Geo Metro Alternator

I have a '92 Geo Metro that keeps on killing the alternator. I’ll bring the failed one back to the parts store, get a free “lifetime warranty” replacement and, maybe a month or so later, my battery’s so dead, it won’t start the car. I jump start it and it starts running, but if I then remove the positive battery lead, the car stops dead. I bring the alternator and battery to the auto parts place and they tell me that the battery’s good, but the alternator is bad. I then repeat the cycle.

I’m trying to figure out what could be causing the alternator to fail. Anyone have any suggestions about how to troubleshoot this?

What is the mode of failure on the alternator? What exactly about the alternator is failing? Fried regulator portion (blown diode)? Failed bearings?

First off, stop disconnecting the positive cable from the battery while the car is running.
That can, and does, damage the cars electrics, including the alternator.

Next, you might want to think about replacing some parts on that car to help eliminate possible issues.

Replace both battery cables (pos and neg).
Replace the engine ground strap/cable.
Get a new battery the next time you get a new alternator. Weak batteries cause the alternator to work harder, causing them to have a shortened lifespan.

And test the charging system while it’s on the car, and operating.


I’ll replace the cables.

The last time the alternator died (about 2-3 weeks ago), I took both it and the battery to the parts place. They put both on the good/bad machine and told me “battery good”, “alternator bad”.

Is there a straightforward way to test the charging system?

Before replacing things I suggest you first try to locate the trouble, unless the cables are in bad shape already.

There may be a problem with the wiring to the alternator. Perhaps the exciter lead is grounded and causing the alternator to put out full output. If the alternator stays real hot then that may be the trouble. Check the voltage drop across the battery leads and between the alternator output and the positive battery post while running. There should be very little voltage across the connections.

Take the car to an automotive electrician; or, to a mechanic who has an understanding of electrical circuits. There is an electrical short which is putting excessive load on the alternator. Ask around for recommendations.

This car probably has a fusible link in which the alt. current passes into the battery. Since this is a high current deal, meaning a lot of heat, it’s possible the fusible link ends could be burnt or corroded.

This could even be an intermittent thing and during the spells when the contact is bad the battery voltage will drop. This means the alternator will sense the lowered voltage and start putting out its maximum. Since the current can’t pass into the battery the alternator will fry itself.
Just a suggestion anyway.

I had an alternator fail on a '94 Metro and bought a rebuilt alternator that only lasted a week, the free replacement was dead in the box. I asked if I could just get my money back and bought an OEM alternator from the dealer and that one is still working. Yes, OEM alternators are pricey but life is too short to change one alternator after another on this particular car which has one of the most inaccesable alternators in the world.

I have to agree with the quality of OEM parts vs. some remanufacturers. Some companies only replace the part(s) that caused the alternator, starter, etc. to fail. They may inspect/replace some basics like bearings, but you’re often still getting a mostly-used part with a lot of miles on it. IMHO, OEM (or at this point at least a different rebuilder) is the way to go for you.