Hypothetical question ref leaking diesel tank (may be a real question):(

RobWales

RobWales

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www.3ksengineering.com
Hi all,

I suspect that the diesel fuel tank might be leaking (yet to be proven)on my Fairline sprint mobo!

The tank which is aluminium and full width of the boat sits within a dedicated compartment and has approx 1/2 inch clearance all around to each bulkhead, I have noticed diesel sitting in this void space and cannot see any leak paths from the only connections which are on top...i.e filler,supply,return,vent and level sender.

I aim to fully investigate the causes at the weekend...?

However as a pre thought to a remedy, removal of the tank is going to cause me to have to cut the pre moulded deck sections away at each end, as it seems the tank was fitted prior to the moulded deck being bonded in place this I would prefer not to have to do!

So a bit of lateral thinking here and please chip in with suggestions...

What if I were to drain the tank and the void space and then fill the void space with a medium of sorts...i.e closed cell polyurethane foam injected in? or some form of resin poured in....in the hope that this would then seal from the outside?

The total amount of "medium" required would not be a vast amount to fill the void space so I'm certainly not worried that its going to add weight!

And if the said medium is filled up to the top face of the outside of tank then can it leak any further above this point?

Maybe I'm being deluded but what does the panel think?

Thanks in advacnce.
 
sealing tank on outside

Just a thought, but if you fill the void you will still have the tank leak, the leak path may change but it will find its way out, and if the leak is from a cracked tank it will only get worse, and then you may have to replace the tank but now having the added problem of removing the foam or resin first, you might be better off finding the leak. you could empty the tank, pressure with air and use soap/water on the outside to find the leak?
 
europe172 said:
Just a thought, but if you fill the void you will still have the tank leak, the leak path may change but it will find its way out, and if the leak is from a cracked tank it will only get worse, and then you may have to replace the tank but now having the added problem of removing the foam or resin first, you might be better off finding the leak. you could empty the tank, pressure with air and use soap/water on the outside to find the leak?
Click to expand...

Yes but in finding the any leak I will have to remove it to repair and thats the last thing I want to have to do!
 
one of the issues is that of resin / foam possibly heating up during the curing process. Could be embarassing.

Also, if the leak is at the bottom, how are you going to ensure that your mixture completely fills the void ? And if you overfill, the pressure on one face could well split an aluminium wall of the tank.

Sorry, snags but no solutions.
 
The tank has probably corroded at the bottom poss due to sitting on damp wood stringers.
One way or the other it will be coming out to be fixed.You can throw as much time money and neat ideas at it as you want,,,,but out it is going to come.
Either new tank or in my case complete new sheet welded on bottom of tank to cover a myriad of pin holes and latent pins holes just waiting to leak.
Probably best to post this on MoBo chat be amazed if somebody has not been here before.
Due to stupid stupid boat design we had to grind out deck above tank in order to remove and repair.Did not bond deck back but arranged fixings in order to get at tank and bilges should need arise in future.
Only other option is to drop slightly smaller tank insdie original but the deck will still have to come up.
 
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sarabande said:
one of the issues is that of resin / foam possibly heating up during the curing process. Could be embarassing.

Also, if the leak is at the bottom, how are you going to ensure that your mixture completely fills the void ? And if you overfill, the pressure on one face could well split an aluminium wall of the tank.

Sorry, snags but no solutions.
Click to expand...

Have done some research on the expanding foam, does not give off too much heat and you can get a slow expanding type which is used to creep up cavity wall cavities! so maybe we do not seal the exact spot with it but we do seal the whole area above and around the tank...so no more leak? other than what sits under tank in its dedicated space??
 
RobWales said:
Have done some research on the expanding foam, does not give off too much heat and you can get a slow expanding type which is used to creep up cavity wall cavities! so maybe we do not seal the exact spot with it but we do seal the whole area above and around the tank...so no more leak? other than what sits under tank in its dedicated space??
Click to expand...




The fumes are going to come out somewhere eventually and pong like hell ?
 
RobWales said:
Have done some research on the expanding foam, does not give off too much heat and you can get a slow expanding type which is used to creep up cavity wall cavities! so maybe we do not seal the exact spot with it but we do seal the whole area above and around the tank...so no more leak? other than what sits under tank in its dedicated space??
Click to expand...

Is the "dedicated space" coated in GRP and diesel-proof? Presumably it is otherwise you'd have diesel in the bilge by now. I reckon you could bodge it, rather than take the tank out, but I'd go for a different approach. If you fill the entire space around the tank with foam or resin, it'll make life difficult if you do have to remove the tank eventually. I'd be tempted to jam some foam strips into the gap, at the top of the tank, so that they're more or less level with the top of the tank, then apply some GRP over the strips and on to the edges of the top of the tank. This should seal the voids to stop diesel smells in the boat, and if you do have to remove the tank one day you'll only need to cut through a thin strip of GRP first.
 
It's a long shot but...... I was convinced that I had a leaking fuel tank. What else could it be when I filled the tank and over several days it emptied into the bilge. Must be a leak.

By chance, I discovered a pin-prick hole in the fuel take-off pipe.
It's a one in a million chance but worth a look. And it won't be obvious at first sight.
 
If the leak is in a place you cannot see then there will diesel around that spot on the tank. Surrounding it with foam is unlikely to work as the foam will not stick to the diesel covered areas.
 
How about cutting the top off the old tank (Danger - fire!) if you can get access then fitting a new one inside the old one? Or can you empty it and pour something into it to seal the presumed hole? As long as it doesn't reach the injectors!!!
Good Luck.
 
To my mind you have to find the source of the leak. Are you able to pressurise it to check the hoses, etc. Failing that it is a take out job and the work it involves though this is easier than once you have filled voids up with 'foam/filler'.
 
Are you sure you have a leak?, I would mop up whats under the tank and monitor it further, diesel on water (oil) may look excessive but a small amount of oil goes a long way on bilge water.

The only real way of dealing with the problem is to have the tank repaired or replaced, bodging only puts off the enevitable, even if it cured the leak for the time being (which i doubt) it will return when you least want it (mid passage, heavy seas etc).

There is a process called Tank Re-Nu, where the tank is baked and coated with rubber, inside and out, but you still need to be able to remove the tank and courier it to the franchise for it be completed (though it's only half the cost of a new tank).:cool:
 
You first need to prove that it is the actual tank that is leaking. How about sealing all the connections I know this will not be easy maybe a rubber glove over the inlet ?. connect a manometer to one of the connections using a bit of rubber pipe. (If there is diesel in the tank use one that terminates above the diesel level inside), blow a bit of pressure into the tank and see if it can maintain this pressure over a period of time. You can easily make a makeshift manometer with a piece of clear tubing clipped to a piece of wood in a U shape half filled with (I would use diesel so as not to risk getting water in your system). I would have thought around 60 Millibar = (60 CM) would be enough pressure over a 5 minute period.

http://www.machineryspaces.com/pressure-measurement.html

You can blow down the rubber pipe to charge the pressure and then squeeze the rubber pipe whilst you fit it to the manometer (watch you don't over do it or you will loose the diesel in the manometer) :D
You may get a slight change in your reading depending on the temperature of the tank over your test time.
Whilst you are testing you can go around with a leak detection fluid (weak soapy water) and a paint brush to check all your joints.
Good luck
Pete
 
Thanks all,

Pete top of my tank including all connections are bone dry and remain bone dry at the exit point out of the tank space...hence even before I invetigate further i.e. pressure test etc I'm convinced its the tank that's knackered!
Repairing the tank is going to prove no problem as I work for an engineering Co specialising in fabrication etc..
I just was hoping to be get away without having to cut sections out of my deck :(
Tank space is fully gelcoated etc so no matter how much leakage it stays around the tank and goes nowhere, plus the tank space is below the cockpit area and not the cabin so I'm not getting fumes into the cabin!
Just so bloody annoying if I have to damage things which even if done carefully are not to my liking!
Still investigating a "medium" of sorts that can be poured in the void space and allowed to harden....
 
RobWales said:
Still investigating a "medium" of sorts that can be poured in the void space and allowed to harden....
Click to expand...

If diesel can get out of the tank then whatever chemicals you put in the void can get into the diesel and knacker your injectors. The tank rupture won't get better, it will get worse, so another vote for removing the tank top plate and fitting a new poly tank inside.
 
The Lazy Kipper said:
If diesel can get out of the tank then whatever chemicals you put in the void can get into the diesel and knacker your injectors. The tank rupture won't get better, it will get worse, so another vote for removing the tank top plate and fitting a new poly tank inside.
Click to expand...

Diesel being a very light oil will find its way out of the smallest pin hole or seam split yes?

My thought process is based upon a much thicker consistency "medium" which will not find its way back into the tank before setting...then even when it has set I'm not going to be concerned if the hole/split does increase in size!

Though I'm liking the poly infill idea ;)
 
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