On Tue, 1 Mar 2005, Smitty wrote:

> I took my 96 grand Cherokee in for a water pump replacement. The shop
> said that I also had a bad alternator. It worked fine in our -20 temps
> here in MN and the warning light has never come on. Do you think it
> could be bad?

Let me share a story which will help illuminate the matter:

At one time, I drove a very used 1991 ex-police Chev Caprice. One very
cold winter morning, I noticed a new noise from under the hood. Faint, but
present. Sort of an intermittent hissing/clicking sound coming from the
front. I carefully homed in on the alternator as the source of the noise
and made a mental note to replace it, for obviously one or both of its
bearings had begun to fail.

But life being what it is, I didn't get around to it. Working on cars is
very little fun in the winter, and the alternator was continuing to
charge. I fed a few drops of oil into the front bearing via the shaft and
kept on driving, periodically reminding myself that I ought to look at
changing the alternator. Eventually I pretty much forgot about it.

About 2 months later, I was on the highway doing about 65mph when a sudden
loud noise began to emanate from up front. It sounded like the moan of a
dead power steering pump, but it obviously wasn't, for I still had
steering boost. The noise rapidly grew louder and evolved into a
hair-raising grinding noise. The voltmeter dropped, the "AMP" light came
on, and the smell of very hot metal filled the car. The alternator's front
bearing had locked up solid, and the entire bearing was now spinning in
its interference fit, meant to keep the bearing's outer ring stationary in
the alternator's front housing.

It was still about 3 miles to the next exit. I decided to go for broke,
and kept on driving. The grinding sound got ever louder, the stink of
broiling metal grew heavier and hotter. I pulled off the highway at the
first opportunity, and found...nothing. No service station, no phone
booth, just an intersection.

Back on the highway, another mile down the road, I pulled off at the next
exit, into a gas station's parking area and killed the engine. I yanked
the hood release, lifted the hood, and a thick column of smoke poured up
from the *extremely* hot alternator. The once-greasy painted brackets were
now bare steel, dark pink in color. I ran into the convenience store,
bought a bottle of water, sprinted back outside and carefully poured it
over the alternator. The water instantly and loudly flashed into steam. I
bought another bottle of water, and another. By the time I had poured the
third litre of water over the alternator, it was merely fizzing rather
than flashing the water directly into steam.

There was a parts store with a service department one block down the road,
so I got back in the car and started the engine. The water treatment had
averted fire danger due to extreme heat, but in the time it had taken me
to buy the first bottle of water, the alternator had welded itself solid.
The 3-month-old serpentine belt skidded over the locked-up alternator
pulley and cooked itself to death in a big cloud of noxious smoke
during the one-block drive to the service center.

Three hours and $250 later, the car had a replacement alternator and a new
belt, both of unknown quality.

If this is your idea of a fun diversion during an important trip on an
unpredictable day, by all means ignore your mechanic.

If it isn't, ask him to be more specific about what's gone bad in the
alternator. I'm betting he gave the alternator a spin when he removed the
belt to replace the water pump, and felt a rough bearing.

DS