Leaky Diesel Fuel Tank - Fix or Replace?

[and4ew]

My planned five-day coastal cruise was cut short when I found that diesel was leaking into my bilge. I checked the hoses and fittings and didn't find any diesel drips, and also the bilge slowly fills even when the engine is not running, so I surmised that the tank itself is leaking.

The tank sits in the bilge, a little off the bottom. It's mounted with fibreglass shims. It's not the original tank but was "custom made" and is stainless steel. It's 70 litres.

I'm guessing that the bottom, sitting so close to the bilge, has corroded. I haven't pulled it out yet as it's more than I could do by myself.

My options are to pull it out, find the leak, and weld. Alternatively, I could just replace it with something like a Moeller Marine fuel tank which are not metal. So my first question is: should I fix or replace?


Second question: the Moellers (and others) I've seen don't seem to have a return for diesel. Would I just add another spigot for that? If so, should it have a hose that goes down into the tank (like the feed-side does)?


Third question: my current tank is 70 litres. That seems like a lot for coastal cruising. I consume 1 litre per hour @ 5 kt and don't have to charge my batteries often. I feel like 30-40 litres would be fine for coastal cruising. Thoughts on this?

[Bowdrie]

Stainless steel has seldom been the best choice for diesel fuel.
In the "old" days of high sulfur fuel, any water in the tank, (which migrates to the tank bottom,) would react with the sulfur, creating sulfuric acid, which attacks the welds.
The stainless is OK,, but when it is welded the welds are susceptible to corrosion from the acid.
Even with todays "Low Sulfur" fuel, welds in stainless are suspect over the long term.
The problem is not made any better by the common use of thin gauge metal,, not much there to work with.
A good sheet metal shop may be able to weld on a new bottom section.
An Aluminum tank is better, and even though it can be attacked, tanks made from it are usually of much thicker material, so they generally can go longer before a failure, but being stuck in a bilge with perhaps its lower section exposed/immersed to salt water won't be so great for it either.
Kind of like being between a rock and a hard place.
You mentioned a Moeller tank, a return might be easily incorporated in the fill hose using some kind of T fitting.
Nothing wrong with a tank made out of fiberglass/epoxy either,, Hatteras and Bertram have been using them for decades without incident.
In a perfect world all of our, (metal,) fuel tanks would be made from Monel,, or Titanium.
If you decide on an aluminum tank you must be absolutely sure that their is ZERO stray currant on any (if used,) bonding system/wires.
An aluminum tank exposed to salt water with some electrical potential will fail in short order.

[MicHughV]

some people will probably find this insane....but I did it anyway.....when I was building my first boat....

I needed a custom diesel tank made as it had to fit in an awkward location. I also didn't have any money to have one built for me. I was 20-something years old and broke.

So I fabricated one from plywood and slathered it inside and out with WEST SYSTEM epoxy...

Yep, I did.....that tank lived happily in the bilge for 10 years....never leaked, broke, or caused any other problems.

It was later replaced with an aluminum tank....but......

[Bowdrie]

Originally Posted by MicHughV

some people will probably find this insane....

I don't find that insane at all.
Even more so if the tank was fiberglassed inside.
The key to making such a tank that will last "forever", (so to speak,) is to fiberglass the various plywood sections BEFORE you assemble the tank, and use an external cleat arrangement to join the parts/panels.
Then, the sections can be put together using a well thickened epoxy "mush" to join the parts.
It's actually a good way to build a custom tank,, holding, and or water tanks can be made that way also.
The Centek company makes all kinds of fiberglass tubes/elbows, etc. out of filament wound fiberglass that are highly suitable for fills/drains/fittings, that are easily incorporated into tank construction.

[zemurray]

I replaced with a new aluminum tank from the manufacturer, it wasn’t that expensive. About $600 if I remember correctly. If you measure your current tank they can make one to the exact specifications. They might even have the original tank design on file if you can find the original tank manufacturer. I’d replace with new. Florida Marine Tanks is who made mine originally and did give me a quote on a new one, but i ended up just buying direct from Tartan.

[Lepke]

Whether you fix your current tank or have another built, apply a diesel tank coating to the inside and the tank will outlast the boat.

[Pete7]

In addition to Bowdrie's excellent comments, stainless steel tanks can flex which just adds to problems on welded seems. Ideally the tank is made by folding a sheet so there are fewer welds, but some are always needed.

Tank needs to come out to see what the problem is.

There is no chance of coating the inside of a stainless steel tank that has been used for diesel. Anything that is painted inside has a risk of coming off and blocking the fuel pick up pipes. Keep the water out and the diesel will look after the stainless steel.

Pete

[Group9]

This happened to us on our last cruise. It was going to be weeks before we could get a replacement, so we pulled it out, covered the thing in West System epoxy and fiberglass reinforcing cloth, and kept going. It still hadn’t leaked a drop when we returned home a year later.

[wsmurdoch]

Originally Posted by Group9

This happened to us on our last cruise. It was going to be weeks before we could get a replacement, so we pulled it out, covered the thing in West System epoxy and fiberglass reinforcing cloth, and kept going. It still hadn’t leaked a drop when we returned home a year later.

We did the same when our aluminum diesel fuel tank began leaking in the Bahamas. When we replaced the tank a year later, we found the repair to still be in perfect condition.

March 18, 2018 https://irish-eyes-to-the-bahamas.blogspot.com/2018/

February 15, 2019 https://irish-eyes-to-the-bahamas.bl...&max-results=7

[MicHughV]

Yes, my tank walls were plywood, but reinforced with 1x2's elsewhere along the outside edges, also fitted a baffle wall inside. The fill connecter was a pvc elbow also glued to the top with WEST, the suction and return lines were copper also glued in with WEST. I rough sanded the copper and surrounded it with a thick cove of WEST with some high build additives. These were located on top of the tank, so leakage was never a concern. The intake line reached down to within an 1" or so from the bottom. The return line was just a stub. The interior of the tank, was coated with WEST with a white color additive finish coat. All the inside corners were finished off with a cove of WEST. On the side of the tank, I contrived to make a "sight" tube, which allowed me to see how much diesel I had left. This was just a clear plastic hose with a little red bit of plastic that floated inside the hose. The side of the tank I had marked with black lines to indicate how much was in there.
The tank was made so that it had a "sump"...as it had to fit between two metal keel frames. Also the top of the tank was made with a cover, which I could remove to inspect the inside if I wanted too, though I never did open it, until after 10 years when I pulled the tank.
That WEST SYSTEM is remarkable stuff. Not sure if a diesel tank was ever considered in the design spec, but worked like a charm.
After 10 years, when I pulled the tank, I also opened it up. Besides a black residue on the bottom, the tank was spotless. It performed perfectly, the entire time.
I don't recall how big it was, maybe 20 US gallons or thereabouts. My engine at the time sipped fuel at about 1/3 gal/hour.
The replacement tank was aluminum, which a shop made for me. My original engine was replaced with a newer one, which also dictated a new tank.

[Stewie12]

I agree that it is probably a weld. Rewelding is probably the cheapest way out and it is unlikely that it will happen again.

[sva3]

Moeller makes a fuel sender with a diesel return built in to it.

[basenay]

Around 8 years ago had a leak in my aluminum diesel tank. My investigation showed a wooden plug tied to a nearby thru-hull had been bounced to rest against the tank sometime in prior 18 years. Research taught me that all wood leaches acetic acid (Google it. Fascinating reading about types of wood, curing & aging done by Canadian researchers) which slowly ate pinholes thru the aluminum where touching. Before deciding on repair vs replacement cut large access port to evaluate the rest of the tank which was pristine. Scab welded on for $175 US with a one year guarantee. Access port created and no further problems.

[Cheechako]

First, 70 litres is actually quite small even for local cruising. What is that... about 20 gallons?

If it can be removed readily you could fix it, the leak is almost always on the bottom at the edge weld or just a hole where it sits on supports. In one boat I had a hole corroded through a SS tank in 6-7 years from new (in the bilge)

But at 20 gallons, just buy a plastic tank that is made for permanent installation, not a Moeller. (Unless they make those too) Even West Marine used to sell those tanks although they had to be ordered.

[Boatyarddog]

Originally Posted by and4ew

My planned five-day coastal cruise was cut short when I found that diesel was leaking into my bilge. I checked the hoses and fittings and didn't find any diesel drips, and also the bilge slowly fills even when the engine is not running, so I surmised that the tank itself is leaking.

The tank sits in the bilge, a little off the bottom. It's mounted with fibreglass shims. It's not the original tank but was "custom made" and is stainless steel. It's 70 litres.

I'm guessing that the bottom, sitting so close to the bilge, has corroded. I haven't pulled it out yet as it's more than I could do by myself.

My options are to pull it out, find the leak, and weld. Alternatively, I could just replace it with something like a Moeller Marine fuel tank which are not metal. So my first question is: should I fix or replace?


Second question: the Moellers (and others) I've seen don't seem to have a return for diesel. Would I just add another spigot for that? If so, should it have a hose that goes down into the tank (like the feed-side does)?


Third question: my current tank is 70 litres. That seems like a lot for coastal cruising. I consume 1 litre per hour @ 5 kt and don't have to charge my batteries often. I feel like 30-40 litres would be fine for coastal cruising. Thoughts on this?

Your in Nova Scotia.
Can you get the tank out?

Make your own drawing and you add the fill, vent and uptake / return where you want it.
https://www.tankandbarrel.com/fuel-t...33f8074217b12c
Remember if you need one fuel bladders work well in unforgiving areas.

Just ordered a custom aluminum tank about 19 gal for our Cal 29
$475 includes shipping cost, about a 12 week wait.

Had to cut a hole in the engine bay to reef it out.
But it can be repaired.
SV Cloud Duster