Does Coasting in Neutral Save Fuel in a Manual Transmission?
2 Answers
Coasting in neutral with a manual transmission does not necessarily save fuel and may even increase fuel consumption. Many modern vehicles are equipped with electronically controlled fuel injection systems. When the car is shifted into neutral, the ECU defaults to idle mode, increasing fuel injection to maintain idle speed. The fuel injection control system inherently has fuel reduction or cutoff functions. Coasting in neutral negates these functions while increasing fuel injection. When in gear, if the driver releases the accelerator, the computer enters coasting mode where the engine stops injecting fuel for extended periods. In neutral coasting, the computer maintains idle mode with continuous fuel injection. This explains why neutral coasting sometimes consumes more fuel. Due to engine braking effects, coasting in gear covers shorter distances. If unable to coast sufficiently in gear and needing to reapply throttle, fuel consumption increases further. Neutral coasting in manual transmissions can cause: jerking sensations; reduced braking effectiveness; accelerated engine wear; and increased risk of transmission gear fractures.
I used to think about this issue when I drove a manual transmission. Coasting in neutral doesn't actually save fuel because modern cars have advanced electronic control systems. When you coast in gear, the engine automatically stops injecting fuel, which means zero fuel consumption. On the contrary, shifting to neutral requires fuel injection to maintain idle, wasting fuel unnecessarily. I've tested this multiple times, and coasting in neutral always consumes more fuel than coasting in gear. Moreover, in terms of safety, staying in gear provides engine braking, making downhill driving more stable and preventing loss of control. I recommend drivers develop the habit of coasting in gear—it's both fuel-efficient and safer. Cars are designed to be used this way.