Fuel tank not balancing
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The single return line is very interesting. The reason for keeping the crossover line closed is so that the tanks don't become unbalanced causing a list which then causes the tanks to become even more unbalanced.
It's rare but years ago we had a sunken boat at our marina after an extremely low tide where it laid over on it's side and all the fuel transferred to the port tank. When the tide came back in it flooded the boat and it never refloated because of the angle and the water flooded the side of the bilge and didn't even activate the float until it was too late.
Boat was a 40' ish aft cabin.
It's rare but years ago we had a sunken boat at our marina after an extremely low tide where it laid over on it's side and all the fuel transferred to the port tank. When the tide came back in it flooded the boat and it never refloated because of the angle and the water flooded the side of the bilge and didn't even activate the float until it was too late.
Boat was a 40' ish aft cabin.
Brooksie
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Seeker has a list from having a generator removed and never re-trimmed. So if the crossover is opened, she lists more and more as fuel migrates to the low side tank from the highside tank. Never enough to cause a problem but noticeable.
Nomad Willy
Guru
My tanks rarely “balance” as I switch to one tank and switch to the other when I notice a bit of list.
Since I re-configured my fuel valve Positions I now can reach all four while underway. So I can raise one engine compartment hatch cover (floor) and change to draw from the other tank in about two minutes.
I one can’t notice the list it dos’nt need to be messed with .. IMO.
Since I re-configured my fuel valve Positions I now can reach all four while underway. So I can raise one engine compartment hatch cover (floor) and change to draw from the other tank in about two minutes.
I one can’t notice the list it dos’nt need to be messed with .. IMO.
Phyrcooler
Senior Member
As a 390 owner, it was my understanding that the crossover was supposed to be left OPEN. In the 5 years I had mine - i never closed it. Do NOT close the valve if you have a single returning to one side! The crossover is there to equalize the returning fuel.
Yes - some 390’s had a SLIGHT list to port... usually if owners replaced starboard side furniture with something lightweight. I had a HEAVY sleeper sofa in mine, and my boat remained balanced. I never had a problem with fuel system or balance. I never tried to dip my fuel tanks. Dipping really only works as a comparator if both tanks and filler piping are identical. I am not sure if that is the case - but you could look and see. Other than that - if you can get a dipstick in - you could determine relative, but not precise quantity.
Open the fuel fillers one at a time and see if you have air going into the fuller tank (as it transfers to less filled side. Because the transfer line is small - it will not be a huge rush of air. Use a piece of paper or card stock to see if it gets sucked against the opening. If fuel moves when one or the other fuel filler cap is opened - you probably have a vent issue. You can test both sides to determine which vent is clogged.
If you still have high fuel on one side and open caps make no difference - close off both fuel transfer valves - remove hose and check for obstructions. Open each valve with a bucket under to check for flow.
Lastly if fuel is ok and you have the slight port side list - consider your water tank locations and fill status as others have mentioned. We only regularly used our primary tank which was located centerline behind the stairs going below. We had two aft tanks that could effect trim as you could pull from them one at a time. Not all 390’s had the same water tankage setup.
Best regards
Yes - some 390’s had a SLIGHT list to port... usually if owners replaced starboard side furniture with something lightweight. I had a HEAVY sleeper sofa in mine, and my boat remained balanced. I never had a problem with fuel system or balance. I never tried to dip my fuel tanks. Dipping really only works as a comparator if both tanks and filler piping are identical. I am not sure if that is the case - but you could look and see. Other than that - if you can get a dipstick in - you could determine relative, but not precise quantity.
Open the fuel fillers one at a time and see if you have air going into the fuller tank (as it transfers to less filled side. Because the transfer line is small - it will not be a huge rush of air. Use a piece of paper or card stock to see if it gets sucked against the opening. If fuel moves when one or the other fuel filler cap is opened - you probably have a vent issue. You can test both sides to determine which vent is clogged.
If you still have high fuel on one side and open caps make no difference - close off both fuel transfer valves - remove hose and check for obstructions. Open each valve with a bucket under to check for flow.
Lastly if fuel is ok and you have the slight port side list - consider your water tank locations and fill status as others have mentioned. We only regularly used our primary tank which was located centerline behind the stairs going below. We had two aft tanks that could effect trim as you could pull from them one at a time. Not all 390’s had the same water tankage setup.
Best regards
rgano
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From the description, the boat is equipped with top-feed (standpipe) fuel supply. This introduces another set of issues. What if the side with the most fuel has developed a pinhole in the standpipe or even farther along toward the Racor - not so much that engine performance suffers but maybe enough for a "fuel preference" to get established?
My single 6LPA Yanmar boat came from the factory with the fuel supply to the engine teed to a single Racor from the bottom-fed sluice (crossover) line and the return only to port AND the fuel gauge on the console reading only port. How dumb is all that mess?
If I had the OP's boat, I would decommission the standpipe feed and go to the system I now have with the bottom feed via the sluice line feeding to twin selectable Racors, selectable return to either tank, and a selector switch to read the level of either tank at the console. NOW you have complete control of the tank levels.
Do check the vents!
My single 6LPA Yanmar boat came from the factory with the fuel supply to the engine teed to a single Racor from the bottom-fed sluice (crossover) line and the return only to port AND the fuel gauge on the console reading only port. How dumb is all that mess?
If I had the OP's boat, I would decommission the standpipe feed and go to the system I now have with the bottom feed via the sluice line feeding to twin selectable Racors, selectable return to either tank, and a selector switch to read the level of either tank at the console. NOW you have complete control of the tank levels.
Do check the vents!
If I do end up with a diesel trawler, it will be my first diesel powered boat with more than one fuel tank (previous were sailboats), so my first experience running with various valves and etc.
Reading through this thread I was able to gain a better understanding of how the system(s) work. OP: Sorry you have a problem, but your thread has been enlightening so thank you.
I now have a question that might also be of interest to the OP.
So let's say that like the OP, you have a single engine, two (saddle) tanks, a crossover, and only ONE return line (to only one side's tank). Presuming one does not mind doing the labor, is there any good reason not to add a return (with appropriate valves) to the other tank? Or to put it another way, what is the advantage to the user of the OP's "return to one side only so must leave crossover valve open" installation? Obviously fewer valves and fuel lines for the builder to install, but for the operator? Was it done as a "keep it simple and let's not confuse people with choices" type thing?
In summary, I want to test out my thought which is that while a system with return valves to both tanks requires more thought and action while operating; it also gives one more ability to control for list (which can be exacerbated by a waterfall effect as the low side tank encourages more and more fuel to head over that way through the "must be open" crossover). OTOH, the "only one return and must keep crossover open" is the "you don't need to think about it" approach (AS LONG AS the boat does not start to create a cascade of listing).
Thanks for any replies and OP, I hope this is useful to you as well (why I did not start another thread at least as of yet).
Frosty
Reading through this thread I was able to gain a better understanding of how the system(s) work. OP: Sorry you have a problem, but your thread has been enlightening so thank you.
I now have a question that might also be of interest to the OP.
So let's say that like the OP, you have a single engine, two (saddle) tanks, a crossover, and only ONE return line (to only one side's tank). Presuming one does not mind doing the labor, is there any good reason not to add a return (with appropriate valves) to the other tank? Or to put it another way, what is the advantage to the user of the OP's "return to one side only so must leave crossover valve open" installation? Obviously fewer valves and fuel lines for the builder to install, but for the operator? Was it done as a "keep it simple and let's not confuse people with choices" type thing?
In summary, I want to test out my thought which is that while a system with return valves to both tanks requires more thought and action while operating; it also gives one more ability to control for list (which can be exacerbated by a waterfall effect as the low side tank encourages more and more fuel to head over that way through the "must be open" crossover). OTOH, the "only one return and must keep crossover open" is the "you don't need to think about it" approach (AS LONG AS the boat does not start to create a cascade of listing).
Thanks for any replies and OP, I hope this is useful to you as well (why I did not start another thread at least as of yet).
Frosty
rgano
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Frosty, you seem to have it correctly thought out. Yes, it is dead simple to add a return to a second tank assuming like my boat, the tank connection was already there, just plugged. MS obviously made these simple and inflexible systems for the masses who just want to run the boat hoping everything works OK all the time. I prefer to have a hand in where fuel comes from and goes to.
Thank you, Rich.
I knew this was something I was going to need to "get my head around" at some point, and the OP (and up-thread responses) provided just the head start I needed. I think I'd prefer the method where you need to think about it a little bit, but have more control. I'm sure I'd need to print out reminders for myself at first (such as always have a new destination for the return before shutting off the other one while engine running; this is a familiar concept from something like alternator output, but I didn't know it also applied to fuel pump).
Frosty.
I knew this was something I was going to need to "get my head around" at some point, and the OP (and up-thread responses) provided just the head start I needed. I think I'd prefer the method where you need to think about it a little bit, but have more control. I'm sure I'd need to print out reminders for myself at first (such as always have a new destination for the return before shutting off the other one while engine running; this is a familiar concept from something like alternator output, but I didn't know it also applied to fuel pump).
Frosty.
Knot Thirsty
Member
fuel tank balancing
I had the same issue with twin tanks, twin engines, and genny drawing from one tabk only. It seemed to start after I had a pre engine "fuel cleaning centre" installled and after the tanks were filled. As it turns out, and after all logical reasons were dismissed, the engines draw fuel by taking the path of least resistance. As the one tank drops the pressure from the fuller one should make it easier to draw from. I didn't appreciate the list and the potential for it to not start drawing from the fuller tank so I installed a shut off valve where there normally would be a free from through the crossover. So now all the fuel from the port tank goes through the.port fuel filter first and the starboard tank feeds both the stbd fuel filter and genny first. If the stbd empties sooner I can open the cross over valve. Good luck. Stay safe.
Paul
I had the same issue with twin tanks, twin engines, and genny drawing from one tabk only. It seemed to start after I had a pre engine "fuel cleaning centre" installled and after the tanks were filled. As it turns out, and after all logical reasons were dismissed, the engines draw fuel by taking the path of least resistance. As the one tank drops the pressure from the fuller one should make it easier to draw from. I didn't appreciate the list and the potential for it to not start drawing from the fuller tank so I installed a shut off valve where there normally would be a free from through the crossover. So now all the fuel from the port tank goes through the.port fuel filter first and the starboard tank feeds both the stbd fuel filter and genny first. If the stbd empties sooner I can open the cross over valve. Good luck. Stay safe.
Paul
bill.kimbell
Veteran Member
jhall767 Why? "...that crossover valve is required to be closed when underway."
NCheaven
Senior Member
Had that issue, but not as pronounced. Closed return to more full tank, starboard, hoping all return to less full tank, port, would insure good flow, no clogs. Helped a little. Four batteries and helmsman all on starboard is probably the rest of the problem.
