What are the hazards of starting a car while it's already running?

[Winifred]

Starting a car while it's already running can cause several hazards, as detailed below: Damage to gears: If the engine is started again while already running, the most vulnerable components are the gears, specifically the engine's flywheel and the starter motor's gears, which can suffer damage from meshing improperly. Damage to the motor's copper sleeve: The reactive force from the engine can impact the starter motor, potentially harming the copper sleeve. While occasional instances may not cause significant harm, repeated attempts can lead to engine damage. No impact: Some modern vehicles are equipped with start protection mechanisms. When the engine is already running, turning the ignition key to the start position either prevents the starter motor from engaging or makes the key immovable. Certain vehicles, however, allow the starter motor to operate even when the engine is running, thanks to optimized system designs that ensure no adverse effects occur even if the starter motor is activated.