This story was part of Counterman's annual Technical Sales Seminars, which was published in the April 2009 issue.
When a customer asks for a replacement alternator or starter, do you offer to bench test his old unit to make sure that’s really the problem? Or do you just look up the part number, ask him if he wants a new or remanufactured unit, and then finish the sale?
The latter sales approach is certainly faster and easier, but it often results in parts coming back because they failed to fix the customer’s problem. If the engine won’t crank, many people assume the starter is bad. Likewise, if the battery keeps running down, they assume the alternator is bad. Sometimes they’re right, but many times they are dead wrong.
Bench testing a customer’s old alternator or starter is always a good idea because (1) it will confirm whether or not the old unit is good or bad, and (2) if it tests good, it will prevent an unnecessary sale and return because something other than the starter or alternator is causing the customer’s problem.
Cranking problems can be caused by a low battery, loose or corroded battery cables, a broken or missing ground strap, a weak starter solenoid, a bad starter drive, a damaged flywheel (broken teeth), starter misalignment, loose, corroded or damaged wiring in the starter circuit, a faulty ignition switch, park-neutral safety switch, brake safety switch, the anti-theft immobilizer system, a mechanical problem inside the engine (such as a coolant leak causing hydrolock), or even the wrong oil viscosity (oil too thick for cold temperatures).
Charging problems can caused by a faulty voltage regulator (internal or external), a faulty PCM (if the PCM controls voltage regulation), loose or corroded battery cables, a loose or missing ground strap, loose, corroded or damaged wiring in the charging circuit, a blown fuse in the power distribution center, or a slipping drive belt.
Bench testing your customer’s starter or alternator won’t tell you which of the above may be causing his problem if his old unit tests good, but it will tell him he has a lot of other possibilities to check before he buys any parts.
Hooking up a starter or alternator to a bench tester is relatively simple. The machine has a chart or manual that tells you which adapters and settings to use, so as long as you follow the directions you shouldn’t have any problems. When testing a starter, the machine will measure the cranking speed of the starter and how much current it is drawing. If the starter is spinning too slowly or is pulling too many amps, it will read bad.
When bench testing an alternator, the machine will measure the alternator’s voltage and current output at a specified rpm. If the unit is not putting out enough amps or voltage, or there are voltage fluctuations or leaks due to bad diodes, it will also test bad.
VERIFY THE OPERATION
The bench tester can also be used to handle warranty returns and complaints. If a customer returns an alternator or starter claiming it didn’t work, you can verify the operation of the unit on the tester. Guess what? Most new and remanufactured alternators and starters that are returned by customers test good. The reason why is because the customer misdiagnosed his electrical problem. The problem is not a bad starter or alternator, but one of the other possibilities we already mentioned.
Starters are pretty rugged, and will often last the life of the vehicle today. Electronic fuel injection and low-drag 5W-20 and 5W-30 motor oils allow quick starting, so the starter barely gets a workout. But if the engine has another problem and requires prolonged cranking, it can overheat and burn out the starter.
Alternators, on the other hand, have to work much harder in late model vehicles. With so many electrical accessories and onboard electronics, current loads can be very high more than 100 amps in some cases.
This causes the alternator to run hot, which over time may cause it to fail. An alternator’s maximum output capacity should equal or exceed the maximum load created by the vehicle’s electrical system.
This includes the voltage needs of the ignition system, fuel system, lights, A/C, radio and other power accessories. Alternator output is proportional to speed, so to achieve maximum output the engine has to be running at 2,000 to 2,500 rpm or higher to keep up with high electrical loads. Sitting and idling for a long period of time (especially during hot weather) with the A/C, lights and radio on may overtax the alternator and cause it to overheat and fail.
Vehicles that are equipped with extra electrical accessories (like police cars or sport compact cars with 1,000-watt subwoofers) are especially hard on stock alternators. For these kind of applications, recommend upgrading to a high-output aftermarket alternator.
Replacement alternators (new or reman) should always have the same or higher amp rating as the original.