its impossible to  know the condition of the tank beyond it. Replacing the tanks is not something I want to think  about just yet. 

[tiger79]

If you dose the fuel with biocide every time you fill up, you shouldn't have a problem.  Most fuel tanks are fairly horrible inside after a few years.

[blue-max]

Isn't it a bit late for that now the stuff is there. I know from my previous boat where I had this problem - it took a great deal of effort with boiling water and detergent to get the tank clean and it was made from stainless steel

[tiger79]

I had diesel bug in my old Hallberg-Rassy, in the keel tank which was largely inaccessible.  After fuel polishing, and subsequent treatment with biocide, the problem went away, although the insides of the tank were still coated with black gunge.

[blue-max]

I'd feel happier if I could inspect the tanks regularly and clean if necessary. My neighbour on the hard spent days fitting and refitting an inspection panel to his similarly constructed tank - I wonder if anyone else has tried this.

[Odysseus]

It's been a problem in France for a few years now, adding bio fuel, which leads to the BUG, in "modification" I put my solution to making sure I am ok.

By utilising the viewing pipe holes in the tank. I put a pipe down to the bottom of the tank in the lowest corner and fitted a bulb pump.

This setup allows me to sample the very bottom of the tank in about 30 seconds, peace of mind.

The grommets are proprietary items if you need to replace them. I have some spare if you cannot get them.

Hope this helps.
Odysseus
Bav38

[blue-max]

many thanks for that - I will copy . Tank is fitted with some unused connections so hopefully easy to extract the fuel. Now wondering what to do with the old fuel which does not look so bad. Could I get away with treating and mixing with fresh by slowly transferring from one tank to the other or could this be risky? As the deposit is a brown sticky goo could this mean the bactaria is still alive? Don't black deposits indicate dead bactaria? Still a problem for blocking pipes but perhaps easier to clean. 

[Moodymike]

Do the existing grommets contain a tube to the bottom of the tank?

[Odysseus]

No, you have to put your own in.

Odysseus
Bav 38

[Moodymike]

Sorry to be so dumb, but what size are the tubes and how are the terminated ? They look like plastic fittings.

[njsail]

When we purchased our Bav 40 Ocean cc it had about 40 gallons of untreated diesel in the tank sitting for many years on sticks.    I thought about going the polishing route but ended up deciding to have it hauled away and start fresh.   It was a new to me boat and my baby. In retrospect i think i was over protective.  If i did it again i would probably polish amd treat.    Since im in the US i was hit with a hazaddous waste disposal bill.  Ouch. Welcome to New Jersey.   

There is no easy way to clean a stock plastic tank that i.can see.   I have heard of a number of people who dont have any problem in relatively calm waters with diesel gunk....but when they get into sloppy weather and get bounced around, the gunk in the fuel clogs the fuel filter and you are in the hurt locker trying to change a filter while getting tossed around and covered in diesel.  A little embelishment but not much. always keep a spare filter or two handy.

Just my two cents.

[blue-max]

I have seen an article on another site  where a water tank made from the same material  had a round inspection hatch fitted. I'm wondering if this would suit a fuel tank.

[Craig]

Gunk in the fuel tanks is not a problem unless it breaks loose and gets caught in the off-on switch or your filters. Put a in-line strainer ( not a filter) in the line to catch the big lumpy bits without blocking the line.

Biocides generally kill the bug but may not remove any gunk. Use an enzyme to break up the gunk slowly over a period of time. I have seen Startron remove a big lump of gunk from an in-line strainer after 9 hours of motoring without blocking filters. In fact the filters also appeared cleaner.

If you want to get to the bottom of the tank, remove the fuel pickup or the fuel gauge and insert the tube from a oil pump and suck out the bottom of the tank. Won't remove the gunk on the walls but will remove any water or solid stuff from the bottom of the tank.

Fuel polishing is unlikely to do much as the gunk may not be in the fuel. Also, I'm not convinced a fuel polishing system is of any use as your fuel pump, pumps up to 40 times more fuel than the engine uses, then returns the unused fuel to the tank, effectively polishing the fuel through your filters. Fuel polishing systems only appear to be useful in multitank systems on larger boats when pumping between tanks.

As mentioned in previous posts, many boats in Malta do not use any additives, never clean their tanks but remove their in-line strainers when they get filled with gunk. ( Once every year or two) Their tanks are full of gunk.

Craig
"Shirley Valentine"
Gold Coast
Australia

[blue-max]

In that case my plan will be to extract fuel from the top filled tank  using a simple pump put it into a redundant water bottle - about 18 ltrs add some biocide, keep it out of the sun and see what happens. If it clears or is relatively clear I will add it to the new fuel ensuring the mix remains 2/3 new to 1/3 old. The old stuff was bought in Greece - hence bio fuel added. New stuff is Turkish - al mineral as I understand it.
From experience with a previous boat it was only the stuff at the bottom of the tank was suspect - about 20ltrs, the rest was ok.