What are the hazards of revving in neutral gear?
2 Answers
Revving the engine in neutral gear can damage the transmission, affecting the input shaft bearings and synchronizer gears, and may also lead to incomplete fuel combustion and easy carbon buildup. When revving in neutral gear, although the gear is in neutral, the engine's power through the clutch keeps the transmission's input shaft in constant operation. In this situation, pressing the accelerator causes the input shaft, intermediate shaft, and the constant-mesh gears on them to change with the engine's RPM, while the output shaft and synchronizers for each gear remain stationary. Prolonged revving in neutral gear or coasting long distances in neutral can harm the transmission, potentially causing wear, burning, or noise issues with the input shaft bearings, synchronizer gears, and synchronizers. Extended periods of revving in neutral can result in incomplete fuel combustion. If these gases accumulate outside the cylinders and ignite, the vehicle may spontaneously combust. Frequently revving in neutral gear can easily lead to carbon buildup, which may severely clog the catalytic converter in extreme cases. These malfunctions can cause corresponding components to overheat, leading to wiring spontaneous combustion, with potentially severe consequences.
I've seen many people rev the engine in neutral while repairing or idling, but this is not a good practice. The main issue is that running the engine at high speeds without load subjects components like pistons and crankshafts to unnecessary wear, significantly reducing engine lifespan over time. It also wastes fuel, burning gas unnecessarily, which is bad for your wallet. More importantly, there's a safety risk—if your foot slips or the gear is accidentally engaged, the car could suddenly move, potentially causing harm to people or the vehicle. When working in the garage, I recommend only briefly testing at low speeds, such as checking ignition or unusual noises, and never exceeding a few thousand RPM. Prolonged high-revving in neutral can also lead to overheating or excessive emissions, which is unfriendly to the environment. In short, develop good habits—safe driving is the most important.
