Welding a leaky diesel fuel tank

I echo those who say that if you've found some pinholes, many more will follow. My tank went west very rapidly after the initial weep started! If you can get to them, I'd recommend West of Scotland Engineering for making a copy of the existing tank. They did an excellent job in very limited time; we needed it done by the end of the week we took it to them, and they delivered a day early. They would have powder coated it, but pressure of time meant that we ended up painting it ourselves. The price was not too bad as well. The tank fitted the existing mounting points precisely; every bolt went through without any fiddling.
 
Aluminium can be either TIG or MIG welded. Re-welding all the existing welds would probably do the job. I agree that with mild steel, once the corrosion starts, it's probably uniform including the plate, but this is less true of both stainless and aluminium.
If you can see inside, inspect carefully, visually. See any pitting? If so then you might have a bigger problem and need replacement. If the sheeting looks good internally and externally and all you see is welds that are suspect then re-welding seems sensible. On a used tank, any coating thoughts are a bit over-optimistic.
 
It is clear that a re-weld/patch weld will not be a good option as you can see from many of the anecdotes in this thread. Patching an old leaky metal tank like sweeping the dust under the bed, no sooner will it come out again and typically when you are least prepared.
Your best and most reliable option it to begin thinking about how to get a new tank and this option can be approached be two ways:
First, find a new tank that can fit your lazarette , maybe a smaller sized one if need be. Many marine catalogues carry a wide array of tank shapes n sizes and I find it very hard to believe that’s you will not find something out there that can fit.
Second option is adjust or modify your lazarette to be able to accommodate the standard tank sizes out there.
 
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As a licensed tanks inspector (API, STI, DOT), I can tell you with some certainty that unless you have done an internal visual or at least comprehensive UT, you have no idea what the nature of the corrosion is. Could be general, but pitting under sludge deposited is more common. You have no idea if you are welding to good metal or to thin or porous metal.

Thus, there are three choices. Roll the dice and do anything you like, clean the tank perfectly and give it a real inspection before you start, or replace it. Remember also that a leak test only says it's not leaking right now. It doesn't tell you anything about 10 days from now. And don't test at more than 5 psi unless you want to crack a weld.

It would probably be cheaper to replace than to do it right.
 
Did have a alloy petrol fuel tank repaired ages ago.
Loads of grief cutting it out complete and whole from floor.
Contacted a few outfits who refused to even look at it.
Eventually a formula four car builder just round the corner on our industrial estate said bring it round for quick look.
Bottom of the tank was mass of pin holes.
They simply welded a new "tray " onto the bottom coming up about "6" up the sides of the tank welding onto pristine metal.
 
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oldgit said:
Did have a alloy petrol fuel tank repaired ages ago.
Loads of grief cutting it out complete and whole from floor.
Contacted a few outfits who refused to even look at it.
Eventually a formula four car builder just round the corner on our industrial estate said bring it round for quick look.
Bottom of the tank was mass of pin holes.
They simply welded a new "tray " onto the bottom coming up about "6" up the sides of the tank welding onto pristine metal.
Click to expand...

You forgot to say - did it work medium/long term?

- W
 
I know people who have had petrol tanks welded for old competition motorbikes.
It's usually a repair that lasts long term.
The problems are usually related to corrosion from dissimilar metals around mountings and vibration.
As thinwater says, the problem in a diesel tank is likely from water-bearing sludge at the bottom, so cutting out the whole floor and replacing with new metal might be worth considering.
But it's possible the problem is really (or partly) that the metal tank has been sat in a puddle of salty water for n years? Does it just sit on a flat grp board by any chance?
 
.
The problem is with a new patch that has been welded in and seems to come from corrosion on the outside caused by leaking diesel (from a dodgy fitting) running down the weld. My man in the wilds of Argyll reckons he can cut out and patch the affected weld. I will then etch-prime any bare aluminium and apply several coats of some sort of wonderpaint.

Hopefully by the time it goes again I will be able to contemplate having a tank made.

- W
 
Regardless of which welding technique is used the thing has to be washed out & purged first, The risk of explosion is very high, & if the metal is at all porous will still sweat diesel fumes. I well remember being asked to weld a large silencer up at a boatyard in Old leigh, the heat from the torch caused the old oil inside to gas off, thick white smoke started gushing from the end, i stepped back & the thing took a mighty toke of air inwards. This was followed by a large explosion that burst the seam on the silencer & rendered me deaf for some time. Fuel tanks will do this as well & can cause serious injury or worse. Probably explains why many people dont like repairing them!
 
webcraft said:
You forgot to say - did it work medium/long term?

- W
Click to expand...


Certainly lasted for the next year or two when the evil heap money pit was eventually sold on to couple of blokes from Essex, when I finally lost patience and confidence in the two "Black Anchors" (Mercruiser outdrives) hanging off the back of the boat .
Think the two blokes then started UKIP to get their revenge on the world. :)
 
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Have a look at POR 15, you'll have to decide for yourself if you think its good for ally. I've used it successfully on a stainless fuel tank with a leaky weld and its lasted 4 years so far, mainly because the tank wasnt easily removable - since yours is out it may be easier to apply.
 
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