Twin fuel tanks/ uneven usage

B

Boldinb

New Member
Sep 26, 2021
6
Boat Info
1999 310 Sundancer
Engines
Twin 350 mag
Just bought 1999 310 Sundancer. twin 350 mag, twin 100 gal fuel tanks. Fueled up and both gauges showed between 3/4 and full but we’re quite even. Seller told me gauges would “even out”, suggesting tanks are connected.
4 hour cruise home today. Stbd gauge ran almost to dead E, while port gauge showed over 1/2. Couple questions:
Are tanks wholly separate or connected, meaning will both engines run from either tank or is each tank dedicated to that engine?
Any help appreciated.
 
Do you have/run a generator? My 48 had separate tanks and one would feed the generator causing uneven usage.
 
There is no "evening out" setup - the tanks are not connected by a common hose. However, you may have a crossover valve to run either engine off either tank. You might not have that on a smaller Sundancer, though. Check your manual or just look in the bilge - follow fuel lines if you need to. The lines may go direct to a tank - which would mean there isn't a crossover.

If the engines were running well (you can check/compare spark plugs, if you want), most likely, the tanks just weren't filled equally to begin with. Fill till you hear a gurgle - don't base it on the gauges.
 
Where the engine in sync? You should have a synchronizer gauge, which allows you to make sure both engines are running at exactly the same RPM. The RPM gauges themselves may not be accurate enough to use for ensuring sync, and thus trying to match them using RPM gauges is not as accurate as using the sync gauge. Sometimes the throttles need to be offset slightly given linkage - which is where the sync gauge comes into play. If the engines are not synced then your fuel burn can be off. Even if they were not in sync, I cant see it explaining that much of a fuel discrepancy unless you were dramatically off by 1000+ RPM.
 
There is no crossover. The Sea Ray gages/senders are notoriously inaccurate. I'm running a NMEA tank sender which eliminates the gage half of the equation. I'm thinking of replacing the senders with a Maretron ultrasonic sender, once I get a chance to measure my tank height.
 
Fill both tanks back up. I bet they are with in 5 gallons of each other. Hence the gauge or sensor is wrong.
 
Bear Paws said:
Do you have/run a generator? My 48 had separate tanks and one would feed the generator causing uneven usage.
Click to expand...
Thank you bear, there is a generator but it wasn’t run at all so that wouldn’t be the culprit.
 
Lazy Daze said:
There is no "evening out" setup - the tanks are not connected by a common hose. However, you may have a crossover valve to run either engine off either tank. You might not have that on a smaller Sundancer, though. Check your manual or just look in the bilge - follow fuel lines if you need to. The lines may go direct to a tank - which would mean there isn't a crossover.

If the engines were running well (you can check/compare spark plugs, if you want), most likely, the tanks just weren't filled equally to begin with. Fill till you hear a gurgle - don't base it on the gauges.
Click to expand...

Got it, thank you for the info!
 
Thanks for the info and link. I count myself as “fairly mechanical”, looks like something I can handle myself. Appreciate the info
 
markrsimon said:
Where the engine in sync? You should have a synchronizer gauge, which allows you to make sure both engines are running at exactly the same RPM. The RPM gauges themselves may not be accurate enough to use for ensuring sync, and thus trying to match them using RPM gauges is not as accurate as using the sync gauge. Sometimes the throttles need to be offset slightly given linkage - which is where the sync gauge comes into play. If the engines are not synced then your fuel burn can be off. Even if they were not in sync, I cant see it explaining that much of a fuel discrepancy unless you were dramatically off by 1000+ RPM.
Click to expand...
markrsimon said:
Where the engine in sync? You should have a synchronizer gauge, which allows you to make sure both engines are running at exactly the same RPM. The RPM gauges themselves may not be accurate enough to use for ensuring sync, and thus trying to match them using RPM gauges is not as accurate as using the sync gauge. Sometimes the throttles need to be offset slightly given linkage - which is where the sync gauge comes into play. If the engines are not synced then your fuel burn can be off. Even if they were not in sync, I cant see it explaining that much of a fuel discrepancy unless you were dramatically off by 1000+ RPM.
Click to expand...
There is a sync gauge, and I made sure I was synced. Occasional bump one side or the other but never long enough out of sync for that to be the culprit. think I have it narrowed down to sending unit or gauge. Thanks for the info
 
Lazy Daze said:
Before you look into "issues", fill up like I mentioned above. There may not be an actual issue.
Click to expand...
Yep, got it. Will fill up next time up and go from there. we did put 70 gals in each tank before the trip so I know we started each tank no less than 3/4 full, and I’m confident we couldn’t have burned that much on the trip was was right about 80nm. Thanks again
 
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