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Old 10-17-2016, 09:31 PM   #1
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Fuel tanks question

On our last boat we had two fuel tanks as we now have on our 2003 30'
Mainship pilot II. The old rig had valves for each tank that would allow you to draw from either tank.Each tank had it's own sending unit. On the console was a two position switch and one fuel gauge. The switch was used to check the level in the port or starboard tank. On the Mainship we have one fuel gauge and no selector switch. So I am assuming fuel is drawn from both tanks simultaneously. If so does only one tank have a sending unit? Thanks

regards Holty
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Old 10-17-2016, 11:27 PM   #2
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Just thinking out loud...is it possible that the tanks have an open cross-over between them. If so, the level in the tanks would always equalize and the need for two sending units would be unnecessary.
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Old 10-18-2016, 05:45 AM   #3
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Just thinking out loud...is it possible that the tanks have an open cross-over between them. If so, the level in the tanks would always equalize and the need for two sending units would be unnecessary.

would always equalize
That's logical but boats aren't logical. I have 2 x 100liter tanks with a cross over the starboard tank always empty's down first by about 20 liters I know this because the starboard tank always takes more fuel to fill to the brim than the port tank
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Old 10-18-2016, 07:11 AM   #4
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It would depend on how the tanks are plumbed. If the crossover is from bottom of tank to bottom of tank then the tanks can equalize. If the tanks are connected by a hose that is at any point above the tank then they can't equalize. Also is the return line going to one or both tanks?

Return lines are notorious for finding 'the path of least resistance' and mostly flowing to one tank or the other. I usually run off one side and return to same side to prevent overflows. My Perkins burns in the vicinity of a gallon an hour. But pumps 8 an hour. There's a LOT of fuel moving you don't even see!
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Old 10-18-2016, 10:33 AM   #5
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Holty,
Yes, you only one sending unit. I think it's in the starboard side tank. Tanks do have 1/2 " hose that cross connects both tanks. Search mainship forum for sending unit. Someone has posted about installing a second sending unit in the port tank and adding a switch at the console so you can read both tank levels.
Jeff.
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Old 10-18-2016, 04:10 PM   #6
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Thanks jskinner.

regards Holty
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Old 10-18-2016, 05:23 PM   #7
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If I leave the cross feed valve open the fuel moves to the port tank and makes the boat lean to the port.

Fred P...........
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Old 10-18-2016, 06:02 PM   #8
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If I leave the cross feed valve open the fuel moves to the port tank and makes the boat lean to the port.

Fred P...........
You sure it's the cross feed valve you're opening?
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Old 10-18-2016, 06:31 PM   #9
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Yes it is the cross feed. I have a 8D battery on the port side and when the water tank on the starboard side gets a little low the fuel moves to the low side and the low side become lower and more fuel moves port.

Fred P................
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Old 10-18-2016, 07:04 PM   #10
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Yes it is the cross feed. I have a 8D battery on the port side and when the water tank on the starboard side gets a little low the fuel moves to the low side and the low side become lower and more fuel moves port.

Fred P................
Perhaps you should add a crossover between your water tanks.
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Old 10-18-2016, 09:14 PM   #11
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We just have one water tank. If for any reason one side of the boat is low with the fuel cross flow open the fuel will flow to the tank on the low side of the boat which will make that side of the boat even lower and more fuel will move to low side of the boat and so on.

Fred P......................
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