Unequal Fuel Usage in my 2005 340 Sundancer

[Sea Ray Rob]

I have noticed that my Starboard engine uses a lot more fuel then my Port engine during normal operation and cruising. I have not used the generator during the last 2 fill up's and I always put about 15 gallons more in my Starboard side tank in case I need the generator. I have noticed each time that by the time I get to 1/4 tank on each side I am always about 10 gallons less in my Starboard then in my Port tank, so it's used up about 25 gallons more fuel than the Port side I pay very close attention to my RPM's and make sure they are always synced up while running. :huh:

There is no leak in the tank. I have twin 8.1L 4946 Horizon Mercruiser Gasoline engines with only 180 hours on both.
Has anyone had this issue and what did you find was the problem/cause?
I am about to call the marine mechanic but wanted to reach out to the members before doing that in case it's something easy.

 

[Island Time Buffalo]

My former 310 and now my 380 both burn gas unevenly, but a 25 gallon differential does seem a bit high. Don't want to presume anything, but are you sure you are starting at even points in both tanks? In my years of boating I've never met a gas gauge that was anywhere near accurate. In my case the only way to ensure even starting position is to fill them both (carefully listening for the end of tank gurgle) and then later also refilling to the top to make your measurement. I usually end up within 5-7 gallons of each other without the genny running.

But at any rate, because of counter-rotation and other factors like trim and conditions, dual engines will not likely ever match consumption 100%.

 

[Tomco]

We have a 2004 340 with the 496 and BIII drives - my starboard engine does consume a little more fuel than my port side - about 5% difference over a full tank of fuel. So, that would be about 5 gallons. Genny use is not material in our case. I used a Quicksilver 2 fuel additive this season and find both engines run smoother - don't think it has any effect on fuel economy. It has been 3 seasons since the plugs have been changed, but the engines run so well I'm not in any rush to change.

Will be following the thread to see what inputs you receive.

 

[fdough1]

Funny but I just started to notice this on my 2007 340. I chalked it up to overnight generator use on the hook. Maybe a bad assumption.


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[Sea Ray Rob]

Thanks, I will try that on my next fill up and monitor it between consecutive fill ups. If there is one thing I have learned is that gauges on boats never tell the full story.

 

[Sea Ray Rob]

Tom, I do use a high quality fuel additive and the engines run beautifully, which is why this is such a mystery? I still have a few things to try before calling in the mechanic.

 

[Kreole Kid]

Might have something to do with the rotation / counter rotation of the props?? I will follow as well, should be interesting to find out the culprit.

 

[bankyf]

I was once told, but have been unable to locate any more information, that the 340 needs to have one tank filled before the other to get both completely full. If you fill one side first it causes the boat to list in a way that the other is not able to be filled completely due to the location of the fill hose on top of the tank. I just can't remember which side it is that needs to be filled first.. Perhaps this could have something to do with it?

 

[KevinC]

I noticed something similar on my first longer run this on my new to me 2004 340. I will have to review my log but I first noticed the starboard engine was always running a couple of GPH higher on the smartcraft gauges than the port. At the end of the trip I did see a consumption difference based on the smartcraft fuel used and tank gauges. On the trip there was no generator usage either. I was beginning to question if this was normal too.

-Kevin

 

[Sea Ray Rob]

Interesting, I will ask around about that.

 

[bankyf]

Another thought - The props on these boats are a different pitch between port and starboard to account for the slightly different gear ratio of one trans running in reverse. Perhaps one combo of ratio/pitch is slightly more efficient than the other.

 

[bankyf]

From the Prince William Marina service records on my boat -

"stbd fuel gauge incorrect by 30 gals. *** Boat was designed to fill from stbd side, when port side is filled first, a list causes stbd side not to completely fill"

 

[Sea Ray Rob]

I filled up last weekend starting with the Stbd side first and then doing the Port side, we'll see what happens when I need fuel again.

 

[howie58]

I realize this is a old post, but I have a 99 340 and the fuel tanks are not the same size, meaning one tank holds I think between 5 to 10 gals more. I don't remember which side is bigger. Probably the bigger tank is for generator hook up.