Fuel tank leak

[MapisM]

Not easy is actually an understatement, also because you should:
1) seal perfectly all openings (refill, overflow, pickup, return, level sensor), for obvious reasons;
2) pressurize the tank with air at the pressure it's rated for (usually, 0.20 to 0.25 bar), but NO MORE, to avoid much worse damages;
3) fill the tank before going ahead with (2), because measuring a pressure decrease in a large tank filled only with air, at such relatively low pressure, would take forever, due to compressibility of air.

 

[Mistroma]

Not easy is actually an understatement, also because you should:
1) seal perfectly all openings (refill, overflow, pickup, return, level sensor), for obvious reasons;
2) pressurize the tank with air at the pressure it's rated for (usually, 0.20 to 0.25 bar), but NO MORE, to avoid much worse damages;
3) fill the tank before going ahead with (2), because measuring a pressure decrease in a large tank filled only with air, at such relatively low pressure, would take forever, due to compressibility of air.

Pretty much the conclusion came to. A lot of effort but no guarantee of proving much unless it was done properly. I did say that the one positive was that Bouba could now speed things up a bit. The tank has now been isolated a few months late but better late than never. I wouldn't pressure test with the kit available but extra fuel can be added and the tank pressurised to speed up any leak. Even a pinhole should leak significantly with the tank kept under pressure for several hours.

It should be obvious pretty quickly and "watery liquid" doesn't count. The fuel would end up on top of any water that's found its way under the tank and be in sufficient quantity to not look like water.

I wouldn't mess around at this stage, add at least 20 litres and then pressurise. Pumping air in won't help much when level might just be close to a leak. It really has to be above that point and should squirt out under pressure.

 

[vas]

Was a proper pressure test actually made? And if yes, how?

Sorry for asking, rather than go back through 500 posts...

no it wasn't, a vice-grip with two pieces of wood clamping on a fuel hose is not (even remotely) a serious way of blocking a tank outlet/inlet.
Bouba, what's going to happen on Wednesday then? bit confused tbh!

 

[Portofino]

Where’s the pics of the flappy Passerelle fix ……the internal reinforcements , the mounting of the thing ?

Lets tie off one disaster before embarking on another ps .

 

[Bran]

Post 74, picture shows test pressure, 0.35 bars for max 30 minutes. Would not recommend exceeding this.

 

[Bouba]

no it wasn't, a vice-grip with two pieces of wood clamping on a fuel hose is not (even remotely) a serious way of blocking a tank outlet/inlet.
Bouba, what's going to happen on Wednesday then? bit confused tbh!

The pipe with the clamp with wood was folded and clamped with three clamps!
I topped up the tank with another ten litres this morning...on Wednesday I will pump out the bilge and see what happens...by my calculations the fuel level is now higher than the hole

 

[vas]

OK, since I'd give you 0.001% chance of NOT pumping fuel, what will you do next? Maybe it's time to think about it.
Mind, even if you don't pump fuel, I guess you'll add another 10lt and two days later you will be pumping fuel, what then?

 

[Bouba]

Where’s the pics of the flappy Passerelle fix ……the internal reinforcements , the mounting of the thing ?

Lets tie off one disaster before embarking on another ps .

My passerelle is reasonably stable...I did a survey of all boats (couldn’t find an Itama) and mine was more stable than every boat except Princess...so my plan was to add a little reinforcement and equal Prinny. I made my design...shaped the stainless steel and practiced my welding...I was all set to go when I smelled fuel....

 

[Bouba]

OK, since I'd give you 0.001% chance of NOT pumping fuel, what will you do next? Maybe it's time to think about it.
Mind, even if you don't pump fuel, I guess you'll add another 10lt and two days later you will be pumping fuel, what then?

I have resigned myself to the fact that my tank is holed...after Wednesday I will contact the mechanics and discuss the logistics...whether they will do it in my yard or I take the boat to them?
In the meantime I will hope and pray that the bilge is dry....

 

[MapisM]

The pipe with the clamp with wood was folded and clamped with three clamps!

Sorry J if you already mentioned this, but I couldn't find the post with a quick browse of previous pages.

What did you do exactly, and which results did you get?
There's MUCH more than sealing a hose or three, for properly testing an already installed fuel tank.
Assuming it's even possible, which is not always the case.

 

[Portofino]

My passerelle is reasonably stable...I did a survey of all boats (couldn’t find an Itama) and mine was more stable than every boat except Princess...so my plan was to add a little reinforcement and equal Prinny. I made my design...shaped the stainless steel and practiced my welding...I was all set to go when I smelled fuel....

Ok just to clear the Passerelle problem is not resolved?

 

[Bouba]

Sorry J if you already mentioned this, but I couldn't find the post with a quick browse of previous pages.

What did you do exactly, and which results did you get?
There's MUCH more than sealing a hose or three, for properly testing an already installed fuel tank.
Assuming it's even possible, which is not always the case.

I clamped and bunged every opening (six all together) and pumped air from a pump with a gauge that was calibrated for low pressure...about 3 psi (0.2 bar) for ten minutes. Used soapy water to check my clamps. The needle gauge did slowly drop but I was never confident that it was steady..but there was lots of pressure in the tank when I finally unclamped it. I then repeated it.
The result told me that if there is a hole it is small. And that the hole is about the quarter tank level

 

[Mr Googler]

Honesty boubs……engine out won’t be the drama you think it is. Few hours and it’ll be sitting on the dock. You could give it a nice service and touch up. Only a single engine so plenty of room.

 

[Poignard]

Honesty boubs……engine out won’t be the drama you think it is. Few hours and it’ll be sitting on the dock. You could give it a nice service and touch up. Only a single engine so plenty of room.

Also clean and paint the area under the engine.

 

[Bouba]

Honesty boubs……engine out won’t be the drama you think it is. Few hours and it’ll be sitting on the dock. You could give it a nice service and touch up. Only a single engine so plenty of room.

I need a long boom crane, a place to store it (I know you hired a workshop) and many helping hands...plus I don’t have the lower back for it anymore. The job will be handed over to a boatyard while I sit in a corner and gently weep?

 

[Bouba]

Can I just say...my engine is spotless and painted and my bilge (the bit you can reach) is also spotless
P.s. even my fuel tank is shiny

 

[MapisM]

I clamped and bunged every opening (six all together) and pumped air from a pump with a gauge that was calibrated for low pressure...about 3 psi (0.2 bar) for ten minutes.
Used soapy water to check my clamps. The needle gauge did slowly drop but I was never confident that it was steady..but there was lots of pressure in the tank when I finally unclamped it. I then repeated it.
The result told me that if there is a hole it is small. And that the hole is about the quarter tank level

Mmm... I must be missing something, because I can't for the life of me understand your conclusions.
I mean, the hole position, first and foremost, but also its size.
What was the fuel level during this test?

 

[Bouba]

Mmm... I must be missing something, because I can't for the life of me understand your conclusions.
I mean, the hole position, first and foremost, but also the hole size.
What was the fuel level during this test?

The leak had stopped before I pressure tested it (with about 200 liters left in the tank) and no more fuel came out in the pressure test so that confirmed the height of the hole.
And the test showed that the tank held pressure very well...so the hole could not be big

 

[Mistroma]

The leak had stopped before I pressure tested it (with about 200 liters left in the tank) and no more fuel came out in the pressure test so that confirmed the height of the hole.
And the test showed that the tank held pressure very well...so the hole could not be big

Reasonable conclusion as the leak had dried up ages ago as far as I remember. It didn't prove the tank had a leak but was the most likely reason. A leak elsewhere could have also have stopped due to lack of pressure difference or something just swelling up eventually.

I would still suggest that you pressurise the tank as you have the kit and everything is sealed apart from the filler. It will speed up any leak once extra fuel is in the tank.

Of course there's always the very faint chance something inside the tank floats over a pinhole and seals it. Really not very likely but I remember my old Hillman Imp stopping suddenly and being fine after waiting 10 minutes. It happened several times and I couldn't find any blockages until I removed the sender and peered inside.

There was a small piece of brown paper floating around in the petrol. The problem never returned once it was removed. I assume that it would float near the outlet once in a blue moon and be sucked ovder it.

 

[MapisM]

The leak had stopped before I pressure tested it (with about 200 liters left in the tank) and no more fuel came out in the pressure test so that confirmed the height of the hole.
And the test showed that the tank held pressure very well...so the hole could not be big

Ok, so you tested an 800 liters tank by filling 3/4 of it with air pressurized at 0.2 bar for ten minutes.
You previously said that during that timeframe you could see the gauge dropping slowly.
Just guessing a bit now, did it drop to what, 0.18 bar? If the drop would have been even less, you would have struggled to see it on the gauge, so maybe it was even more - but let's stick to 0.18, for sake of reasoning.

A bit of math (didn't do it myself - easier to use a Boyle's law online calculator! ) tells us that a pressure reduction from 0.2 to 0.18 bar with a total volume of 600 litres implies a leak of exactly 10 litres of air.
Now, let's leave aside the fact that I'd be worried by a leaking tank regardless of how "big" the hole is, if nothing else because there's only one way the hole can develop over time, and it's not in the direction of getting smaller.
Fact is, the only conclusion you can draw from your test is that there's a 1 liter/minute leak.
Or more, if the pressure actually dropped to less than 0.18 bar - and I have a funny feeling that it could well have been the case.
Personally, I'm not sure I'd dismiss that as "not big".

Mind, this is all theoretical of course, and even assuming that the leak is exactly at 1/4 of the total tank height, I guess that after filling up, you never found 600 liters of fuel (i.e. 3/4 of tank) in the bilge after 10 hours - which is what would happen with a constant leak of 1 liter/minute.
But that's because the real world leak rate depends also on other considerations: first and foremost, actual fuel pressure at 1/4 tank (even if it depends on how high the tank is) is certainly much lower than 0.2 bar. Besides, I guess it's a bit easier for air to find its way out compared to fuel.
Then again, whether it takes one minute or one day for one liter of fuel to leak out of the tank, it's something that needs attention anyway!

Sorry to sound a bit scaremongering, but I had to bang my head against the wall on this matter before, and I know how misleading these tests can be.
Good luck!