Identified a small leak from my fuel tank today. About 1 drip per 2 minutes and leaves a small puddle on the floor overnight.

I've pretty much identified where its coming from although I can't see if its a pinhole or a hairline crack. Seems to be coming from the weld on one of the corners. Photo attached. Reference the green marks I drew the leak appears to start about 2cm below and travels both directions (slightly shaded patch in the photo and just as hard to see in real life. You can ignore the scratch next to the green line as that was me marking before I found my green pen. There is a mark made by handbrake cable further down which I thought was the cause but the leak actually starts about this mark so its not that. But other than these two there's no obvious marks. It must have happened relatively recently because I noticed the smell in the garage.

Access is a little difficult for welding, tank is silkoflexed to the chassis and I shudder to think what kind of precautions need doing before welding a petrol tank anyway. Would epoxy JB weld or similar be fuel resistant enough to deal with a small leak?

That looks almost identical to a leak I had, who made it and when?

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Originally posted by Doctor Derek Doctors
That looks almost identical to a leak I had, who made it and when?

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Who stuck it to the chassis?

Stupid idea that is imo!

Welding is no issue,if you could get the tank out that is!

My m8''s welded loads of alloy tanks, just leave them to dry out for a while before welding and they are fine.
Welding is the only 'proper' fix

Many many years ago I grounded an overloaded A30 on a curb and knocked the tank drain plug causing a leak. I drained, cleaned and applied a large blob of epoxy putty - I can't remember the name of the stuff but it came in 2 tins, 2 different colour putties that you mixed together in equal quantities. It never leaked again.

I have used Granville Petro Patch Putty to seal a leaking motor bike ally tank with success.The area needs to be clinically clean
and abraded. https://www.amazon.co.uk/Granville-0455-Petro-Patch-Putty/dp/B004OS8N1W
Bonding the tank to the chassis!!!!!!!! Why?

Granville Petro patch putty is what I used on my fuel tank and its not leaked for over 2 years.

POR-15 do a liquid that you pour in the tank and sloosh around. I have no experience of this stuff, so I can't comment on how good it is, but I expect it will be expensive...

Another vote for Petro Patch , didn't know it was still available. As others have already asked , why Sikoflex? Suspect the best way to cut it would perhaps be a cheese wire type windscreen remover?

Looking at the etching around the weld it looks like it's been fused rather than adding rod like you usually see on ally work . If it's a crack along the weld with no filler metal rather than a pin hole it's a lot more likely to happen elsewhere if that's how the tanks been welded up . Normally a quality tank has a lovely stack of dimes pattern on any weld Seams

POR15 do a not very expensive tank sealant but you use gravity to get the stuff to the right place which might be tricky... Technoweld would work but would need a big torch with that surface area....

Yeah i initially silkaflexed it to chassis to make sure it wouldn't vibrate but then it stuck so well i didn't need to bolt it down. Maybe not so clever in retrospect. Still i don't think it will be too hard to remove. Was thinking cheese wire method too like rusty nuts suggested. Someone PM'd me a story about that whole weld failing suddenly which sounds rather scary. I'm allergic to fire

Petrol patch will do it but it's not permenant especial if exposed to road grit and water
I used POR 15 and whilst you need to clean and prepare the tank with chemicals that comes with the full kit carefully and dry the tank out completely once you have used the POR 15 it produces a tough fuel proof layer in the tank.
I even used it to line an intake manifold that had bad welding and porous tubes

If you are going to remove the tank get it welded end of!

All these sealers etc are only really acceptable if the tank can not be removed imo

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Originally posted by CosKev3
If you are going to remove the tank get it welded end of!

All these sealers etc are only really acceptable if the tank can not be removed imo

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You could just some of this stuff

http://www.frost.co.uk/oyltite-stik-seals-oil-leaks-thread-sealer.html

The instructions just say you have to vigorously rub your stick into the crack after peeling back the outer coating.

Reminds me of sex ed lessons...