mercruiser smart craft flow meter

[srdancer90]

I first used the flow meters the other day, I noticed a difference in the flow rate for each engine, the starboard side used about a gal more than the port at near the same rpm.My question is how accurate are the smsrt craft flow meters?
2004 320 DA 5.7 350 mag mie

 

[SevenTeas]

You said near the same rpm. If it was higher, more fuel. If lower should be less fuel.

A gallon more over what period of time?

 

[srdancer90]

port 3400 rpm 14.6 gph starboard 3300 rpm 13.5 gph

 

[Rxflyer]

Was the genset running ? I know mine draws from the stbd tank. What I'm not sure of, is whether or not the flow meters add that (roughly 1 gal/hr) to the stbd flow. Just an idea, and hopefully one or the gurus can answer that, too.

 

[Henry Boyd]

Keep in mind the 'flow meter' information from Smartcraft is not really based on actual fuel flow. In other words, Smartcraft is not physically measuring the amount of fuel flowing through the fuel lines (unlike things like a FloScan). Smartcraft, or more correctly, the ECM is calculating the amount of fuel being consumed based on the data it is collecting, and the settings it has set to run the engine.

I have been keeping track of fuel consumption for the past couple years and have found that SC will say the boat has used X gallons and when I go to fill it up it reads about 110% X gallons. Since I usually wait until the tank is at about 1/4, there is no way there is 7-8 gallons of fuel in the fill pipe.

The other thing I have noticed is that flow rate is affected by engine load. I can adjust flow rate (as an improvement) for a given RPM by adjusting the drive trim slightly. Improving the rate by a 1- 1.5 GPH can be done very easily.

So between the potential inaccuracy of SC's 'estimated' flow rate, and the fact that there may be very slight/minute differences between your transmissions and props, the roughly 7% difference you noticed may just be the inaccuracy of the system.

Henry

 

[Dave S]

Smartcraft measures the flow rate based on the number of times and duration that it pulses the injectors. Mine is not accurate either and is usually off about 3-4 gallons on my 84 gallon tank when it is filled up at about 1/4 remaining. I do have to be careful though because my remaining gallons is overstated meaning that Smartcraft is underestimating my consumption.

Dave

 

[Bucit]

My port motor always shows it burning .5 -.75 more gallons per hour at the same RPM and my fuel gauge on the SC shows I have less fuel than I actuall do. when I fill up and the gauge syas I have 50 gallons left (and it should take 50 gallons to fill her up) it will only take about 38-40 gallons for fill up. I agree, these gauges are only tools for us to estimate but the information should never be 100% trusted.

 

[Henry Boyd]

Scott,

That's a good point. I zero out the trip computer at the end of each day, but not at fill up. So for all I know the inaccuracy is in the tank calibration/fuel sender and not the fuel consumption calculation.

How well does the cumulative gallons burned match up with gallons added?

Henry

 

[Dave S]

Wrongo! Sorry Dave, but the gallons remaining that smartcraft shows is from the fuel senders in the tank, not based on gallons burned. Which means that it is basically worthless, as we all know that the senders in the tank are very inaccurate.

What I have always done, is take the gallons burned, shown by smartcraft, and done the mental math to calculate how much fuel is left. It's unfortunate that SC instruments don't take the senders out of the equation and just deduct fuel burn from X amount of fuel, but I suppose they don't since it would take user input to remember to zero the readings at each fill up. (like we do in the jet)

I am not sure you are correct on that Scott.

The only reason I say this is that my fuel numbers (used, remaining, gph, etc) also show on my Smartcraft interfaced Navman Chartplotter. On a few occasions I have neglected to turn on the chartplotter when running the engine and in that situation the Chartplotter always shows less consumption and more fuel remaining in the tank than my Smart Craft instruments show.

Dave

 

[Dave S]

Hey, wait a sec....I'm still waiting for the pictures of your boat so that we can settle who's is more shiney.

Scott

You mean you don't remember this picture from the now famous (infamous) BoatTest.com article on Shurhold products? :grin:

 

[srdancer90]

Thanks for all the info. 5-7% is not too bad an estimate. The reason for the post was to determine if I really used the gas that my tanks say is left in them. I ran a two(2) hour round trip in the early season, full tanks both sides 4 people 3600 rpm both ways( on aver) According to my fuel tanks it showed that I used 100 gal ( 50 per side ) friends say that this is impossible. So I used the flow meters on a short 4 mile rum varying the rpm at 4000 the boat uses approx 17 gph at 3500 13-14 gph, so I could not have used 100 gal a 2 hour round trip cruise.the gas meters on the smart craft must be innacurate.I may add that I contacted Mercruiser tech to help recalibrate the digital read outs. After all was said and done it still showed 50 left on both sides. I am at a loss as what to do about the accuracy of the tank readings.
2004 320 DA t 5.7 MPI MIE