What is the normal RPM for an automatic transmission car?
2 Answers
For automatic transmission cars, an RPM of around 1800 to 2000 is normal, but the required speed varies depending on different road conditions. The engine RPM should match the current gear; otherwise, driving at high speed in a low gear or at low speed in a high gear can cause unnecessary damage to the vehicle. The engine RPM relates to the number of work cycles per unit time or the effective power output of the engine, meaning the effective power of the engine changes with different RPMs. Therefore, when specifying the effective power of an engine, the corresponding RPM must also be indicated. During a cold start, the idle speed of a car is mostly between 1200-1500 rpm. This is because when the car starts, the engine temperature is low, and the higher speed helps quickly raise the engine temperature. An automatic transmission car can shift gears freely when the RPM reaches around 1800 to 2000 rpm. The gear shifting in an automatic transmission car is determined by the computer (or chipset) based on the current speed, RPM, and throttle input.
As someone who drives to work regularly, I believe the normal RPM for an automatic transmission car should be between 600 and 800 when idling. Once you start driving, such as in stop-and-go city traffic, the RPM may fluctuate around 1500 to 2500. On the highway, during cruising, it might stay around 2000 RPM. However, when accelerating or climbing hills, it could surge above 3500 RPM, which is all normal. I've noticed that engine type affects RPM: gasoline engines tend to run slightly higher RPMs than diesel ones, and newer cars with electronic controls make it smoother. If the RPM is abnormal—like dropping below 500 at idle or spiking above 1000—it could indicate a dirty idle valve or transmission issues, requiring immediate inspection. Keeping an eye on the tachometer is a good habit, helping detect problems early and extending the car's lifespan.
