Uneven Fuel Burn

F

FB340DA

New Member
May 20, 2019
12
Upper Chesapeake Bay
Boat Info
2005 340DA
Engines
Twin 5.7l Merc V-drives
hello, all. I have a fuel burn issue with my 340DA. It appears as if my port motor is burning around 1/4 tank more fuel according to the gauges and in reality after refueling it appears as if it’s burning around 3/16 of a tank. I know that the gauges aren’t perfect but should the port motor be burning somewhere between an 1/8th and a 1/4 of a tank more fuel?
 
Watch closely when you fill up. Compare the two tanks. It’s probably the tank sensor going bad. Your generator probably pulls from your starboard. That is why I say probably sensor issue. If the engine is running smooth...
 
Does your boat have Smart craft? Can you confirm that both engines are generally running at the same RPM? A couple of hundred RPM difference while cruising can use a lot of fuel.
 
Phasma said:
Watch closely when you fill up. Compare the two tanks. It’s probably the tank sensor going bad. Your generator probably pulls from your starboard. That is why I say probably sensor issue. If the engine is running smooth...
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Yeah I’ll be paying close attention to my gauges and how many gallons each needs at every fuel up for a little bit here. I don’t know if it’s a tank sensor issue because when I refuel the port is needing quite a bit more fuel to reach full than the starboard. I also never use the generator other than starting it up just to let it run for a little bit every now and then. Both engines seems to running very good so I don’t think there’s an obvious problem with the motor using more fuel.
 
amajamar said:
Does your boat have Smart craft? Can you confirm that both engines are generally running at the same RPM? A couple of hundred RPM difference while cruising can use a lot of fuel.
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Yes I have the smartcraft and I do pay attention to the RPMs. I always try to get as close as I can to a perfect rev match.
 
Is it possible that the port fuel tank on a 340 is a little bit smaller than the starboard? Is it possible that the port motor is running a little more lean without it really being obvious? Is it possible that a tiny difference in rpm’s could be causing a significant difference in fuel burn? Is it possible that uneven trim could be causing the port motor to burn more? I feel like the boat is trimmed right but maybe it’s slightly off. Or is it possible that all those things being just a little bit off could add up to a pretty decent difference in fuel burn for the port motor?
 
FB340DA said:
Is it possible that the port fuel tank on a 340 is a little bit smaller than the starboard? Is it possible that the port motor is running a little more lean without it really being obvious? Is it possible that a tiny difference in rpm’s could be causing a significant difference in fuel burn? Is it possible that uneven trim could be causing the port motor to burn more? I feel like the boat is trimmed right but maybe it’s slightly off. Or is it possible that all those things being just a little bit off could add up to a pretty decent difference in fuel burn for the port motor?
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on the earlier model 340's (1998 - 2003.5) one tank is 110 gallons and the other is 115 gallons....i believe the port tank is the 110 and the starboard is 115 because the genny pulls from this tank...

maybe your model is the same...

cliff
 
CliffA said:
on the earlier model 340's (1998 - 2003.5) one tank is 110 gallons and the other is 115 gallons....i believe the port tank is the 110 and the starboard is 115 because the genny pulls from this tank...

maybe your model is the same...

cliff
Click to expand...
Actually this is backwards. For some reason, Searay installed a SMALLER tank on the starboard (genny) side. At least that's the way my '00 340 is configured. I think it may be a weight distribution thing.
 
There are so many variables in fuel consumption that figure in. Current,wind,load,props,rotation, ect. No 2 engines are the same. If you get within .5 to as much as a gallon per hour difference can be normal. Any more than that and I would start to investigate.
 
I am having similar issues. My port engines is always more full than my starboard side. I believe its a sensor issue, they usually take about the same amount when I refuel. On the gauges it says my starboard side is always 1/4 below port side.
 
Electronic fuel tank gauges are about as reliable as Trump saying something intelligent. I'd top them all off until they stop taking full and record consumption from there. I use a manual system to record my fuel consumption based on distance/hours. Its not pretty but it works.
 
Old thread, but wanted to revisit to see if the OP found resolution? I have vesselview installed on my 2004 340da with 8.1 v- drives and find that my port engine burns 2 gph more than the starboard at ~3800 rpm. 2 gph seems pretty significant. Would really like to hear from other captains that have experienced this and what they found to be the issue.
 
One thing to keep in mind is that smartcraft uses a fuel usage algorithm/RPM from the computer rather than a fuel flow sensor. Not saying that the PCMs could or should be outputting different values per RPM, but they may be. As said before, take careful fill and refill data and see if it you can confirm the 2GPH delta.
 
I have twin Volvo Penta's. Had a shaft straightened and props tweaked this past winter. Based on my ECU data from the Fox Marine Gateways, my starboard engine consistently burns 0.6-1.0gph more than my port. I haven't felt a need to investigate as my running gear is good and it's a constant differential.
 
Cory Hart said:
Old thread, but wanted to revisit to see if the OP found resolution? I have vesselview installed on my 2004 340da with 8.1 v- drives and find that my port engine burns 2 gph more than the starboard at ~3800 rpm. 2 gph seems pretty significant. Would really like to hear from other captains that have experienced this and what they found to be the issue.
Click to expand...

Check to see if both engines get to the maximum RPM. One engine could be working harder than the other, needing more fuel.
 
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