Is Lower RPM Always More Fuel-Efficient When Driving?
1 Answers
Driving at lower RPM does not necessarily mean better fuel efficiency. This issue cannot be concluded simply. Firstly, when coasting in gear with an electronic fuel injection engine, the fuel supply is automatically cut off (zero fuel consumption) when the RPM exceeds a preset value, which varies among different engines, typically between 1200~1500 RPM. Therefore, coasting in gear without pressing the accelerator consumes no fuel when RPM is above 1500, while it actually consumes more fuel when below 1500 RPM. More details are as follows: 1. For manual transmission vehicles driving normally on highways, national roads, provincial roads, or urban elevated roads without traffic congestion, most of the time the highest gear is used with RPM exceeding 1500. In this case, releasing the accelerator without pressing the clutch and coasting in gear results in no fuel injection (zero fuel consumption). However, if coasting in neutral, although the engine RPM is lower, the engine must maintain idle fuel consumption to prevent stalling. 2. However, due to the engine braking effect when coasting in gear, the vehicle speed decreases faster compared to coasting in neutral, resulting in a shorter coasting distance. Considering that after the speed drops, you need to accelerate again to reach the original speed, the actual fuel consumption difference between these two driving methods is minimal.
