Fuel leveling issues

[PatrickF]

My 1993 42 Classic has started to return all of the unused fuel only to the Starboard side tank. I believe that is what is happening. After running several hours the starboard tank is full and the port tank is significantly lower. Previously they would drop at the same rate. After sitting overnight the tanks will balance and repeat the next day. I’m not in a location I can remove the return lines to see if they are clogged. So, I tried to close the supply valve on the port tank to only use fuel from the Starboard tank and that stalled the port engine. Should both engines, I have Cat 3116s, be able to run from one tank? From the flow diagram I assumed yes but that’s not what happened. Just trying to determine if I have two problems or one.

 

[READY]

A shot in the dark but worth checking your tank vents. That could contribute to slow balancing. I don't know how your fuel manifold is set up but most boats can be configured to run either engine from either tank.

 

[DrissZougari]

it sounds like both engines were pulling from the Port Tank only!

 

[mahal]

My guess is that the port tank was the only tank supplying fuel to both engines. I would also guess that the starboard engine would have stalled too if you let it run long enough with the port tank valve closed. If this is the case, there’s something going on with the starboard side fuel system. A blocked line, vacuum leak or, as Ready suggested, a clogged vent.

Edit:
DZ beat me to it as I was typing.

 

[PatrickF]

As suggested, the starboard supply line between the tank and manifold was blocked. This has been corrected. Vents were not blocked. Would this explain all of the return only going to the starboard tank? I guess we will go for a short test run to find out.

 

[READY]

Do you have a selector to direct where the return fuel goes? On my Hatteras with Ford Lehman 120 engines it returns all fuel to only 1 tank. But the return is only about .25gals per hour so not a challenge to manage. So it could be your boat is plumbed to return to only the starboard tank. Glad you found and were able to correct the umbalance problem!

 

[mahal]

How do you know that both engines return fuel to only the starboard tank? Have you removed the return line to the port tank and saw no flow while the port engine is running.
If the return issue is just a hunch, I would guess that by clearing the obstruction on the starboard fuel line, your fuel leveling issue has been solved.

 

[READY]

Best bet is to just trace the return lines from both engines to be sure. I believe the OP said no crossover line between tanks but has been awhile since I read the early posts.

 

[rgano]

I ran my GB42CL's engines with the crossover valve between tanks closed and the engines only drawing from and and returning to their respective side tanks to prevent a bad-fuel related stoppage of both engines. The tanks could not equalize that way, but they never needed to unless the generator had been run a lot drawing only and returning to the stbd tank. You should be returning fuel from the engines to the tank on their respective sides.

In my GB, the equalizing line was separate from the supply lines to the individual engines, and if you shut the supply valve to either engine, it would shut down. Sounds like your GB is similarly set up. My Mainship's fuel supply is teed off of the cross-connecting hose, and I must close both port and stbd supply lines to starve the single engine. You are NOT apparently set up that way. Draw you fuel supply out do be sure and do indeed check the vents for mud dauber clogs.

 

[PatrickF]

Just following up, I did have a clogged line from the starboard tank and supply manifold. I’m not sure why this affected the return, but everything seems to be working correctly after a three hour test run this weekend.

 

[rgano]

Just following up, I did have a clogged line from the starboard tank and supply manifold. I’m not sure why this affected the return, but everything seems to be working correctly after a three hour test run this weekend.

Hmmm. Begins to look like a good tank cleaning is in order.