Full tank...... empty tank?

[kgh]

My boat has a twin tank set up with diesel returns and feeds going to the top aft corner of each tank. I have a set of shut off valves that allow to run port or starboard or combinations, usual set up. Heres the thing, all last year the port tank level went down and the starboard stayed high. I though must be a faulty sender but when I removed the sender I found the tank was brim full!! I never more than half filled it so I'm assuming the port tank has fed into starboard, how is this possible as both tanks are set to feed engines equally? Any ideas?

KGH

 

[Bandit]

Check if your diesel return lines feed back to the wrong tank?

Assuming your feed lines go from port to port and starb to starb then check your return lines does port go back to Port etc?

A balancing line between port and starb tanks does not generally have a one way valve.

Check your shut off valves on the crossover system are set correctly and its not only drawing from the starb tank ?