Ok for gas tanks to read slightly different?

Nick70

Active Member
Apr 20, 2016
206
New England
Boat Info
2006 Searay 260 DA 496 mag
RAYMARINE stuff.
Engines
496 Magnum
Bravo III
just wondering..we filled up on Saturday. Starboard is now reading slightly lower than port.
Burned approximately 50 gallons since fill up.
2009 330 Sundancer
I don't know but had thought they were connected and would read the same?
 
They may or may not be connected. On my 370EC, which I just sold, there are valves that allow either engine to pull from either tank or both. Also, my generator pulls from the starboard tank, so all else being equal, it will have less fuel in it if the generator has been running. Finally, I have found gas gauges to be notoriously only an estimate of what's in the tank. Underway, my tanks almost always looked full!
 
On my 320 the tanks are not connected. To make matters interesting, the gauges do NOT track linearly or in sync. The starboard engine appears to go down faster. It can read almost E with a 1/4 tank still in it. Makes me happy at the gas pump but makes for some more stressful rides than necessary back to port!
 
My current boat has valves for the motors to draw from either motor and the genny draws from the starboard tank.
My old boat didn’t have the valves. Each motor drew from it’s own dedicated tank.
Two things they had in common:
1. The motors never burned the exact same amount of fuel on either boat.
2. The fuel gauges on both boats were inaccurate.
 
They operate on electronic sensor versus a float. After filling up and running a short while my starboard many times reads 1/2 full while Port reads full. DO NOT trust the gauges. I keep a log of when I filled and hours run so I know when to re-fuel. My advice is keep them pretty full.
 
One more hot tip - I recently learned through the 340 thread that not all boats have two tanks that are the same size. Mind boggling....but confirmed with Sea Ray parts manuals even.
 
They operate on electronic sensor versus a float. After filling up and running a short while my starboard many times reads 1/2 full while Port reads full. DO NOT trust the gauges. I keep a log of when I filled and hours run so I know when to re-fuel. My advice is keep them pretty full.
Thats the way mine is. The total fuel left seems to be pretty close though
 
One more hot tip - I recently learned through the 340 thread that not all boats have two tanks that are the same size. Mind boggling....but confirmed with Sea Ray parts manuals even.
You are correct. My old '89 340da had 2 tanks. Port was 72 gallons and the starboard was 80. To compound the issue, the gen pulled from the port tank.
 
My '07 310 DA has been using more fuel from starboard than port since I got it, no cross-feeds and the genny runs off the port tank. I noticed it at the gauges first and then began keeping track of fuel consumption at the pump for each tank individually, and sure enough I've been burning about 30% more fuel in the starboard side.

I finally got a second mechanic to look at it and my starboard fuel regulator needs replacing, its pushing too much fuel.
 
Do yourself a favor and invest in some kind of fuel flow monitoring system. They are reasonably priced for gas motors, easy to install, and can pay for themselves in a season or two if you keep an eye on what you’re burning in real time.
IMHO: Floscan is the best. I had a Garmin NMEA 2000 network and MFD on my old boat so I installed their GFS 10’s they’re fairly inexpensive and should be able to be used with any NMEA 2000 network.
You enter the info about your tank sizes, the GFS 10’s monitor what you burn in real time, and the computer lets you know how much you have remaining in each tank and range at current speed.
I found them to be accurate to within 2 or 3 percent when I filled up.
 
I have 2 150 gallon tanks with selector valves.

When I got the boat, the gauges were all over the place and fortunately the sending units were very easy to access.

I replaced them both and carefully set up the rod/float arrangement so that they were identical. I left them an equal distance from the tank bottoms leaving a 20 gallon reserve once the gauges read empty.

I have total faith in them, but rarely get under 1/4 tank. Occasionally I’ll close a valve for a short time to burn out of the heavy tank to equalize.
 

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