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Old 03-18-2013, 04:33 PM   #21
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I want to add that up until two years ago when I completely overhauled Skinny Dippin's fuel system, she drew fuel from both and returned to only one. I never noticed anything out of the ordinary from the standpoint of unequal fill. That's weird.

I looked at my engine manual and could find a reference to ratio of burn-to-return, but I will look again. I got sidetracked by some other stuff I needed to look up. DOH!
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Old 03-18-2013, 04:48 PM   #22
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Here is an old reference discussion on this topic:
Fuel Return Ratio - SailNet Community

Seems like the return ratio can vary quite a bit from 1:1 (fuel burned to fuel returned) to 4:1 or 5:1 depending on the engine HP, configuration, manufacturer, etc.
Also relevant to fuel filtration since all that returned fuel is flowing through your filters and back to your tank. One way to help keep fuel clean via your Racors.
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Old 03-18-2013, 04:57 PM   #23
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I have heard that Lehmans return only a fraction what they consume...but have not been able to verify (pretty easy to check though).

I was hoping it was more for filtration purposes.
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Old 03-18-2013, 05:02 PM   #24
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in my case the return goes back into the filter but if the return is too large, you cooled the diesel- backline with an intercooler.
This is on bigboats normal.
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Old 03-18-2013, 05:46 PM   #25
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With 4 tanks, I'm thinking I'll run one engine on it's fwd tank, and the other on it's aft tank. For example, port engine on fwd port tank and stb engine on stb aft tank. Or vice-versa.

When I fuel up, I'll switch to the opposite tanks and run from those until the next fill.

My theory is that I'll always have two tanks that weren't filled at the same time and place, just in case.

Returns will always go to the same tank I'm drawing from.

I haven't had a chance to put any of this into practice yet. Another 6"-18" of snow is predicted for tomorrow
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Old 03-18-2013, 05:49 PM   #26
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Do you keep another tank ready for the lobsters??
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Old 03-18-2013, 06:00 PM   #27
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Do you keep another tank ready for the lobsters??
Hmmmm... I could convert the centerline 213 gallon potable water tank to a lobster holding tank pretty easily. Now, what would I find to drink?...
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Old 03-18-2013, 06:03 PM   #28
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Quote:
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I have heard that Lehmans return only a fraction what they consume...but have not been able to verify (pretty easy to check though).
I have heard the same thing.
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Old 03-24-2013, 05:03 PM   #29
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Hey everyone. I just climbed out of the engine room (36 Heritage Sundeck, single 5.9 cummins, with tanks port and starboard. I see where the fuel goes into the tanks, I see where the fuel goes from the top of the tank to the RACOR, and I see another line that I assume is the return (goes from engine block up to the top, next to the line that feeds the RACOR. What I DON'T see is how I can shut off the cross-over flow of fuel from the port to starboard. Again, I put 50 gals in port and it moved to starboard tank. I don't see a shut off value BETWEEN the tanks - I see a shut off at the bottom of each tank that the visual tubes are connected to, and I see a shut off from the fuel lines to the RACOR. What am I missing?
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Old 03-24-2013, 05:48 PM   #30
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.............. I see where the fuel goes from the top of the tank to the RACOR, ......
Doesn't the fuel come from both tanks into the filter? At some point, the lines from each tank join and feed the filter. That would be your crossover. You don't necessarily have a separate crossover tube or line. There should be a valve to valve off each tank. Somewhere, there should be a valve or valves that direct the return flow to either or both tanks.

BTW: Fuel is not coming from the top of the tank, there is a dip tube that goes to the bottom. Otherwise you would draw air, not fuel.
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Old 03-24-2013, 05:54 PM   #31
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Thanks Ron. Newbie on these dual tanks...There are valves at the bottom of each tank that feed the one "T" that feeds the RACOR. I found two values at the top of each tank. So, If I trace the line that goes to the other tank, that would be the crossover line. Just close, say the port crossover, and that should solve the problem?
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Old 03-24-2013, 06:26 PM   #32
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Thanks Ron. Newbie on these dual tanks...There are valves at the bottom of each tank that feed the one "T" that feeds the RACOR. I found two values at the top of each tank. So, If I trace the line that goes to the other tank, that would be the crossover line. Just close, say the port crossover, and that should solve the problem?
I believe the "T" is the crossover. If both valves are open (normal operation), fuel will flow from both tanks to the filter and from one tank to the other if the engine is off and the level in one tank is lower than the other.
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