Is It Harmful to Rev the Engine in Neutral Gear?
3 Answers
Revving the engine in neutral gear is harmful. Impact on engine reliability and lifespan: When the car is in neutral gear, the engine has no power output. At this time, revving the throttle causes the engine speed to rise sharply. Moving parts such as pistons and connecting rods undergo rapid acceleration, generating significant acceleration forces and subjecting them to substantial alternating loads. The forces on pistons, piston pins, connecting rods, connecting rod bolts, and crankshafts will exceed those during normal operation, affecting the engine's reliability and lifespan. Cylinder scuffing and bearing seizure failures: Due to the sharp increase in engine speed when revving, lubrication at various friction pairs cannot keep up, making it highly prone to cylinder scuffing, bearing seizure, and other failures.
I often see people revving the engine in neutral at red lights—this is a really bad habit. Lightly tapping the throttle briefly isn’t a big issue, but sustained high RPMs are like making the engine drink cold water on an empty stomach—the oil pump pressure can’t keep up, leading to insufficient cylinder wall lubrication and accelerated wear on the crankshaft bearings. Look at seasoned car modders; they’ll blip the throttle a couple of times in neutral just to hear the sound and then stop, because they know prolonged high temperatures can prematurely kill the catalytic converter. Last time I helped a neighbor diagnose his car, blue smoke from the exhaust was a result of burning valve stem seals from revving in neutral. Modern cars with start-stop systems are even more delicate—revving in neutral might trigger system errors. If you want to hear the engine’s tone, a light two-second tap in Park when the engine’s warm is enough.
During the last maintenance, the technician told me my throttle body was severely carbon-fouled, which reminded me that I often rev the engine in neutral. When the engine idles, gasoline burns incompletely, leaving residues that coat the throttle blades like tea stains clogging a teapot spout. Don’t be fooled by the instant fuel consumption gauge showing low readings—tests show revving to 3000 rpm for five minutes in neutral can burn half a liter of fuel, while idling with AC uses only 0.8 liters per hour. The transmission also suffers, as the oil pump can’t circulate fluid to the load side, causing the valve body temperature to rise. The fuel injection system takes the biggest hit—the ECU thinks it needs to climb a hill and dumps extra fuel, confusing the oxygen sensor. Now, I’d rather roll down the windows in traffic than rev the engine pointlessly.
