Fuel tanks siphoning mystery

[Russell Clifton]

I need some input here. I have had this problem with fuel siphoning from the tanks on one side of the boat to the other side.I have a fuel manifold with shutoff valves on all the lines except the fuel return lines for the main engines and the two generators.

This week the fuel from the starboard forward tank moved back to the port aft tank. The only valve open at the manifold was the port aft tank ( to supply fuel for the heater),and the engine return lines. Both the "fuel out" and "return to" lines for that starboard tank were closed at the manifold, so I would think no fuel should have been able to get out of that tank and into the manifold.

I'm thinking maybe I should put shutoff valves on those engine and generator return lines?

 

[bayview]

I didnt understand your lines description but if there is any connection between the tanks fuel will balance out regardless of what those lines are called.

 

[timb]

mine has a line directly from tanks to tank .are you sure you don't have one? it goes to the bottom of the tank not the top like most lines.

 

[Russell Clifton]

I will take a closer look for a third line coming out of the tanks. Thanks

 

[rochepoint]

mine has a line directly from tanks to tank .are you sure you don't have one? it goes to the bottom of the tank not the top like most lines.

Same on our boat......

 

[sunchaser]

DeFever's tank setup, by design, usually has a crossover at tank bottom. Mine is valved and always closed. Also my 3 return lines have check valves located at the manifold. I can send you pictures if you PM your email. I am currently on vessel.

 

[Chrisjs]

If you have any possible open connection between the tanks (especially a cross over line for balancing) then fuel will flow "down hill" to the lower tank level. If your vessel has a list to one side, that can be enough to cause fuel flow. In that situation, fuel will keep flowing because the added weight of migrated fuel will cause an ever increasing list, encouraging greater and greater fuel movement. Best to keep the crossover closed except when intentionally moving fuel.