See full version: How Fuel Gauge Works: Analog and Digital Mechanism
In the dashboard, we can also see a symbol of a pump with an arrow that indicates the direction and position of the inlet. It is called a Moylan arrow. It helps drivers to park in the correct position in the petrol pumps. This was first implemented in Ford cars. Many people still park their vehicles in the wrong direction and we can see many such funny videos on the internet. [links]
Modern vehicles also work with the same principle. However, they have a microprocessor to read the resistance or current in the circuit. They can also compensate for the shape of the tank and calculate the volume of fuel remaining very accurately. The microprocessor can also ‘dampen’ needle movement. This means that your fuel gauge doesn’t swing abruptly as you turn corners or climb hills, which sloshes the fuel in the tank, along with the float, exposing more of the rod. These things can cause errors in reading and indication.
When the oil level drops then float also drops. The float is connected to a side or arm of a potentiometer. This changes the value of the current in the circuit. Usually, the current is lower when the level drops and when the level is up, the current is also up. It means the resistance (ohm) value is higher when the oil level drops. Thus as the vehicle moves and consumes oil, the level changes and so does resistance and current. Then the indicator in the dashboard measures the current of the circuit. The calibrated dashboard then gives us the amount of fuel in the tank. This is basically how the analog fuel gauge system works. here
Nowadays companies are manufacturing vehicles with digital speedometers and safer fuel gauges. These are much more accurate and suffer less from breakdowns. The maintenance cost is less and life is also longer These also don’t have the chance of having broken dials. We can see people with cars that show fuel gauge reading incorrectly and the indicator is stuck in full or empty. The digital ones don’t break easily. There is higher accuracy and it is best for everyone and mainly consumers or drivers. here
Normal gauges use float and flow of electricity in the potentiometer. This is not considered safe ideally as there can be a fire hazard. Now there is a new system of level sensors that puts the sealed system and keeps the electronics outside the tank. In the magnetoresistive fuel gauge, there is a magnet in the float arm. Its position is transmitted from the magnetic field when it moves inside the tank due to the change in level. It has very good accuracy, is very safe, and changes some mechanism of how traditional fuel gauges work. The basic principle is magnetoresistance for this type of sensor.
The market is now moving towards battery-powered Electric vehicles (EV). But still many vehicles operate with fossil fuels such as diesel, petrol, and gas. They all rely on indicators for various measurements. Fuel gauges operate on the electrical resistance principle with a float attached to a metallic rod as the internal ‘needle’. The basic mechanism depends on a potentiometer or variable resistor. A float is in the fuel gauge sender unit. It is connected to the resistor using an arm. The change in current is then read by the dashboard’s indicator and finally, we get the reading.
When digital fuel gauges were first introduced in the late 70s, consumers began to complain that their cars were getting unusually bad gas mileage. When the manufacturers tested these claims they found that, not only did the cars achieve the posted mileage numbers, but the new digital gauges were recording gasoline levels more accurately than analogue gauges ever could. [links]
Many people rely on fuel gauges to make sure they have enough gas in the tank to get home, and some drivers calculate fuel economy by watching the meter. However, as a result of a few scientific studies on the subject, the jury is still out on whether these gauges are truly accurate. The design of certain types of digital gauges means that in special cases, they will either over- or under-exaggerate the amount of fuel left in the tank.
With digital gauges, drivers could witness every gallon of gas being consumed, which meant that no sooner had they filled their tank than would it begin to deplete itself, causing concern among some vehicle owners. Clearly, something had to be done. The designers went back to the drawing board and came up with the perfect solution. In previous designs, the gauge would count down the number of gallons until empty -- 20, 19, 18, etc. The redesigned gauges skip every other number to slow the rate of gas consumption by all appearances. These same gauges will also compensate and recalibrate themselves when they are driven or parked on an incline so as to remain consistent. The effect was profound, and as tanks stayed “full" for longer, the complaints evaporated.
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And gw204, thanks for the suggestions about the fuel flow gauges. I had FloScans on my Krogen and they worked great, but I can't see the cost for a near-offshore rig. My policy is not to leave for beyond 10 miles without a full tank.. here
Seasick, sounds like you are experiencing the same readings as I am. Recently I showed 2 bars most of the time, occasionally flashing up to 3, and when I filled up it took 46 gallons. Since 2 bars is 1/4 of the 8 bars on the gauge, I expected to put in around 60 gal. Not so. here
Is this normal or is the sender possibly bad?
Thanks for the comparison. [links]
I was hoping that the gauge would be a little more accurate but it sounds like it is what it is and I'll have to figure out what it really means. For now, 2 bars = 30-35 gal remaining. [links]
However, you should be able to get a flow sensor that works with your Raymarine unit. That would be the most cost-effective option, now that I think about it. With a fuel flow readout, you can fine-tune your throttle and trim setting to optimize fuel economy, quickly recouping the cost of the sensor. Even a separate Floscan unit would offer a quick payback if you use a lot of fuel.
I know for sure that the Raymarine unit is NMEA 2000 compatable and it has the digital instrumentation built in, which includes a fuel gauge. I was told by the guy at the marine store that my engine was not NMEA 2000 compatable. Is that wrong? I would love to have that digital instrumentation on the raymarine unit working. more
2if,
I just checked out your Raymarine unit and it can read NMEA 2000 data. You may want to contact Raymarine, or look through your owner's manual, and see if it will read fuel levels/fuel usages, then see if you can use the Lowrrance fuel module EP-15 (http://www.lowrance.com/upload/Lowrance/Documents/Manuals/EP-15FluidLevel_0154-371_100405.pdf) to display your fuel level on the Raymarine unit.
Just because you have a digital readout does not mean you have accuracy. The fuel sender in the tank has that job. Replace the sender with one of the more accurate versions (no float arm) and go boating.
Floscan is one of the standard-bearers. But as you can see, they are quite pricey. Installation is fairly easy- a sensor is installed in the fuel line and wired to the head unit, along with the usual power leads.
You would be better served by a fuel flow meter, IMO. more