We usually see fuel gauges in cars and motorbikes. Fuel gauge gives data about the fuel level in the tank very accurately. Have you ever wondered how this gauge works and always gives us a proper reading?

The fuel gauge is a simple device. As a rule, it does not even indicate the amount of fuel in litres (or gallons); because all that is needed to alert, the driver is the amount of fuel relative to the tank capacity.

Photos: Mile’s End Motors Vancouver

In this case, there are only two main symbols on the fuel gauge – F for full and empty E. There is also a “middle or central” marking to show some half the tank. Sometimes 0-1/2-1 may be calibrated in place of E-central-F respectively. The litre contains important but accurate quantum information for driving, and even if someone is looking at their car’s FC (fuel consumption), the information is unnecessary for the driver anyway.

That essential mechanical fuel gauge has very few components, and its operation is similar to that of a voltmeter (analogue meter measuring voltage).

The first part of this system is the sending unit. The sending unit is located in the car’s fuel tank. It consists of a float, usually made of foam, attached with a thin, metal rod. The rod end is mounted on the variable resistor‌. A resistor is an electrical device that stops the flow of electricity. High resistance, low current. In the fuel tank, one side of the variable resistor consists of a strip of resistive material connected to ground. The wiper connected to the gauge slide along this strip of material conducts power from the gauge to the resistor.

Photo: VW Parts Vortex

If it is close to the grounded side of the wiper strip (represented by the circuit in the figure), the resistance of the current is low, so the resistance is small (and the current is high). If the wiper is at the other end of the strip, there will be more insulating material in the path of the current, so the resistance is more considerable (and the current is lower).

The second part of this system is the fuel gauge, which is the current meter. The lower the fuel level, the higher the resistance and the higher the level, the lower the resistance. The current from the resistor goes to the gauge, which response to the amount of current flowing. At high resistance, the current is low, and at the gas gauge, the needle is low. At low resistance (full tank), the current is high, and the needle is reflected at the fuel gauge. The fuel gauge works this way.

Due to their simplicity and reliability, fuel measurement and its performance have not changed much in decades. However, like almost everything in a modern motor car, some electronic equipment is included to complete it rather than a proven scientific fit.