Does Shifting to Neutral at a Red Light Harm an Automatic Transmission Car?
2 Answers
Shifting to neutral (N) at a red light does not harm an automatic transmission car. The N gear disconnects the power transmission between the engine and the transmission, while the handbrake is used to prevent rolling and potential collisions. If the red light duration is short, using N gear along with the foot brake is acceptable. However, for longer waits, it is advisable to engage the handbrake. Using D gear and the foot brake while waiting at a red light is not recommended, as the D gear maintains continuous power output, which can cause the transmission to heat up and increase wear. Similarly, using P gear to wait at traffic lights is also undesirable, as engaging P gear locks the transmission gears. In the event of a rear-end collision, this could directly damage the transmission. The transmission is a mechanism designed to alter the speed and torque from the engine, and it can fix or change the gear ratio between the output and input shafts.
Last time I drove my dad's old Accord and stopped at a red light, I habitually shifted to N gear, and he lectured me all the way. The mechanic actually explained this: there's really no need to shift to N gear for short stops at red lights. When an automatic transmission is in N gear, the hydraulic oil pump does keep working to lubricate, but frequent gear shifts actually accelerate wear on the shift mechanism. What's most damaging to the car is staying in D gear and pressing the brake for long periods, as the torque converter remains strained, causing the transmission oil temperature to soar to 110°C. I later timed it specifically—for red lights under 30 seconds, just pressing the brake is fine. For red lights over a minute or in traffic jams, shifting to N gear + handbrake gives the transmission a breather, and I measured a fuel consumption drop of 0.2L.
