[JSK]

I've got a question regarding the fuel tank crossover valve on a 1990 3100 Open. When both tanks are full what is your experience in how the tanks drain? Will both tanks drain simultaneously or will one tank drain faster than another? Engines are twin Merc 8.2L.
Thanks John

[Uhehner]

When the crossover valve is open, the fuel line between them will act like a siphon and fuel will flow from the highest level to the lowest level tank. Both fuel gauges should read the same. With the crossover closed, the engine burning the most fuel will have the lowest tank. I always leave the crossover open. Along these lines, I NEVER have the battery switches in "both" except in an emergency. When in "both" if you have one bad battery, you will now have two dead batteries. Capt. George

[JSK]

George,
I assumed that was probably the case so it's good to hear you confirm that. I will find out the next time I fill up. Thanks, John

[JSK]

I happen to read in the owners manual the factory suggests the crossover be closed while running both engines, one off each tank.

[trit21]

I would think you should always leave the crossover closed as well. In case you have problems with one tank, you have them isolated and can run off one tank vs the 2. If the valve is open and you have a contamination in one tank, now all fuel is contaminated.

[Chris Burkard]

I think contamination is not a big deal. If you filled both tanks at the same station with the same hose, if one is contaminated, both are going to be. If you have a generator, it likely pulls from the Starboard tank. I think leaving the cross over open is not a big deal. If you really want to see how much each engine is drawing, then close it and keep track of how much fuel you put in each tank and if there is a difference, a trend will appear.

Good Luck!