CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

1991 Saturn SL alternator failure

I have had my third alternator failure in a year on my 1991 Saturn SL. The failure occurs after the headlights, windshield wipers, and heater/air conditioning have been in use simultaneously. I suspect that something that uses a large amount of electricity is damaged and putting enough strain on the alternator to burn it out. I have friends that have the same car and their mechanics have rerouted the electrical supply for the fan. Any information would be appreciated.

Also, a mechanic friend told me that parking on grass leads to moisture damage to the alternator. I live in a rural area where paved parking is scarce. This seems like baloney to me, but maybe someone can confirm this.

I think you need to get your battery load tested. You may need a new one.

I have a new battery. The battery load is considerable. If there is any instance that the battery is not getting charged by the alternator, everything goes out…turn signals, odometer, you name it.

Is this battery newer than your most recent alternator? The battery should makeup for excess loads that the alternator can’t supply, at least for the short term. I too have a Saturn SL, live in a rural area, but have no problems with the alternator. The grass theory is baloney.

That parking on grass story is new to me. I doubt that it is true. Cars in rainy New England or humid Floridah would have their alternators replaced every three months, if it were.

You could have a bad connection between your alternator and battery. If your alternator has an external regulator, that thing could also be the cause. A lot of modern alternator have them built in, though. One one assume the mechanic knows to check for that, though.

About the first possible, the alternator normally generates a voltage that exceeds the battery voltage so it can charge. As a function of the rotation of the alternator, that voltage varies with every rotation of the engine. Sure, it is DC but that voltage actually swings wildly. That’s called ‘ripple’. The battery acts as a filter so it averages out around 14.4 volt or so. The alternator actually needs to see this load for it to work properly.
If that filter (ie battery) isn’t always in circuit because of an intermittently bad connection, it actually ages diodes inside the alternator and - worst case - could do damage to other parts of the car because they are not designed to have more than 14-ish volt applied to it.

It is conjecture, of course, but that is why I think you may have an intermittently bad connection somewhere between your alternator and battery or battery and ground.

Just noticed this comment:
What’s the story with rerouting the fan, btw? They had the same problem as yours and rewiring the fan fixed it?

A rising tide lifts all boats and a good ground helps all electrical things. The one I like the most is the engine to body ground wire that usually stands alone. The one on my truck is near the master cylinder.

You would think that I’d clean it up some day if I think it is so important.

Alternators can fail for a number of reasons, rectifiers, regulator, windings, brushes, etc. Has anyone told you how the alternators failed? It would help to know. Are the alternators new from the dealer or are they re-manufactured? And do you keep replacing it with the same part from the same manufacturer. Unless the wire to the fan is prone to developing intermittent shorts I can’t understand how rerouting it would solve the problem. It might be worth a look though.

Yea, that’s why I was curious about the ‘rerouting’ as well. I
could see if they had some sort of issue with the fan motor, maybe having forgotten to put a proper snubber on, or maybe not putting a diode across the fan relay but rerouting wires does very little in this type of situation.

Most modern cars have a fusible link in between the alt. and battery. A lot of current goes through that link so it’s entirely possible for a link connector to burn or corrode.
An intermittent bulb connection on the red dashboard battery light can also cause an alternator to not charge.

More details about if the alternators are actually failing or not would help. It can be easy to misdiagnose something simple at times.
That line the mechanic gave you about wet grass is pure bunk.

I replaced the fusable link. They tell me that the alternators have failed. I think there is a failure in some other area that is creating a closed circuit and causing a drain on the battery and alternator. My guess is that it was the fan motor on the other car. I pulled the fuse for the fan motor on my car, but I won’t know if that solves anything until I get a new alternator in. I got the car in '07 for $300 and until this, I only had to put a couple of hundred bucks into it. It still gets great gas mileage and I can do most of the repairs myself. I’d hate to trash it.
Thanks for the tips. I’ll run down those suggestions.
I thought the grass parking advice was stupid, but I didn’t want to argue with the guy.

The next time you suspect an alternator failure try this. Turn the key to the RUN position(engine not running of course) and touch the alternator pulley with the tip of a screwdriver. You should feel a magnetic attraction by the alternator pulley if the alternator is good.

This is not 100% definitive regarding all alternator problems but it also doesn’t take much effort or time.
If the alt. is not charging and there’s a magnetic pull then I’d revert back to the alternator to battery circuit as having a flaw.