How to Spot Symptoms of a Bad Starterby Richard Rowe
A modern starter is composed of two primary parts: the primary motor that turns your crankshaft and starts your engine, and the solenoid that simultaneously engages the starter's drive gear and closes the main motor's hefty electrical contacts. Built for ruggedness and durability, starter motors and solenoids don't typically fail outright. Instead, most modes of starter failure will trigger a number of symptoms that range from somewhat-indicative to almost-definitive.
Attempt to start the car, and pay attention to the lights in your instrument panel and interior. Electric motors, supplied with a certain voltage, will always try to spin at a given speed. If the motor's internal wiring develops an internal short -- one wire connects to another inside -- the wiring will draw more amperage from the electrical system than it otherwise would. This will draw energy from the rest of the system, most noticeably, the lights.
Listen for a chugging sound while cranking. While a certain amount of chug is normal, particularly at low cranking speed, a chug accompanied by dimming and brightening lights may indicate a mechanical failure in the motor's bearings. If this is the case, you may be able to get by for a while by hitting your starter with a hammer from underneath in order to break the starter shaft loose. But, probably not.
Listen for the solenoid click. Starter solenoids typically let off a very noticeable click when they engage; this is the sound of the gear drive engaging and the electrical contact closing. If you hear a click, you can all but rule out the solenoid as a mode of failure. A series of rapid clicks indicates a solenoid rapidly engaging and disengaging. Most of the time, this indicates a lack of power from the battery, but it can indicate a problem with the solenoid.
Listen for grinding and freewheeling. A grinding noise indicates that the starter's drive gear isn't disengaging from the flywheel's gear teeth, or isn't engaging the flywheel completely. Along with or separate from grinding, you may hear a whirring after starting that sounds something like an electric motor or jet engine. The starter's drive gear has a freewheeler in it that keeps your engine from over-running the starter motor and driving it like a generator. The whirring you hear is the sound of the gear failing to disengage, which may indicate a bad return spring or solenoid.
Have your battery tested. There's no sense checking the voltage yourself; even a completely fried battery can exhibit near-normal voltage while not cranking, and you have no way of knowing exactly what the voltage drop should be while cranking. The simple route here is to remove the battery (if necessary) and have it tested at your local auto parts retailer. But, even if you have a bad battery, don't assume that's the sole cause. A starter with chronic high-amperage draw can drive the last nail into an old battery's coffin, and kill a new one. Simply replacing the battery may solve the problem for a while, but a bad starter will eventually kill the new one, too.