Fuel Flow Meter

Project date: 2003



This project details the installation of a Standard Horizon Fuel Flow meter. The idea behind a fuel flow meter is to determine the rate of fuel consumption. This is essential information for boats that average 2MPG or less - because just changing the cruising RPM by one or two hundred RPM may result in a significant fuel consumption change. As well, the outdrive trim angle, and if you have them, trim tabs, all effect efficiency and fuel mileage. A fuel flow meter will allow these adjustements to be made for the most efficient operation.

Note:

The Standard Horizon FF41 fuel flow system installed here is a clone of the Navman 2100/NorthStar F210 Fuel Flow meters.

At gas prices what they are, a fuel flow gauge should pay for itself after awhile. Its a wonder why these are not considered standard equipment.

Another advantage is since you know how many gallons your fuel tank contains, and if you know the rate of flow, then you can accurately determine how much gas you have left. Most boaters know that fuel tank gauges are notorously inaccurate, so the fuel flow meter allows you to determine how much fuel you have on board.

The first step was to determine where to mount the gauge. This can be a problem in some boats, but fortunately, I had an extra 2in gauge hole in my dash, covered by a blank. The blank was simply glued on with hot-melt, and it was very easy to pop the blank off.

The meter, as received from the manufacturer has a black bezel. However, a chrome plated genuine plastic trim ring is available from the manufacturer. I used this ring, so it would match the rest of the gauges on the boat. The next step was to put the gauge in the panel and wire it up. I used the existing gauge wiring harness to do this, but it required using some adapter terminals.

The gauge manufacturer recommends using a filter prior to the sensor in their docmentation. They also recommend installing the sensor vertically, and to attach it to a rigid member, such as a bulkhead. I was going to have problems meeting these requirements - so I contacted the manufacturer's technical department.

After discussing the issue at length, I decided I could meet the spirit of the requirements with the installation, even though I did not follow all of their published recommendations. However, this is not to be done without consultation with the manufacturer's technical department.

To create a mount, I used a couple pieces of left over King Starboard and made a simple mount using cable ties. If you have never used Starboard, it works well with standard woodworking tools. The only problem I have found is that you cannot get any glue to stick to it.

I did not use a filter as the boat was a fairly new one, and constructed with a poly tank, so there would not likely be any issues with rust or other foreign material in the tank to clog the sensor.

While the manufacturer recommended mounting the sensor vertically, I was not able to do so without introducing some very sharp corners in the fuel line. About 30deg from horizontal was the best I could do. The tech support department recommended vertical mounting to prevent fuel from sloshing back and forth through the sensor with the boat at rest. While this would not affect the GPH rating, it would affect the total fuel burn. However, I felt the 30deg angle was sufficient to prevent this from occuring.

I need to state that I didn't like the construction of the fuel sensor. I thought is was rather cheap looking. And I could not use the included hose clamps as my fuel line was too thick for them to work. So I used the familiar stainless hose clamps. When I attempted to tighten the clamps, I actually crushed the nylon hose barbs on the sensor!

Compare this fuel sensor to FloScan's aluminum bodied sensors with brass barbs and I think you'll agree some improvement could be made here. However, I was able to get the fuel lines attached without any leakage from the fuel sensor; I just think the sensor construction was on the cheap side.

Caution:

If you use stainless hose clamps, be sure you do not overtighten them, or you will crush the nylon hose barbs.

Wiring is covered in the manual so I will not elaborate a lot here. Essentially two wires from the gauge go to the power connection, and a 5 pin cable from the power connection to the paddlewheel fuel sensor.

The initial operation test was a real eye-opener. I was able to vary the boat's speed, and watch how the fuel flow differed. It is pretty amazing that just a few hundred RPM can have a significant impact on how much fuel is used. And.... to see how thirsty the engine is at Wide Open Throttle! That realization in itself is enough to keep the throttle backed off the stops.

      

The left photo shows total/trip fuel used, while the right photo shows the current GPH fuel rate. Since there is no provision for connection to a GPS signal, this instrument is not capable of displaying MPG information. As well, there is no provision to enter the tank size, however you can enter the gallons on board after fuel up, and the instrument will calculate fuel remaining.

However, if you can believe the speedometer (or use GPS speed), we're travelling 26.5 MPH and burning 11.6 GPH; which means we're getting 2.28 MPG. Not bad for a 26ft cruiser. The advantage of a fuel flow instrument such as this is that you will come to realize that a slight adjustment of engine RPM or boat trim (trim tabs and/or drive angle) will vary MPG by a significant amount. You can now trim the boat to maintain the best fuel economy for any sea conditions.

If you need additional data, such as direct readout of MPG, consider the Lowrance LMF-200 or LMF-400 units. These are actually NMEA-2000 multi-functional display systems with a network of sensors that you can display, including fuel flow, tank levels, trim tab settings, and dozens of other data - providing you wire in the proper sensor. The LMF units use an almost identical looking fuel sensor, so installation practices discussed here will apply.

 

 

Note:

Since the publication of this article, the most popular methods of fuel flow measurement are either NMEA2000 networked instruments (such as the Lowrance LMF instruments), or via ODB diagnostic port. You will not find many stand-alone fuel flow instruments these days. The FloScan products being the exception.

 

 

  

 


Home    Return