Fuel tank leak

[donm]

My fuel tank is deep in the bilges and I have long suspected that it has a very, very small leak as there always seemed to be barely visible "snail trail" from the tank. It is between two full depth floors so you cannot see any of the tank other than the top - so I bit the bullet and took the tank out, stood it up on the bench, added a quarter fill of fuel and waited ............................. After a day nothing showed up so I picked off one scab that looked like a rust blister (but the tank is aluminium!) and hey presto, there is a tiny pin hole leaking fuel out. And I mean tiny, as although it leaks it can easily be stopped with said pin. I guess that with more head of fuel the "blister" was leaking out.

Don't know why/how the hole is there as the aluminium looks fine and the tank is suspended and does not touch anything. Anyone any ideas?

As the hole is so small (and unless I find more holes) I thought to plug it with a small bolt and two rubber washers and paint the whole tank with a bitumen based paint or similar?

 

[vyv_cox]

That is the repair method I would use.

It is difficult to get a paint to adhere to bare aluminium. An etch primer bonds to the aluminium and provides a good base for whatever paint is chosen. Perhaps the easiest is an aerosol of automotive etch primer but Hammerite special metals works very well indeed. Personally I would not use a bitumen based paint, any decent alkyd type should be fine.

 

[donm]

That is the repair method I would use.

It is difficult to get a paint to adhere to bare aluminium. An etch primer bonds to the aluminium and provides a good base for whatever paint is chosen. Perhaps the easiest is an aerosol of automotive etch primer but Hammerite special metals works very well indeed. Personally I would not use a bitumen based paint, any decent alkyd type should be fine.

I'm pretty sure that what is on there now is Hammerite Special if I remember correctly - I had the tank out about 10 years ago to cut an access hatch in it. I was thinking bitumen so as to build up a membrane to cover any imperfections that cannot be seen?

 

[Boathook]

Is it worth removing all the paint on the outside of the tank to check it out ?

If one hole has appeared maybe more are on their way ?

 

[penberth3]

I'm pretty sure that what is on there now is Hammerite Special if I remember correctly - I had the tank out about 10 years ago to cut an access hatch in it. I was thinking bitumen so as to build up a membrane to cover any imperfections that cannot be seen?

Wouldn't diesel dissolve a bitumen coating? I've successfully used araldite to seal pin holes.

 

[mjcp]

Curious that you have "rust" issues on an Ali tank...

Is it possible its NOT ali?

Looking at the surface pictures, there appears to be other "bits of rust" - the odd bits that are proud of the surface paint etc.

Possibly there was some grinding (of iron / steel) going on in the vicinity of the bare tank and there's some dissimilar metal nonsense going on under the paint?

 

[penberth3]

Curious that you have "rust" issues on an Ali tank...

Is it possible its NOT ali?

Looking at the surface pictures, there appears to be other "bits of rust" - the odd bits that are proud of the surface paint etc.

Possibly there was some grinding (of iron / steel) going on in the vicinity of the bare tank and there's some dissimilar metal nonsense going on under the paint?

Yes, that's what I thought. Some steel touching the tank.

 

[Freebee]

I had an aluminium tank in my car, due to it standing about in store for 3 years - condensation had built up inside the tank causing the steel fuel pump and level gauge to go very rusty inside the tank. over time this rust flaked off and sat in the bottom of the tank and corroded the tank in small spots from the inside out causing the tank to become porous with many tiny pinholes. I wonder if you have a bit of the same happening in which case this could be the one and only hole or the beginning of a lot of them ....If it was me I would be looking inside to see what is happening.

Bitumen paint will be fuel; soluble .. If you want to seal JB weld is made for this job- amazon -

J-B Weld 2110 Metal Fuel Tank Repair Kit,​

of course there are other suppliers !

 

[KompetentKrew]

That tank looks like mild steel to me.

Even the welding at the top has that look to it.

Have you checked with a magnet, please?

 

[geem]

That tank looks like mild steel to me.

Even the welding at the top has that look to it.

Have you checked with a magnet, please?

There does seem to be what looks like rust patches on thr bottom welds

 

[BobnLesley]

I can - based on first hand experience - concur with Freebee's JB Weld suggestion. I don't recall the specific make, but I used epoxy-metal to repair four pin-hole leaks in a s/steel tank while in Curacao and they were all still diesel-tight when we got to New Zealand three years later.

 

[Plum]

Is it worth removing all the paint on the outside of the tank to check it out ?

If one hole has appeared maybe more are on their way ?

Very sound advice and based on the signs of some more rust in other areas in the photos (which suggests this is a steel tank) and that it is impossible to inspect or paint in situ I would consider getting a new tank made from a material that does not rely on a paint film.

 

[donm]

There does seem to be what looks like rust patches on thr bottom welds

It is aluminium and no steel fittings inside, outsde or touching it.

 

[Boathook]

It is aluminium and no steel fittings inside, outsde or touching it.

Wondering why it has been painted. What are the brown stains by the welds ?

 

[donm]

Wondering why it has been painted. What are the brown stains by the welds ?

Wondering why it has been painted. What are the brown stains by the welds ?

I took it out about 10 years ago and cut a hatch opening for cleaning - which is how I know that it’s aluminium. Brown staining below the pinhole is most likely caused by several years of diesel quietly leaking out

 

[donm]

That tank looks like mild steel to me.

Even the welding at the top has that look to it.

Have you checked with a magnet, please?

No, but I did cut a big hole in the top for an inspection hatch. It’s aluminium

 

[donm]

No, but I did cut a big hole in the top for an inspection hatch. It’s aluminium

The brown that you can see at the bottom of the tank below the weld is some cardboard that it’s resting on to prevent staining the bench. Sorry if it has misled anyone