What is the purpose of a car tachometer?

[McHarley]

The main functions of a car tachometer include observing whether the car is started, determining the optimal shifting moment, indicating the safe operating range of the engine, and detecting potential vehicle malfunctions. Engine speed reflects the working condition of the engine and is one of its most important parameters. The unit symbol for the car tachometer is r/min, and the unit name is revolutions per minute. The scale range of the tachometer reflects the engine's speed range, where the white-marked section indicates the safe speed range, and the red-marked section indicates the dangerous speed range. Below is a detailed explanation: Observing whether the car is started. One use of the tachometer is to observe whether the car is started. When the car is not running, it will be in an idle state. At this time, the tachometer needle does not point to 0 but to a position above 700 rpm. Therefore, at any time, if you are unsure whether the vehicle is started, you only need to check the tachometer. Determining the optimal shifting moment. For example, when you want stronger power or when driving uphill or downhill, it is advisable to shift gears after appropriately increasing the engine speed. Alternatively, if you are pursuing fuel economy, ensure the car shifts at the lowest possible speed under smooth conditions. Even for automatic transmission models, manual mode can be used when pursuing power demands. In the past, many people relied on engine sound to shift gears, but as vehicle soundproofing improves, engine noise is hardly audible anymore. The most accurate method is to determine the shifting moment based on the engine speed. Detecting car malfunctions through the tachometer. For instance, using a stall test to check internal wear in an automatic transmission; if the engine speed is high while the vehicle speed is low, and fuel consumption increases significantly, it may indicate that the torque converter lock-up clutch is not engaging or the lock-up speed is too high. Performing an acceleration test in place can check the engine's working condition or whether the clutch in a manual transmission model is slipping. These are common diagnostic methods used by car mechanics. Indicating the engine's safe operating range. The tachometer usually has a red zone, typically above 6000 rpm. For the engine, maintaining excessively high speeds for prolonged periods can lead to poor lubrication performance and increased strain on the cooling system. Prolonged operation in the red zone can cause varying degrees of damage to engine components. Therefore, the engine's condition can be assessed based on the safe range indicated by the tachometer.