Fuel leak

[Dovnar]

Hello,

We have a 55 foot catamaran Swiss Cat

Over the past few days we are having fuel overflowing from the starboard tank.. Seems to have happened after overfilling it a few days ago.
Seems as if the starboard tank is sucking out the fuel from the port tank. The breather is also full of fuel.

We tried to only use the starboard engine to consume the fuel with it keeps on overflowing. The fuel transfer pump is also set to off


Anyone else had a similar issue?

Thanks !

Michel

[noelex 77]

Welcome to the forum Michel.

Have you any fuel transfer of polishing pumps?

[Tin Tin]

Couple of things.
Are your fuel tanks interconnected? If so is there a shutoff valve, it could be the fuller tank is siphoning back to the other tank. DO you have a transfer pump, that could be leaking too.



If the breathers are full then it is way overfull, you need to go for a drive or suck some out into a fuel can. If there has been a large temperature day time increase then the fuel may have expanded and caused the breathers to overflow plus put pressure on the tank filler pipe fittings which may be loose, they should be double clamped.


The seal around the gauge sender unit if you have one may be in need of replacement. Any other holes into the tank may also need re-sealing, top and bottom if it has a drain plug.

[Uncle Bob]

To which tank is the fuel return line currently connected??

[Dovnar]

Originally Posted by Tin Tin

Couple of things.
Are your fuel tanks interconnected? If so is there a shutoff valve, it could be the fuller tank is siphoning back to the other tank. DO you have a transfer pump, that could be leaking too.



If the breathers are full then it is way overfull, you need to go for a drive or suck some out into a fuel can. If there has been a large temperature day time increase then the fuel may have expanded and caused the breathers to overflow plus put pressure on the tank filler pipe fittings which may be loose, they should be double clamped.


The seal around the gauge sender unit if you have one may be in need of replacement. Any other holes into the tank may also need re-sealing, top and bottom if it has a drain plug.

Thanks Tintin
the 2 fuel tanks are interconnected , i shut off the valves between the two systems and it was still overflowing my stb tank through siphoning of the left tank
I think the shut off valves are defective and or the generator lines were acting as a bypass for siphoning. I turned off the genset lines
Yesterday I had overflow through the stb tank breather ( big mess)
I am going today to run the STB engine with the 2 tanks disconnected and with the tank filler open so there is no siphoning possible
Any idea on your side ?
will keep you posted
Vincent on Aurora 2 ( using Michael forum discussion page )

[Dovnar]

Originally Posted by Tin Tin

Couple of things.
Are your fuel tanks interconnected? If so is there a shutoff valve, it could be the fuller tank is siphoning back to the other tank. DO you have a transfer pump, that could be leaking too.



If the breathers are full then it is way overfull, you need to go for a drive or suck some out into a fuel can. If there has been a large temperature day time increase then the fuel may have expanded and caused the breathers to overflow plus put pressure on the tank filler pipe fittings which may be loose, they should be double clamped.


The seal around the gauge sender unit if you have one may be in need of replacement. Any other holes into the tank may also need re-sealing, top and bottom if it has a drain plug.

Hello

Tin Tin,

So after trying to empty out the tanks, it seemed to have worked but it all started again after starting the generator. So we now know that the problem is coming from having the generator on….
Would you have any ideas why?

Thanks again!

[Uncle Bob]

I will ask again, which tank is the fuel return line connected and returning to? Is it the same tank from which fuel is being drawn?

[Dovnar]

Originally Posted by Uncle Bob

I will ask again, which tank is the fuel return line connected and returning to? Is it the same tank from which fuel is being drawn?

Hi uncle Bob,

Sorry for the late reply. We’ve been knee deep in fuel… literally .
Each tank has its own return line as per the captain

[Uncle Bob]

Originally Posted by Dovnar

Hi uncle Bob,

Sorry for the late reply. We’ve been knee deep in fuel… literally .
Each tank has its own return line as per the captain

Then the fuel system must have some cross tank connection, valving, transfer pump/polishing pump that enables fuel to be drawn from one tank and returned to the other. You say that an interconnecting valve has been closed but there must be some other connection that perhaps you are unaware of.

[Dovnar]

Thanks
Yes I have shut off the interconnection between the 2 tanks ( used for transfer )
I have open up all the tank fillers ( both the tank filler breather and tank filler hose ) to prevent siphoning
I thought everything was ok now for two days until I run the genset for 4 hours today
Tonight again I had I overflow of the stb tank
I think the right tank gets filled by the port tank through the generator line

I have switched all geneset lines to draw and return to the port side tank
Let’s keep our fingers crossed
Any ideas ?
Vincent

[Uncle Bob]

Originally Posted by Dovnar

Thanks
Yes I have shut off the interconnection between the 2 tanks ( used for transfer )
I have open up all the tank fillers ( both the tank filler breather and tank filler hose ) to prevent siphoning
I thought everything was ok now for two days until I run the genset for 4 hours today
Tonight again I had I overflow of the stb tank
I think the right tank gets filled by the port tank through the generator line

I have switched all geneset lines to draw and return to the port side tank
Let’s keep our fingers crossed
Any ideas ?
Vincent

Any fuel system that has more than one tank must have the return line routed to the same tank that it is drawing from. If changing tanks then manifolds on the supply and return sides make this an easy task.

[Tin Tin]

On our boat the generator tank selection valve was a 6 port fuel valve (Groco I think) that had 6 lines going in to it, 2 from each tank and 2 to the generator so it was not possible to get them mixed up. https://www.groco.net/products/valve...-6-port-series