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Old 08-03-2018, 10:50 PM   #1
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fuel valves and fuel tanks

I have a 1982 trawler with twin 120 lehmans. Im new to the boat. All my fuel valves are in open flow position including splash return valves. when I dip tanks its always port tank that consumes fuel. I can motor say 12 hours and starboard tanks may be down an inch, port tank down 5 inches, this is from both tanks full and measured. Were these tanks not designed with a crossover valve. Is this common. Thanks for opinions.
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Old 08-04-2018, 12:04 AM   #2
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We can’t see what you can, so you need to determine if you do have a crossover line, and if it is open and large enough to be functional.
Return fuel usually finds a “favorite”route, that of least resistance, so when both return valves are open, it still only feeds to the favored tank.
What are splash valves? Does the boat have a spill containment system at the filler? If so, I’d say that’s a really good thing to have!
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Old 08-04-2018, 06:44 AM   #3
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You didn't mention the manufacturer of your boat but I suspect most did install small dia crossover lines with a valve. It may take a number of hours for the tanks to balance. I would make a diagram of the feed and return lines. Sounds like both engines are returning to the starboard tank. Or the port return line is pinched.
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Old 08-04-2018, 06:04 PM   #4
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Fuel valves and tanks

Ty for your replies. Itís a Ocean Alexander 40 ft. All fuel lines look to be in great condition and all valves open. I do believe that yes perhaps fuel return splash is returning to starboard tank. Why I have no idea.
Appreciate the suggestions. Iíve had twin diesels before and have always had tanks burn evenly and remain balanced. Iíll get some better mind than mine to have a look
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Old 03-25-2023, 05:59 PM   #5
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I also have an Ocean Alexander 40 and had the same problem. My boat had both port and starboard fuel tanks feed into a stainless cylinder and out to each engine. There were shutoff valves going into and out from the cylinder. I removed the cylinder and put in a cross feed valve arrangement. I found that there were no check-valves or something in the cylinder that separated the two systems so basically fuel had to come from the tank with the least resistance. A 1/4 inch two way valve was put in the port 1/2 inch inlet hose for a little prime pump that cause a restriction, hence the engines burned mostly from the starboard tank. The same arrangement applied to the return fuel lines, which I also corrected with a cross feed valve.
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Old 03-25-2023, 06:08 PM   #6
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Try adjusting the valves so the starboard tank feeds the starboard engine only and returns to only the starboard tank. Set the port tanks to feed only the port engine and return only to the port tank.

I don’t mind both engines pulling and returning from one tank or separate tanks. I don’t like engines pulling and returning to multiple tanks simultaneously.
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Old 03-25-2023, 07:17 PM   #7
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Quote:
Originally Posted by geoshep View Post
I have a 1982 trawler with twin 120 lehmans. Im new to the boat. All my fuel valves are in open flow position including splash return valves. when I dip tanks its always port tank that consumes fuel. I can motor say 12 hours and starboard tanks may be down an inch, port tank down 5 inches, this is from both tanks full and measured. Were these tanks not designed with a crossover valve. Is this common. Thanks for opinions.
Do you perhaps have something else taking fuel from the port tank? Diesel hydronic heat would not use much fuel, but a large genset would be noticeable.

Second thought if you leave your crossover valve open, does the fuel in each tank eventually balance out or not. This may lead you towards the culprit.
~A
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Old 03-26-2023, 05:31 AM   #8
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Originally Posted by kapnd View Post
We canít see what you can, so you need to determine if you do have a crossover line, and if it is open and large enough to be functional.
Return fuel usually finds a ďfavoriteĒroute, that of least resistance, so when both return valves are open, it still only feeds to the favored tank.
What are splash valves? Does the boat have a spill containment system at the filler? If so, Iíd say thatís a really good thing to have!
Lehman 120s return maybe two ounces per hour, if that. It is not a factor in fuel tank imbalance on any boat equipped with Lehman 120s. Look elsewhere.
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