How early can you know about a bad alternator?

had the 94 station wagon checked before an 8 hour road trip. nevertheless, on the way home, i got stranded–pregnant and with 2 kids alone at night on I66 in the middle of nowhere and 2 hours from home. dead alternator. warning light blinked for maybe one minute before everything – lights, dash, even the emergency blinkers (almost) – died. so i’d like to know if i can be a bit irritated with the shop that checked over my car - did they miss something? or does an alternator just quickly die like this? thanks!

Yes, an alternator can quickly and unexpectedly die.

An alternator can also fail in ways that can be detectable while the engine is still drivable. Apparently yours failed in a way that was sudden and unexpected. Sometimes stuff just happens.

Last alternator I had to replace was on my 84 S-15. That and every alternator I replaced before that just died…no warning…one day it’s working…the next day it’s not.

You can certainly be a “bit irritated” with the shop that checked over your car if you are looking to displace your anger. However, chances are, no shop would have done a load test on your alternator, which is about all that can be checked, to see if it was producing the exact output it is rated for. This would tell you if one or two of the three diodes that are likely in your alternator have failed prior to you leaving on your road trip. But again, that isn’t standard practice, and most mechanics will simply look to see that the alternator is in fact working, and call it good. So in reality, the shop checked your car for any visual indication of pending failures, including pending engine codes, and gave your car a clean bill of health because it was in fine shape when they checked it out. You were driving at night with your headlights on which put a strain on a (possibly) almost-wore-out alternator, which pushed it over the edge. An alternator can just go out all of a sudden with no warning, so when you’re finished being irritated, lighten up on the shop and move on. That is one of the joys of driving a used car (probably with over 100K miles). Stuff happens.

A couple of things,alternators never put out exactly what they are rated 80% is OK,a load test for max alternator output is not very good at detecting open or shorted diodes,you need to scope the alternators output and look at how much AC is mixed up with the DC and what shape the AC waveform is.

Your car should have ran a long time after the alternator stopped output.

What I think was missed here (and you could bring this to the shops attention) is the batterys health was not checked by both a conductance test and a typical load test with a carbon pile.

Sounds like you were driving on a crummy battery that couldn’t not carry the cars load for any amount of time.

Agreed that an alternator can go belly-up in a nano-second, which is often the case.

The car is a '94 and if the alternator is the original it’s had a good life up to that point.
It is impossible for even the best shop or techs to determine how much life is left in many parts on a car. The alternator is just one of those parts.

And I assume the alternator has been diagnosed and replaced at this point and the problem is not something else that may lead one to believe the alternator is at fault. (battery cable, junction terminal, fusible link, ignition switch, etc.)

How can you blame the mechanic for the alternator going out, or you getting pregnant?

There definitely are some facts left out that might shed some light upon this.

Absent of details, a pre-flight check of a car for a trip usually is limited to visual inspection under hood, checking all belts and hoses for cracks, checking coolant, makign sure battery does not have a pile of corrosion on the terminals, or rotted out cable-ends, fluid levels checked, make sure you got a full tank of gas.

Really, unless you know the folks from Pimp My Ride, that is pretty much all one would sensibly check.

It sounds like that 4500.00 is calling for you !

Time for a new car, one with ON-STAR, perhaps.

The main cause of alternator failure is an old battery that can’t supply ample current for the cars accessories. Start up current on many devices exceed the alternators capabilities so it reliant on the battery to supplement the load.
If the battery had been replaced every 4 years (based on 15000 mi/year), the alternator would still be humming along.

Yep, in the old days when you could overhaul your own alternator for about $20 and 1/2 hour, I would do it about every 70,000 miles as a precaution. New bearings, brushes, and voltage regulator. In about a million miles I have never had a diode fail. I’ve had plenty of internal voltage regulators fail and a few bearings but never a diode as much as people talk about them.

I agree though, the battery should have been good for at least 50 to 100 miles after an alternator failure and if you had a good battery, you should not have gotten stranded. On an overnight 200 mile trip, having to use lights, I even stopped and got the battery recharged in order to make it home. Batteries should be replaced every 3-4 years in my view and you shouldn’t have gotten stalled.