How to repair a plastic fuel tank

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anniebray

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We have a 35 dia hole in the top of our diesel tank which we have to seal, any ideas?

This resulted from an indescribable bodge job by the boat builder when fitting a diesel heater. Suffice it to say that I am going to take the feed for the heater from the engine CAV filter ( and I know that many think this is bad practice). However I am left with a 35 dia hole which must be sealed. The tank is of Italian manufacture marketed by Plastimo and in the region of the hole is approx 3mm thick. Any ideas how best to fix this ?
 
Have a word with one of your local car bodyshops or one of the mobile guys that repairs bumpers, ie the lower end of the market. Almost certainly one of them will have plastic welding kit for repairing plastic bumpers and wings. Leister kit is good if they have it.

I think panels are made from polyprop, I 'm sure someone will correct me if I'm wrong, so your tank would need to be made of similar plastic - ideally they would need a small area to experiment on.
 
jbweld on ebay will seal anything?????look for yourself.ideal for boats and cheap too.some will even seal under water.may need a disc to cover initial hole on your tank but get the correct weld and will be fuel resistant which your especially looking for.
 
If the tank top is flat I would consider a metal plate held by a number of self tapping screws and bedded on a diesel resistant sealant or a nitrile rubber joint washer.

JB weld is only a filled epoxy. It is unlikely to hold on the plastic the tank is made of. ( polypropylene or polyethylene I'd guess)

CT1 won't bond to polypropylene , I doubt if it will bond to polyethylene either

I hope by 35 diam you mean 35mm not 35cm
 
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Searush said:
Can you get at the inside? If so, use an s/s nut & bolt with a couple of penny washers & a couple of rubber washers cut out of an old inner tube.

Or put a fitting in it & cap the outlet pipe.
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No cannot easily get inside which is why the job was bodged in the first place. Fuelling nozzle, fuel flow & return nozzles (engine), and contents meter were all fabricated by the tank manufacturer. Given the difficulty of fitting the extra nozzle for the heater, the boat builder should have teed off the engine supply IMHO but lets not start a debate on that issue because its been done before on the forum.

Thanks for all replies, I think the plate idea with self tappers & diesel resistant sealant sounds the best solution for me.
 
Surprised no-one has suggested getting the original bodger to pay for a decent tradesman to replace the tank. Or is he long gone?
 
Hole in the top of the tank

Having got an unwanted hole in the tank I think you should make the hole bigger to become an inspection port. ie big enough to get an arm in to wipe out the bottom of the tank to clean it thoroughly. (Bugs)
Yes a SSteel panel with washers and either self tapping screws or a ring of metal that is tapped fop screws on the inside (2 half rings) attached by screws to hold it in place when cover is off. good luck olewill
 
I think the plate idea with self tappers & diesel resistant sealant sounds the best solution for me.
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On reflection the sealant might not be such a smart idea unless you can be certain that it does not squeeze into the tank and odd bits end up causing blockages.

A diesel resistant joint washer would be preferable. Nitrile rubber is, I believe, the correct material but check.
 
Can't remember the name of diesel proof gasket, from Beldam Lascar seals. If you want to fit an internal backing plate, cut a rectangular hole. Captive nuts, obviously.
 
I would also recommend a metal plate/self tappers but would use HYLOMAR as a sealing compound. So long as the plate has a reasonable overlap over the hole this stuff wont 'fall' into the tank.

My experience with a nitrile rubber joint was that the self tappers would start to lose grip in the relatively thin plastic before you could get the joint tight enough. HYLOMAR got over the weeping joint problem.
 
The tank is almost certainly polyethylene. Nothing will stick to it - no sealer, no adhesive. Manufacturers often warn you about this when you buy a polyethylene tank. They tell you not to cut holes in your new tank.

You will need to make a mechanical seal. If there is adequate wall thickness to take a self tapper it might work. You need to get sufficient pressure on a dry rubber gasket to get a satisfactory seal. Self tappers in a thin material might not achieve this.

I suppose you could make the small hole into a large rectangular hole and fit a metal plate over it. The metal plate would have an inspection hatch built into it so you could access the inside so you could use nuts and bolts to secure it onto a rubber gasket.
 
I would be very reluctant to enlarge the hole! If you make 2 half rings fitted with captive bolts they can be fitted inside so the bolts come through drilled holes. You can then bolt a cover and gasket on from the outside. Much more secure than self-tappers.
 
Salty John said:
The tank is almost certainly polyethylene. Nothing will stick to it - no sealer, no adhesive. Manufacturers often warn you about this when you buy a polyethylene tank. They tell you not to cut holes in your new tank.

You will need to make a mechanical seal. If there is adequate wall thickness to take a self tapper it might work. You need to get sufficient pressure on a dry rubber gasket to get a satisfactory seal. Self tappers in a thin material might not achieve this.

I suppose you could make the small hole into a large rectangular hole and fit a metal plate over it. The metal plate would have an inspection hatch built into it so you could access the inside so you could use nuts and bolts to secure it onto a rubber gasket.
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I've had a similar problem re-sealing an existing fuel return access fitting in the top of a polyethylene diesel tank. It was removed to drain the tank after water got in via the deck filler. (Don't ask, wasn't me!) Now nearly two years on and at least six goes at resealing it, both by me and by my engineer. I spoke to Tek-tanks and they said that if a nitrile rubber washer didn't work to try an adhesive called INNOTEC: I have bought a tube but not used it yet as the last go with Loctite gasket stuff has the leak down to a minute weep, which I'm reluctant to disturb in case I make it worse again.
 
I have repaired pe tanks in cars and bikes using a soldering iron but the holes were smaller than 35 mm. Find a bit of excess tank material, generally I cut off a bit of the plastic mounting lug and use this as a plug. Then use the soldering iron to melt the edge of the plug into the edge of the hole. You have to push the molten tank material into the hole but hold the plug to make sure it doesn't drop in. There is also a plastic fuel tank repair putty sold in auto shops but I have never had much luck with this. the putty tends to loose adhesion after a year or so.
 
My word ...... What a mass of ideas you are all giving me !!

Salty John's info on non adhesion to Polyurethane is most useful. I am now inclining to the idea of captive bolts on half rings (or rectangles) using metal plates so I could then use Hylomar or maybe Loctite Instant Gasket. Continuing on this theme I could maybe still use the original Mikuni standpipe (or a new one at £12)
The standpipe was obviously meant to be installed thro a tank inspection hatch. It consists of a pipe assembly brazed to an arbor. The arbor which is a turned component has a wide flange perhaps 40mm dia which compresses a nitrile rubber gasket inside the tank, then a 15mm dia threaded part which pokes thro the tank & receives a thick 40mm dia washer & nut. The boat builders "Bodge" was to cut 2 diametrically opposite flats from the inner flange so the assembly could be forced into the tank from outside with just enough of the flange left to hook the 30-35dia hole, then a gasket from some thick rubber material clamped under the outside washer & nut. It was never going to work !! especially when the tank was filled to the deck filler cap as you do. Fortunately the tank is situated in a fibreglass moulded bund so the diesel did not leak into the bilges.

Thanks again for your continued help. YBW is a most marvellous resource.
 
I think you need to make a mechanical repair, something like this:
tankrepair.jpg
 
Tip. If you use the 1/2 plate and stud system,superoir method, make one stud in each 1/2 long a bit longer. makes fitting and removal a simple job. fiddle lower plate into positon put nut on short stud. ditto other half. fit joint and top plate fit nut on long stud then allow to drop remove short nut,tighten long stud,put put on short nut and finish job as normal. :)
 
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