Push start

The Honker II, which is a midget racing car getting a push start by a Toyota Landcruiser at the 144th Wagga Wagga Show.

Attempting to push start a motorcycle.

Push starting, also known as bump starting, pop starting or crash starting is a method of starting a motor vehicle with an internal combustion engine by engaging the manual transmission through the motion of the vehicle. The technique is most commonly employed when other starting methods (automobile self starter, kick start, etc) are unavailable.

The most common way to push start a car is to put the transmission in second gear or reverse, switching the ignition on, applying the clutch, and pushing the car until it is at a speed of around 5 to 10 mph (8 to 16 km/h). This can be done by one person on a motorcycle, or with a car or truck if they are strong enough and/or the car is light enough and/or the vehicle is facing down a hill; a heavier vehicle requires help if not on a hill. When at speed, the clutch is quickly released. By pushing the car, the wheels make the gearbox rotate, and by engaging the gear with the clutch, contact is made between the wheels and the engine, which may make the engine start by the power of the turning wheels (as the engine's starter would normally do). As soon as the engine can be felt and heard starting, it is advisable to again press in the clutch to prevent the engine stalling, or the vehicle jerking out of control. A too slow rolling speed may result in the engine not being able to start.

If the vehicle's battery is severely discharged, the push starting technique can be unsuccessful, as the battery may not be able to provide sufficient voltage for the ignition system to function (or in the case of a diesel engine, to preheat the glow plugs, although this will not generally prevent starting altogether but just make it much more difficult). Also vehicles with an electronic engine management system will not start if the battery does not provide sufficient voltage to operate it. In such cases, recharging the battery or attempting a jump start is a better option.

Push starting a car is typically only possible in manual transmission vehicles, as automatic transmissions usually depend on pressure generated from a pump driven off the input side of the transmission to operate the gear selection mechanism. With the engine not running, this pump is inoperative, so the transmission remains in neutral and cannot transmit drive to the engine. Even if this was not the case the poor performance of the torque converter at transmitting torque in the reverse direction would require the vehicle to be moving at an unreasonably high speed for the technique to work. Most vehicles with automatic transmissions cannot be started this way because the hydraulic torque converter in the transmission will not allow the engine to be driven by the wheels (some very old automatic transmissions, e.g., General Motors' two-speed Powerglide transmission, have an extra pump on the output shaft which can power the transmission's hydraulics, and cars equipped with such transmissions can be push started).

In the early 20th Century, many motorcycles could only be push started; the 1908 Scott was distinguished by introducing a kick starter feature. Excelsior Motor Company's Welbike, intended to be carried by paratroopers in World War II, was designed to be started only by push starting.

See also

• Starter motor
• Ignition system
• Jump start