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Fuel Management:
Installing a FloScan Fuel Monitoring System

Lee A. Richards, Ph. D.

My GPS says that it’s 22 miles to Devil’s Creek. The fuel gauge reads right around a half of a tank. Lets see, it is 35 miles back to the ramp. If we keep going, that will be a total of 79 miles. Last time I filled up the boat, I figured that I averaged around 12 gallons/hr. But I was fishing a lot that day, lots of stop and go. Then there was the short bursts to WOT when we ran that skinny water. How much fuel would I of burned if I would of just cruised along at a nice steady speed? Can I make it to Devil’s Creek and back with out running out of gas?

This is a scenario that has played out for me many a time on the river. How much fuel am I actually burning? How much have I burned up to this point? Sure the fuel gauge says ½ tank. But is that 50 gallons or is it 30? My fuel gauge has been somewhat suspect at times. It always seems like the last half goes much faster than the first. After you have owned your boat for a while you get a pretty good feel for how far you can go on a tank of gas. An old river rat knows that he can make it from his home ramp up the river to the third bridge, do some fishing then make it back to the truck with a quarter tank of fuel to spare. But what about those times when you are exploring new places? What about the unexpected time you spend idling, waiting for another boat to make it through an especially tricky spot on the river? You never really know exactly how much fuel you are burning at any one moment, or even how much fuel you have burned up to that point.

I recently tackled this issue by installing a FloScan Fuel Monitoring System on my boat. Now I have instantaneous fuel flow readings, I know exactly how much fuel I have burned since I last fueled up, and I can optimize my cruise speed to get the absolute best fuel mileage from my boat.

FloScan Instruments offers a fuel monitoring solution for most any boat, from outboards to inboard diesels. The 5500 series will display fuel consumption in gallons/hour and total fuel consumed since your last fill up. The 7000 series has an all digital readout, including a digital tachometer, hour meter, GPH readout, and fuel totalizer. The 9000 series has all the features of the 7000 series but it can be interfaced with a GPS to give you actual miles/gallon.

I chose to put a FloScan 9000 series in my boat since I wanted a digital tachometer and thought that it would be handy to get instantaneous MPG readings while on the river. Getting the 9000 over the 7000 costs a little bit more money, but I figured that it would be worth it to get instantaneous MPG readings. Calculating MPG every time you increase or decrease the throttle setting could get tiring after a while.


Installation was rather simple. I am no electrical genius when it comes to wiring, but there is a very nice wiring diagram included with the instrument that even I could follow. My boat has a fuel injected KEM 383 in it, so two fuel flow sensors were needed. One for the feed to the fuel rails and another for the return line back to the fuel tank (Be sure you get the model that fits your application, a carbureted boat will only need one fuel flow sensor). Having 2 fuel flow sensors and a GPS interface makes installation slightly more difficult but still not out of the realm of your average boater. If you can strip a wire for crimping and read a wiring diagram, you can install a FloScan.

When my FloScan arrived, I was surprised to find that almost everything that I needed for the install was included. There were ample wire connectors, fittings, and even thread sealer was included. You will need several different colors of 18 gauge wire in 20 to 30 foot lengths (depending on the size of your boat). You will also need 4 barbed fittings to attach the fuel flow sensors to the fuel lines as well as some hose clamps to insure that there are no leaks in the connections. You will also need a momentary on/off switch for the totalizer and a toggle switch to switch from GPH to MPG if you have a 9000 series. I ordered both switches from FloScan but I suspect that you could get them cheaper from an auto parts store. Other than those few items mentioned above, all the necessary hardware was included. Of course you will need wire strippers/crimpers, a couple of wrenches, and a heat gun for the shrink fit tubing included with the fuel flow meter.

Physical installation of the flow sensors was straight forward. The kit comes with pulsation dampers that need to be inline with the fuel flow sensor (for my application, it could vary depending on your fuel system configuration). The directions showed that they needed to be at least 12 inches from the fuel flow sensor, but the technical service department at FloScan assured me that it would be ok to attach them directly to the flow sensors. Doing so eliminates several connections that would otherwise need to be made, not to mention another break in your fuel lines. The important factor to consider when placing the flow sensors is that the fuel must exit the sensors then travel uphill to the engine or fuel tank. This is to insure that the flow sensor always remains flooded with fuel. It is also important to maintain at least 12” between the each flow sensor and the fuel rails (or carburetor in the case of a carbureted engine). Once you have chosen proper locations for the sensors, it is a simple matter of cutting your fuel lines in the proper locations, (make sure you are positive this is where you want to put them, as fuel lines are expensive) inserting the sensors and tightening up all the hose clamps (I used 2 small hose clamps at each connection). If the sensor is able to fit in the proper orientation (it must be pointing straight up) you can also attach the inflow sensor and pulsation damper directly to your fuel filter (not your water separator mind you), if there is more than 12” of fuel line between the filter and the fuel rails. By attaching the flow sensor to the fuel filter you will eliminate the need to cut your intake fuel line. I was not able to do this in my application however, since there was not enough clearance for the flow sensor and pulsation damper to fit between the port motor mount and fuel filter on my engine.

Once you have installed the flow sensors it is time to turn to wiring. The instrument (9000 and 7000 series) will directly replace your tachometer. It is the same size as a standard tachometer so all you have to do is remove the old tachometer and pop the FloScan in. It is a good idea to save the back side bracket from your old tachometer, as no bracket is included with the FloScan. From here on out it is a simple matter of following the excellent wiring diagram that is included with the instrument. Go slow, double check all of your connections and make sure that you aren’t missing anything. Try to run all the wires from the engine compartment to the front of the boat in an orderly manner. It is very helpful to color code the wire so if there is a problem it is much easier to trace individual wires from the instrument to the engine compartment.

Calibration is really simple and just amounts to filling up your tank then burning about 20 gallons of fuel, then checking the FloScan totalizer versus the numbers you get after refueling. It is a good idea to use the same pump each time you fill up the boat for consistency. There are three calibration dials on the back of the instrument one for the tachometer, one for the totalizer and one for idle fuel consumption. There is a chart in the instructions that relates the amount of horsepower that your engine is rated for vs. the fuel consumption rate at idle. It is important to keep in mind that this chart is for a no load situation. I.e. a boat idling in neutral gear. We never have a no load situation in our boats since the jet pump is always moving water. For my motor, the chart listed a flow rate of .5 to 1 gallon/hr for idle. The tech folks at Floscan recommended that I use a flow rate of 2-3 gallons/hr considering I have a jet unit. I speculate that if you have a Hamilton 212 like I do, the fuel consumption at idle is going to be a little higher than if you have an American Turbine or 3 stage jet unit. My reasoning is that the 212 moves quite a bit more water at idle than some of the other units, thus the motor is under a bigger load and burning more fuel.

Fuel Flow!

Well how does it work? I couldn’t be happier with the operation of the unit. After a couple of tanks of gas and some really easy calibrations, I am in business. I can tell in an instant how much fuel I am using and really wean the throttle down to get maximum fuel economy. Before installing the FloScan, I would choose my cruise by feel. You have heard it as many times as I have “the boat feels like it likes to cruise at 3200 RPMS”. Now, I don’t feel, I know where I should cruise for any given situation to maximize my fuel economy. With the price of fuel being so high, I figure that I can pay for the flow meter with fuel savings in just a couple of seasons. The fuel totalizer is a real live saver in my opinion. No more between 1/3 and ½ tank guestimations. Now I know that I have burned X number of gallons so I know exactly how much fuel is in my tank. The digital tachometer is cool too. I like knowing exactly the RPMs that I am running. Before I figured my top end was somewhere around 3800 RPMs, now with the FloScan I know it is exactly 3850 RPMs when it is cool out. I actually noticed that the RPMs drop off a little now when the air starts to heat up, a change that was imperceptible with my old analog tachometer.

Next time I am out on the river, the situation may play out a little differently than before. It is 22 miles to Devil’s Creek and 35 miles back to the ramp here. I have been getting exactly 3 MPG cruising and I have exactly 35 gallons of fuel left. Lets go!

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