Which of the following is a sign of a failing starter motor?

A grinding noise when starting is a clear indication of a failing starter motor. This sound typically occurs when the starter gear, commonly known as the pinion gear, is not engaging properly with the engine’s flywheel. It may happen if the teeth on the gears are worn down, misaligned, or if the solenoid is malfunctioning, causing the starter to spin without fully engaging the engine. This grinding noise not only signifies that the starter motor is struggling to operate efficiently, but it can also lead to further damage if not addressed, potentially causing more significant issues in the starting system.

In contrast, excessive smoke from the exhaust points to issues related to fuel combustion, such as bad rings or valves, and does not directly indicate a starter motor failure. A smooth driving experience is representative of a well-functioning engine and drivetrain, not related to the starter motor. Meanwhile, a quick engine start suggests that the starter motor is performing well, engaging correctly, and has adequate battery power. Therefore, the grinding noise is distinctly linked to the malfunction of the starter motor itself.