Fuel tank not balancing

[Cartouche]

We have a Mainship 390 with 2 Tanks port and starboard. I noticed a considerable list to Port yesterday (Fuel gauge was showing just off full) yesterday we fuelled up for the first time this year, and the starboard tank took $225.00 of diesel and the Port tank only took $50.00 of Diesel. both valves are open on the Equalization line at the bottom of the tanks and both Valves are open to the Racor, . I know the generator draws from the Starboard tank but we have only run it at Launch for about 5 minuets - any thought's

 

[DDW]

I have this problem too though to a lesser extent. There are ganged valves that will switch the source between tanks, they have two circuits because you must switch the fuel return at the same time or you will be pumping spill fuel from one tank to the other until it overflows. As long as the genset returns to the tank it is drawing from, it isn't an issue.

 

[DavidM]

Do you have twins or a single?

David

 

[Lollygag1]

Had same issue last year, turns out the port side fuel filter was clogged. Once i replaced it boat was fine.

 

[Cartouche]

Do you have twins or a single?

David

Single Yanmar 6LP

 

[Cartouche]

Had same issue last year, turns out the port side fuel filter was clogged. Once i replaced it boat was fine.

Only has one set of filters for both tanks going to a single engine

 

[jhall767]

If both balancing valves are open and the tanks aren't balancing out that is the place to start. The supply/return valves shouldn't affect this.

Can you confirm the fuel level in the each tank?

What size is your crossover line?

Double check that both valves are open 100% and it's not an issue with the handle or stem.

If your crossover line is actually blocked I would be concerned that something is in the tank/line and will likely block the fuel feed to the engine at some point.

However it is more likely that there is a valve not set properly or there's another valve in the crossover link that has been closed. Maybe by a helpful mechanic in the offseason?

Can you post pictures of the valves?

 

[Cartouche]

If both balancing valves are open and the tanks aren't balancing out that is the place to start. The supply/return valves shouldn't affect this.

Can you confirm the fuel level in the each tank?

What size is your crossover line?

Double check that both valves are open 100% and it's not an issue with the handle or stem.

If your crossover line is actually blocked I would be concerned that something is in the tank/line and will likely block the fuel feed to the engine at some point.

However it is more likely that there is a valve not set properly or there's another valve in the crossover link that has been closed. Maybe by a helpful mechanic in the offseason?

Can you post pictures of the valves?

Both are like this

 

[DavidM]

Possibly the fuel return is going to a different tank than the fuel supply is coming from. With P&S tanks feeding a single engine, the flow often favors one side. The balancing line is too small or maybe it is partially plugged to keep them even.

David

 

[tiltrider1]

What we are seeing is the shut off for the tank. There could very likely be a cross over valve some where else. I would follow the port fuel line all the way to the engine and then I would follow the return line all the way back to the tank. I suspect you will find more valves.

 

[Cartouche]

What we are seeing is the shut off for the tank. There could very likely be a cross over valve some where else. I would follow the port fuel line all the way to the engine and then I would follow the return line all the way back to the tank. I suspect you will find more valves.

No this is the cross over - the shut off for the tanks is at the other end at the top of the tank close to the Racor, when I am changing the Racor I do not touch the valve shown just the one at the top on each tank that goes directly to the Racor

 

[Cartouche]

What we are seeing is the shut off for the tank. There could very likely be a cross over valve some where else. I would follow the port fuel line all the way to the engine and then I would follow the return line all the way back to the tank. I suspect you will find more valves.

This line goes directly to the other tank with the same shut off at the other tank, Sorry the Picture for some reason is back to front

 

[Pmcsurf1]

How much is the boat listing? Maybe you need some ballast to even things out. If you list too much to one side the fuel will flow to that tank. Was your boat level at the time?

 

[tiltrider1]

Follow the fuel lines from the tanks to the engine and then the return back to the tank. There are more valves some where.

 

[Cartouche]

How much is the boat listing? Maybe you need some ballast to even things out. If you list too much to one side the fuel will flow to that tank. Was your boat level at the time?

You know I think you have nailed it the boat lists to port slightly when both tanks are full, (we took the couch out which was a lot heavier), and all the Galley cupboards are on the port side, and probably as I run the engine it is drawing from both tanks and as they go down the starboard tank empties into the port tank when the boat is at rest, and increases the list, (Thus the Transfer) I am going to shut off the starboard shut off and see what fuel I put in each tank next fill up. I

 

[Solly]

Might also look into the water tanks to see if they are affecting the list. Not sure how many or where they are. I know our 1985 34 trawler lists to starboard when the water tanks are empty. Batteries are on the starboard side.

 

[MurrayM]

Responded to your other thread. Have you checked to see if the vent line to the tank that is not emptying is plugged?

 

[Codger2]

(we took the couch out which was a lot heavier),

New information...different solution! Makes sense. Too many suggestions without knowing the whole story!

 

[jhall767]

You know I think you have nailed it the boat lists to port slightly when both tanks are full, (we took the couch out which was a lot heavier), and all the Galley cupboards are on the port side, and probably as I run the engine it is drawing from both tanks and as they go down the starboard tank empties into the port tank when the boat is at rest, and increases the list, (Thus the Transfer) I am going to shut off the starboard shut off and see what fuel I put in each tank next fill up. I

Not sure if you are doing this but that crossover line is required to be closed when underway.

Also I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.

BTW extra beer is always good portable ballast.

 

[mvweebles]

Similar problem on my Willard 36 with single Perkins 4.236 75hp and twin saddle tanks of 225 gals each, though to a lessor degree than OP. For me, boat needs to be re-trimmed - no clogs or otherwise. Over the years, she got a bit heavy on port side, which caused more fuel to flow to port side, and trim gets worse until she has 3-4 degree of trim at rest. Not much but annoying. When she's done with her refit, I'll put 150 gals in each tank then use movable lead ballast to trim her to zero degrees trim. I consider this normal after 50 years and a major refit.

Peter

 

[markpierce]

Have four tanks and single engine, two tanks on each beam, using one tank at a time. Easy to balance using valves (choice among four to-engine and same number for return while running the engine) and sometimes use an in-system pump, rarely necessary.

 

[DrissZougari]

Cartouche,
My MS390 used to list a little to Port after a long cruise of more than 5 hrs however, the tanks will auto balance via the crossover line once I stop for the night. I have the same setup with a single Cat3116 with two RACOR–75500FGX2 Turbine Series Fuel Filter/Water Separator. I was able to resolve my listing issue by using the port tank only once It was 1/2 full. this way, the fuel pump will remove any blockage from the supply hose from the port tank. in my case it, there was some what clogged as I had some dark green stuff in the filter.
swapped the filter and have not had the listing issue anymore for a over a year so far.

 

[Cartouche]

Not sure if you are doing this but that crossover line is required to be closed when underway.

Also I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.

BTW extra beer is always good portable ballast.

Many thanks so to be clear I should shut off the Crossover line, and then select which tank to draw from right now I have the crossover open and both tanks drawing to the Racor

 

[Cartouche]

Not sure if you are doing this but that crossover line is required to be closed when underway.

Also I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.

BTW extra beer is always good portable ballast.

Not sure why but the mainship Manual tells me to not close the crossover line when engine is running, any ideas as to why? (Page 5.4)

 

[C lectric]

A guess but if there is only one return line to one tank then all the return fuel will stay in that tank and cause a loss of fuel. The balance line may be needed to at least try to effect a balance.

When closing the balance line the return line should also be directed to the same tank you are drawing from or you could actually overfill the tank that the return fuel goes to and dump fuel out of the vent line. Don't ask how I know.

I looked for any mention of two return lines, one to each tank, with valves so the return fuel can be directed. If the fuel is not able to be directed to the tank being drawn form then you need the balance line.

Maybe a project for another day to correct.

If you go this route, directable return lines then you must ensure that you NEVER shut of the active one before opening the other valve or injector pump damage can occur.

 

[Al]

Similar problem on my Willard 36 with single Perkins 4.236 75hp and twin saddle tanks of 225 gals each, though to a lessor degree than OP. For me, boat needs to be re-trimmed - no clogs or otherwise. Over the years, she got a bit heavy on port side, which caused more fuel to flow to port side, and trim gets worse until she has 3-4 degree of trim at rest. Not much but annoying. When she's done with her refit, I'll put 150 gals in each tank then use movable lead ballast to trim her to zero degrees trim. I consider this normal after 50 years and a major refit.

Peter

Bingo!! my solution for everyday boating. two 50# ingots wth barn door handles screwed to the top for ease of handling.

This quote is confusing and contrary to operations as I am familar with. In all of my boats, a common fuel line is in play from both tanks. My return line is tee'd to both tanks. I have never has an issue and am confused as to why I would save a pluged line in the mix. What are the odds? and then of not being aware were it to develop. O well, on to reading more on the subject.
.

Not sure if you are doing this but that crossover line is required to be closed when underwayAlso I would advise against running from both tanks at the same time with both returns open. Any flow issues and you could actually transfer all the fuel to one tank creating a very unbalanced boat. And maybe even a fuel spill. You should probably alternate every couple of hours.

 

[Cartouche]

A guess but if there is only one return line to one tank then all the return fuel will stay in that tank and cause a loss of fuel. The balance line may be needed to at least try to effect a balance.

When closing the balance line the return line should also be directed to the same tank you are drawing from or you could actually overfill the tank that the return fuel goes to and dump fuel out of the vent line. Don't ask how I know.

I looked for any mention of two return lines, one to each tank, with valves so the return fuel can be directed. If the fuel is not able to be directed to the tank being drawn form then you need the balance line.

Maybe a project for another day to correct.

If you go this route, directable return lines then you must ensure that you NEVER shut of the active one before opening the other valve or injector pump damage can occur.

The return goes to the starboard tank but even with the Cross over line closed the engine will still draw from both tanks

 

[C lectric]

The return goes to the starboard tank but even with the Cross over line closed the engine will still draw from both tanks

Yes the engine will draw from both tanks but with the crossover closed the return fuel will go to one tank only so that tank can be overfilled and overflow unless there are individual returns to each tank and both are operable or switched to the main draw tank. This can also lead to a list after a run.

Just be aware.

 

[twistedtree]

The return goes to the starboard tank but even with the Cross over line closed the engine will still draw from both tanks

And this is why you need to keep the cross over line open.


I too would check your vent lines. A low spot in a vent line that gets flooded with fuel from an overfill will block the vent and cause all sorts of problems. It's easy to test by opening the fuel fills for both tanks, turning them into vents, and see if they balance out. I had this exact issue with interconnected water tanks on another boat

 

[MurrayM]

And this is why you need to keep the cross over line open.


I too would check your vent lines. A low spot in a vent line that gets flooded with fuel from an overfill will block the vent and cause all sorts of problems. It's easy to test by opening the fuel fills for both tanks, turning them into vents, and see if they balance out. I had this exact issue with interconnected water tanks on another boat

Another reason to check is because it's the simplest to fix problem. I always try to start there when gremlins creep aboard our boat, because, well, it's the easiest and might save me a bunch of unneeded head scratching and labour.

Surprisingly often, it is the simplest fix that solves an issue.