Fuel tank leaks

[dalraidia]

The 75-gallon fuel tank in my Allied Mistress 39 has developed a very slow leak. Like perhaps a drop every few hours or so. I know that the tank has some rust -- it is, after all, 38 years old. And I suppose that at some point, even though I painted as much of the tank as I could reach, a pinhole has developed. The question is what to do about it. Replace the whole tank (major!!)? Some kind of sheathing I can apply? Any ideas will be gratefully received.

John
S/V Dalraidia

[beanctr56]

Whats the tank made of? I had an aluminium tank on my Catalina 28 devlop a pinhole leak. Put alot of fuel in my bilge. One corner of the tank had been sitting in a a very small pool of water for a long time. I replaced it with a SS tank from Catalina.

I think you are going to have to replace it. Maybe have a new one made.

Rick

[deniseO30]

Replace, is it accessible ?

[apogee1mars]

Diesel or gas?

[sailingfool]

I would think you need to plan the replacement of the tank, preferably over the off-season winter. The pinhole will only get bigger, and you wouldn't want a serious leak developing early in a season where the replacement process may lose you use of the boat for a while.

Unless you are very fortunate you will find that the builder did not make any particular arrangement for removing a failing tank...hopefully you wont need to pull the engine...

[RichH]

Black iron tanks, such as found in the Allied Mistress, can be easily repaired by building an epoxy fiberglass liner 'inside' the existing tank, using the existing tank as the 'mold' for the fiberglass 'liner'.
For such a rebuild, you will need to cut large access holes in the top that are 'wide enough' to get inside to: extract the built-up gums and biological deposits (WEST recommends using garage floor 'degreasers' that 'absorb' the oil, etc.), then surface sanding/grinding to get the metal back to bright and with a significant amount of 'tooth' or surface roughness to the base metal. Then several layers of 4" wide FRG tape is applied across all weld zones (to reinforce the 'usual' places of leakage), followed by applying cloth to build up to ~3/16"-1/4" thick FRG for a nominal 100 gal tank and finishing with a resin-rich application. The large access holes can be closed using large (11 gage, etc.) plates that are applied to a 'studded' closure configuration (bolts affixed to the underside of the 'cut' and penetrating through the old tank wall ... you can do all of this 'sistering' by using a portable drill - drill, tap, screw-in, etc. simultaneous through the new access plate cover and the edges of the old tank). Gasketing for the new closures should be precut 'strips' of neoprene/Buna and can be obtained from the usual online industrial supply websites, then caulked/sealed with fuel compatible caulk or 'gasket compound' (Permatex).
Such is almost as durable as a new tank, doesnt require the removal of the old tank, and is vastly cheaper (your time is 'free') than a new tank. Only special consideration is that the liner be completely free of pin holes, etc. as fuel (& water and microorganisms) leaking between the FRG and the old tank walls will 'accelerate' any corrosion. Some tank builders will use a 'spark test' to validate the integrity of any installed 'liner'.

The WEST SYSTEM 'projects' website has quite a few 'fuel tank liners' illustrated and explained. Such 'FRG liners' should NOT be used for water tanks ... due to the organic emissions from the FRG.

hope this helps.

[Cptken]

No experience with this but there are good testamonials on the web.

J-B Weld Company - WATER WELD Product Information

If it were my boat, I'd replace the tank if possible. If there is one hole, there will probably be more.

[tommays]

I just started with my third tank in 41 years

[Yorksailor]

Cut a hole in the top and put in a fuel bladder. A days work rather than a week or more.

Marine Fuel Bladders and Auxiliary Fuel Tanks or similar

Phil

[apogee1mars]

Originally Posted by Yorksailor

Cut a hole in the top and put in a fuel bladder. A days work rather than a week or more.

Marine Fuel Bladders and Auxiliary Fuel Tanks or similar

Phil

Good advise. I like the idea of using the old tank as armor.