fuel tank caution - what caused the leak?

Elessar

Elessar

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I've started a new thread on this even though its at the bottom of another because there is a good bit of info to beware of.

I took both tanks out because of a leak.

Sbd tank - looks OK on the outside - can't really see inside. Not leaking.
Port tank - little bit of pinholing outside, but on cutting the bottom off the inside was cratered like the surface of the moon.
BD marine showed me something in the port tank that made me happy that the Sbd tank will be OK without cutting it up to inspect inside.

Can you deduce or guess what it was?
 
Something made of Stainless Steel?
Part of a filler cap or jubilee clip etc. dropped in there?
 
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Aluminium tanks, when you have a bit of the diesel bug their excretia is acidic and it is this and a bit of water in the bottom of the tank that corrodes it away.

The best I have seen is at only four years old.
 
In my Merc Diesel workshop manual, it says to drain and clean the fuel tanks every 5 years, I guess as a precaution to the issue you have raised. I have owned the boat for a couple of years, and am guessing that this has not been done, so will think about "another Winter job".
 
There must have been water there for there to have been any such effect; a good reason for using blow moulded HDPE tanks, rather than (any) metal tanks for fuel.

Graham
 
The fact that you get moisture between the bottom of the tank and the grp moulding they sit on doesnt help, theres no ventilation and the s/s water tank was touching the fuel tanks on the boat I changed all 3 tanks on, only one was leaking but the other two were on borrowed time so I decided for the work involved to remove the one it was best to do them all at once.
 
Forgive my ignorance (again please!). I understood that 'plastic tanks' didn't like petrol because of the ether in the petrol, are HDPE tanks affected the same way? The reason I am asking is that I have to get new tanks for my (petrol) engines and am unsure of the best material to have them made of. I had thought of stainless steel and fitted with rubber around all edges and corners to stop 'chaffing'
 
mil1194 said:
Forgive my ignorance (again please!). I understood that 'plastic tanks' didn't like petrol because of the ether in the petrol, are HDPE tanks affected the same way? The reason I am asking is that I have to get new tanks for my (petrol) engines and am unsure of the best material to have them made of. I had thought of stainless steel and fitted with rubber around all edges and corners to stop 'chaffing'
Click to expand...

Almost all new cars have used blow moulded plastic fuel tanks for a number of years now; sometimes they are multilayer, to reduce permeability. Outboard tanks ar plastic as well. The petrol tank on my 2004 boat (an American boat) is blow moulded HDPE, as was the one on my previous boat, dating from 1999. The disadvantage is that they are only available in certain shapes, generally rectangular and there's no way to custom fabricate them from sheet. I've got the name of the tank manufacturer somewhere, I'll try to find it; their website may give you an idea of what is available.

Graham
 
Slight correction; the plastic tank on my boat is a rotationally moulded part, rather than blow moulded (tooling for blow moulding would be too expensive for marine volumes), also it is cross linked HDPE, not HDPE.

The manufacturer is Moeller Marine; they have an enormous range of shapes and capacities available; see their website for both aftermarket and OEM tank details. I don't know if they have a distributor in Europe though, you might have to import one from the US (iBoats, Cabelas, Boaters World stock them and all will export to the UK).

Tek-Tanks in the UK also carry a range of fuel tanks suitable for petrol, the maximum volume is lower and the range of sizes more limited though.

Graham
 
Elessar said:
I've started a new thread on this even though its at the bottom of another because there is a good bit of info to beware of.

I took both tanks out because of a leak.

Sbd tank - looks OK on the outside - can't really see inside. Not leaking.
Port tank - little bit of pinholing outside, but on cutting the bottom off the inside was cratered like the surface of the moon.
BD marine showed me something in the port tank that made me happy that the Sbd tank will be OK without cutting it up to inspect inside.

Can you deduce or guess what it was?
Click to expand...

Steam clean it and weld on a new aluminium 5 mm base.
Job done, you know it fits along with all the fittings.

Plastic is great for new installations but you are going to a heap of hassle and there are hidden issues like, when you drill the holes for the sender etc plastic drill fragments may block your pick up.
 
The aftermarket Moeller tanks seem to come with the necessary bits ( pick -up, fuel level sender) already installed.

Graham
 
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One option to prevent this is to use steel tanks and coat them, most tanks are mild steel, stainless steel, or aluminium; you simply have the tank manufactured or buy a standard tank and ensure it has a good access. Coat inside liberally with a suitable epoxy compound and apply several thin coats or a couple of thick coats.

This should be allowed to fully cure before use, ensure the epoxy is suitable for coating fuel tanks as there are more variations than flies round a dead dog, and take the time to do the job properly. On used tanks it means a thorough clean and scouring the surface to bare metal.
 
DAKA said:
Steam clean it and weld on a new aluminium 5 mm base.
Job done, you know it fits along with all the fittings.
.
Click to expand...

that's what BD marine did for me.

It's now back in, furnature reinstalled, floor panels sikaflexed back in.

I hate to think what this job would have cost if I'd charged myself for it!
 
Aluminium & Stainless Tanks

As a marine tank manufacturer I would recommend aluminium, the secret is in the grade that you use and the shape. The worst thing that you can do, as has been mentioned is to let the tank sit in salt water.
For a rib with an underfloor tank you can use ally if it is powder coated or well painted and then back filled with two pot foam.
Always ensure for any other tank that the mount is well drained and flat, clean it before installation a stray screw can cause havoc in time. Strap down with either webbing ratchet straps or stainless bands with rubber under. Make sure that the tank is well earthed.
If you go the plastic route make sue that the material is suitable for the fuel; petrol has more aditives in now that can eat into the wrong materials, similarly with moulded GRP tanks; old boats are having problems with this.
An ally tank that is well fitted will last at least 20 years, we have 33,000 produced that prove it !
 
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