Diesel tank repair advice please

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chas

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I have had a leak in my diesl tank all season - not much - about a pint a week and a bit more if it was rough. The tank is mild steel, about 45 gallons, 30 years old and is under the cockpit locker. The problem is that, although I can manoeuver it in the locker, it is too big to come out through the lid.

I have now found the leak - the tank itself is in amazingly good condition both inside and out. It looks to me as if the leak was caused by an imperfection in the steel rather than rusting through. I have cleaned it back to good metal and now have a small slit about 1/2 inch long and 1/4 inch wide.

Obviously, it would help if I could repair it. Can it be welded? it is surrounded by glassfibre and is a diesel tank. Is there any propriety filler I could use and perhaps glass in the repair? Any advice would be welcome.

Another thing - when I took the inspection cover off, it was sealed in with a cork gasket. What should I use to seal it back?

Thanks for any help

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If you can weld it then do so however there are several things to do before trying to blow yourself up. Thoroughly clean it out to remove as much diesel, residue and fumes as posible and before welding (on the outside) fill it with water almost to the point of the hole. I would prefer to use a stick welder with rods especially for overhead welding if it's on the side or bottom rather than a flame or wire and surround the area with protection for any grp that also will not burn easily.
Once water is drained and tank dry the gasket you can be remade using cork obtained from an auto shop or buy a suitable mastic but put tiny 2 or 3mm washers on the screws between underside of cover and tank top to maintain a serviceable amount of sealer.
Obviously welding is at your risk not mine but I've done it like this before and never come to any harm. Just be sensible.

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Mild steel is straight forward to weld if you have access to a MIG welder. (and someone to do it!) I assume the tank is cleaned out, and the problem area grinded out. To avoid any chance of explotion, fill the tank with the inert gas (Turn of the wire and press the trigger of the welding gun for a period ) The welding itself is no problem (as long as you are a skilled welder...) Take care that nothing on the outside of the tank can catch fire, especially if there are any traces of diesel!!!!!!! Take care and paint it outside after sanding, to avoid new rust. Trying to repair this by any miracle formula is simply waste of good money.
Instead of cork gasket, simply use one of those liquid ones, but let it partly harden before applying too much pressure on the inspecton cover.
Good luck.

<hr width=100% size=1>Knut
 
Sounds as though that you have suffered a stress fracture, I would reccomend that if at all possible, to weld a stiffener across the affected side.

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Lower tank level to allow a safe repair. Clean surface of the cracked area back to shiny metal. check the extremity of the cracks (both ends) they will often extend farther that you will be able to see. Drill a couple of one eigth holes to stop the crack progressing further( one either end). Drill and tap ( or PK screw) a plate over the whole of the area, to cover the site by at least one inch from the crack length and width and clean the plate back to shiny metal, fit together using a propriety gasket paper and sealant, making sure to fit the paper tight around the bolts/ screws.

Any further trouble later on you can empty the tank of diesel (I presume that it is a diesel tank) and fill it with exhaust fumes from a generator or similar and weld the plate on as well. ensure that a bolt is placed either side of a point where any crack could continue along to, so that some support is offered to any weakness that has or may prevail.

I am afraid that when you start to investigate further you may find that a larger area is at fault than you have first believed, if so make a larger patch. :o))

Regards
Rom

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I would advise caution before attempting any welding, to be totally safe you have to degass the tank to prevent an explosion, inerting by squirting in Argon or filling with exhaust fumes will be hit or miss unless you have an instrument that will monitor the tank atmosphere, without this a cold repair is by far the safest.

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Absolutely agree with Mike.... Welding a tank, even a diesel tank is a specialist job, and very dangerous if attempted by someone without all the right kit...

Also, having been on the wrong end of this mistake... do yourself a favour, and use a cork seal, not instant gasket/seal.... these often contain silicon, and if any gets in the fuel, it causes chaos with the pumps and filters.....

A good quality motor specialist will be able to supply you with cork sheets, or if you are really lucky, will have a range of gaskets, with one the appropriate size.... on older cars, they were the standard way of sealing the sender unit into the tank, so they do exist... you did of course keep the old gasket as a template didn't you /forums/images/icons/wink.gif!

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Good point re Paper I would suggest that as I said a propriety "paper" and "sealer" be used the modern ones now available for use with fuels are much better than cork (which the Romans sealed their drains with :o))) and with regard to using exhaust gas as an inert medium it need some compitence/capability to do this.
Rob

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I have used glass fibere and resin to repair a diesel tank leak and it is still holding , it says on the tin petrol and diesel resistant. With such a small hole as long as you build up a few layers of matting it should provide a quick and easy repair. No doubt there will be some reason why it should not be used though.

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"Trying to repair this by any miracle formula is simply waste of good money.

100% agreement. Petweld and other tank sealing systems are in my experience a waste of money, particularly with diesel tanks. I have a slight leak from a small spot on my old Landrover diesel tank - I've tried all sorts to put it right - petseal, epoxy - chemical metal - some webbing stuff I can't remember the name of...
forget it ....
Welding may well work - but whilst a small drip of fuel on my drive is annoying, the mere thought of a fuel leak on my boat would make me want to be ABSOLUTELY sure the tank was sound.


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You shopuld try epoxy and glass as already suggested. The trick is in getting the surface clean and in giving enough layers of glass to make the patch quite robust. Here in oz the Airforce have used epoxy with reinforcing in this case boron strands but also carbon to put repair patches on the wings of Hercules transports and supersonic F111 fighter bombers (over fatigue cracks)with amazing success. The whole trick is in the aluminium surface preparation. will

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Hi William !
Are they really putting "stuck on patches" over stress cracks on transport and fighter plane wings? If so it sounds like you like us are becoming a third world country like us,
Rob

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As an alternative to welding...

A proper welded repair may well be the best solution, but it's probably not a DIY job and it would involve quite a lot of preparation. Epoxy patches might work, but tank sides tend to flex a bit and the patch might not stay stuck.

Several people have suggested bolting on a patch, but this involves drilling more holes, which I'd try to avoid. As an alternative, had you thought of using the slit itself as the fixing hole for a patch? If you put a 6mm SS bolt through it, with a 50mm SS washer and a gasket on each side, using proprietary diesel-resistant sealant on both sides, and tightened it up well, you ought to have a leak-free repair which will cope with the slight flexing of the tank side. This is relatively quick and simple, and could save you a lot of expense.

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Many thanks for all the advice. I must admit that i would prefer a solution that did not involve welding as I could then do it myself. so a patch or gunge of some description would be my choice but I do hear what is being said about the gunge way. Perhaps I will have a chat with a couple of local welders. To really clean out the tank will be a pig, though.

Thanks again - much food for thought.

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Re: As an alternative to welding...

Thanks - the hole is actually in the nbottom of the tank, about an inch from the edge - It would be worth a try.

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I am not sure. It looked as if somene had perhaps dropped a cold chisel or similar on the tank - must have been during its construction or fitting as it is on the bottom of the tank and under the paint! It may well be that the paint is all that held the diesel in for the first 30 years! The metal around is sound ad does not seem to bee very rusty.

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