Why Can Pushing a Car Start the Engine?
2 Answers
Pushing a car can start the engine because the starter gear remains engaged with the flywheel after the engine stalls. When the car is pushed, the thrust force causes them to separate, allowing the engine to start. Conditions under which pushing can start the engine: When the battery is too weak for the starter to crank the engine, pushing the car can help. This works because the car is pushed while in gear, using the chassis to rotate the engine externally and initiate ignition. However, if the issue is not a weak battery or a faulty starter—such as an engine malfunction—pushing the car won't help, and the engine still won't start. Precautions when pushing a car: Generally, you should engage third gear in advance, hold the clutch lever, push the car to a certain speed, and then release the clutch lever to start the engine. Avoid shifting gears after gaining speed, as this can easily cause gear grinding and damage.
Push-starting a car works primarily because the mechanical force generated during manual pushing replaces the function of the electric starter. When the vehicle is pushed, the drivetrain rotates the engine's crankshaft. If the engine still has compression pressure and fuel supply, the ignition system can operate normally to ignite the air-fuel mixture, thereby starting the engine. This method is often used as an emergency solution when the battery is dead or the starter fails, but it only works with manual transmission vehicles. During the operation, several people push the car to a certain speed, the driver inside presses the clutch, shifts into second or third gear, and then quickly releases the clutch to let the wheels drive the engine rotation. The entire process converts gravitational potential energy into kinetic energy, saving time and money while avoiding the hassle of finding jump-start equipment. However, safety precautions are necessary—ensure the operation is performed on a flat surface to prevent accidents. This method is not applicable to automatic transmission cars due to their different design. As a car enthusiast, I've tried this a few times in older cars and found it as cool as reliving the classic car era.
