Gauges & Instrumentation

Car Gauges

How Various Gauges and Instrumentation Work

Gauges and instrumentation fitted on any vehicle's dashboard make essential components for making different measurements. The gauge is specifically used for displaying dimensional information using a pointer or a needle that moves along a calibrated scale. It measures the physical quantity of an item, e.g., the gap in space, pressure of flow and diameter of materials, among other parameters. Various tools are used to make these measurements, which can be simple and complex machinery. Gauges are classified into four main categories- the analogue instrument meter (with analogue display), digital instrument meter (with analogue display), analogue instrument meter (digital display) and the digital instrument meter (with digital display). Analogue and digital meters with an analogue display are easy to read and interpret while the digital and the other two are a little complex. Digital and analogue instrument meters with digital displays are usually used in cockpit instrumentation. Vehicle instrumentation also measures different parameters of the car and is fitted in the dashboard or control panel.

Types of Gauges and Instrumentation


It is used to measure the rate of speed of the vehicle. Initially, the speedometer comprised a cable that rotated inside a flexible tube. On one side, the cable was connected to the speedometer, and the other end was connected to the speedometer gear transmission. This design is now dated as modern vehicles now use electronic sensors to determine the speed of the wheel and send signals to electronically driven speedometers. The size of the tires affects the accuracy of speedometers, i.e. if the tires have a larger diameter than the original size, the speedometer shows that the vehicle is going at a slower rate than it is. Improper speedometer gear transmission on older cars also affects the accuracy of the speedometer readings. Cars experience this problem when the replacement transmission is installed. Vehicles that use electronic speedometers allow technicians to make adjustments based on the size of the tires. Special equipment like the diagnostic scanner is used to perform those adjustments.


It measures how fast the engine runs in terms of revolutions per minute (RPM). The information comes in handy if you are using a car that has standard shift transmission and want to change to an optimum RPM for the best acceleration or the best fuel economy. It has single digit markings like 1, 2, 3 and others along with an indicator that shows RPM X1,000, which means the reading should be multiplied by 1,000 to get the actual RPM. So, if the needle points at 3, the engine is running at 3,000 RPM. The gauge also shows how fast you should race the car; higher RPMs show that the engine is working harder and the fuel mileage is also pretty high. Usually, the tachometer moves to the red zone, which can lead to engine damage. However, some engines have an engine computer that protects the engine from going to the red zone.

Fuel Gauge

The instrument shows the fuel consumption of the vehicle. When the tank is filled up, the gauge shows a full capacity for a long time and slowly drops until it reads three-quarter full after which it moves progressively faster to the last quarter of the tank. When the falls to below E, it means only 1 or 2 gallons are remaining, and the tank needs to be filled up. Car owners should not let the tank to drop below a quarter. Usually, the fuel pump is submerged in fuel in the tank to keep it cool. Lower fuel levels (less than a quarter) expose the pump, making it run hotter than normal. Running a vehicle with low fuel levels shortens the life of the pump and can lead to its failure especially if it starts to draw in sediments in the tank.


It is used in modern automobiles using electrical systems. Usually, fully-charged batteries show 12.5 volts if the engine is not running. When the engine begins to run, the charging system takes over, and the voltmeter indicates 14-14.5 volts. The pointer is supposed to remain in that position unless the vehicle requires a heavy electrical load, e.g., when using the heater, wipers, rear defogger are all running at the same time. Such uses can cause the voltage to drop below 12.5, which means the battery is using some of its current. You may also notice that the dash lights become dim and if the vehicle runs at this voltage for a long period, the battery runs down further and may cause the car to shut off. Vehicles continually running below 14 volts should be checked, and if the voltage exceeds 15 volts, then the voltage regulator has a problem. Be sure to check the system for overcharging as it can damage the electrical system.

Warning Lamp Gauge

It measures the pressure of the engine oil in pounds per square. Most vehicles are fitted with an oil lamp that signals when the oil pressure is extremely low. Thus, if it lights up when driving, you should stop the car and shut off the engine.





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