Maybe someone has some deep insight into this. I thought I knew all
the answers, like "if your alternator goes bad then the alternator or
battery light will come on on the dash", but that's never been the
case. Our 16-year-old 92 SL1 had the alternator conk out last Friday,
and the only light that came on on the dash was "Shift to D2". At the
same time, funky noises were coming out of the radio and the engine
was pretty obviously having a hard time. Exact same symptoms as
previous alternator failure.

I know all those things are sensitive to voltage, and that "Shift to
D2" came on because maybe the transmission is more sensitive than the
others, but still: why doesn't the alternator or battery light come
on?

I think I remember hollering at somebody in this newsgroup, probably
15 years ago, saying that if the alternator fails then the alternator
light will come on. But in real life, it doesn't!

I spent Saturday morning taking the old alternator out and then, in
about one fifth the time, put the new one in. Geeze, you'd think that
after having done it before I'd remember how to orient the damn thing
to get it out more easily... but it had been like 8 years now, so I
struggled! The key is: take off the power steering pump. Loosen the PS
hoses from the clip on the bottom. Then move the PS pump all the way
to the firewall towards the center of the car. With it arranged like
that, it's a breeze. Next time, I'll remember! At a new alternator
every 8 years, that'll be 2016...

Tim.

Sounds like it may have been a diode failure. When a diode shorts an ac
voltage is added to the DC. Battery damps some of this but it is bad for
both the battery and any electronics.
Just out of curiosity, did you really wind out the engine before you found
the alternator was bad? The only wear items on an alternator are the brushes
for the field circuit and bearings. Sometimes the diodes go but when this
happens, more often than not, they short in pairs which effectively shorts
the output of the alternator. Belt starts screeching then.

"Tim Shoppa" <shoppa (AT) trailing-edge (DOT) com> wrote

On Apr 7, 5:40*pm, "Oppie" <bop... (AT) nospam (DOT) com> wrote:
I'm pretty sure all my alternator failures have been either single
diode or regulator failures. The alternator just quits charging the
battery. I hook up my meter, start the engine, and the voltage never
goes up like it should when being charged - just down. I can't tell
you that the alternator is really putting out zero current, just not
enough to charge the battery with all the accessories off and the
engine running.

My mother-in-law's early-90's Oldsmobile used a Delco alternator that
seemed nearly identical to the Saturn's, except that the mounting
brackets were at a different angle. When it failed, the alternator
light actually came on. Not sure if it was electrically different or
identical, but the connectors were identical to the Saturn's.

In my experience, the best quality rebuilt alternators seem to outlast
the original Delcos. The originals seem to last 4 or 5 years, and the
rebuilds maybe 10 years. (Actually we're driving the Saturn more than
in the past, so if you measure it mile-wise the rebuilt lasted 3 or 4
times as long as the original.) Maybe the best quality rebuilds have
better, more durable diodes/regulators/???

Tim.

"Tim Shoppa" <shoppa (AT) trailing-edge (DOT) com> wrote

On Apr 7, 5:40 pm, "Oppie" <bop... (AT) nospam (DOT) com> wrote:
I'm pretty sure all my alternator failures have been either single
diode or regulator failures. The alternator just quits charging the
battery. I hook up my meter, start the engine, and the voltage never
goes up like it should when being charged - just down. I can't tell
you that the alternator is really putting out zero current, just not
enough to charge the battery with all the accessories off and the
engine running.

My mother-in-law's early-90's Oldsmobile used a Delco alternator that
seemed nearly identical to the Saturn's, except that the mounting
brackets were at a different angle. When it failed, the alternator
light actually came on. Not sure if it was electrically different or
identical, but the connectors were identical to the Saturn's.

In my experience, the best quality rebuilt alternators seem to outlast
the original Delcos. The originals seem to last 4 or 5 years, and the
rebuilds maybe 10 years. (Actually we're driving the Saturn more than
in the past, so if you measure it mile-wise the rebuilt lasted 3 or 4
times as long as the original.) Maybe the best quality rebuilds have
better, more durable diodes/regulators/???

Tim.

I had a nippondenso alternator on a Chrysler minivan I used to own. Original
failed and I replaced it with same type. It failed within a year. Diodes
shorted to the point that I had to cut the drive belt to drive the car. Was
hard-wired so unplugging was not an option. Luckily this was not a
serpentine belt. Later found out that the 'denso alternators had a bad
reputation. I replace it with a Bosch that worked well till we junked the
car. The only problem with the Bosch was noise on the radio. Was going to
put in a suppressor but never got arround to it. I would guess that the
Bosch had different diodes that gave more noise. (High speed diodes have a
current spike when they switch from conducting to blocking)

You don't always get the idiot light when an alternator goes. That's
why I have a voltmeter gauge in my car.