Possible intermittent alternator problem

Driving home in the hot, hot weather the other day, I discovered that the voltage meter was showing below the line between the 13 and the 8 and that the car wasn't running as well as it normally does. I turned off the lights and fan and I was able to get home, but the gauge never improved. If anything, it continued to get closer and closer to 8. I let it sit overnight and the next morning when I started it up, everything was fine with the voltage again, the motor ran strong, and I couldn't replicate the problem after a short drive.

The first time that the voltage dropped while driving happened only a couple of weeks ago during another long drive while I was stopped at a light. I was able to get the voltage to go back up to normal after I revved the engine, but this time it didn't work.

The battery light works properly when I turn the key and then it goes off after I start the car. I have what appears to be the original Motorola alternator w/ 50,000+ miles on my car. So it appears that after driving around for an hour or so, the problem occurs and fixes itself once it sits for a while. Of all the alternator failures that I've had on my other cars, once the alternator died, it died and didn't work intermittently, so this one has me scratching my head. Does this sound like the alternator is in need of replacement, or is there something else that I may be overlooking? I haven't had the alternator tested.

You could have an internal problem with the alternator. Before taking the alternator off check the belt tension and see if there is any sticky black goo dripping out of it from the bottom.
David Teitelbaum

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Originally Posted by David T

You could have an internal problem with the alternator. Before taking the alternator off check the belt tension and see if there is any sticky black goo dripping out of it from the bottom.
David Teitelbaum

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The belt is not as tight as the AC compressor belt, but it turns the alternator well, from what I can see. Does it need to be tighter?

No sticky black goo dripping from the bottom. Clean as a 30+ year old alternator can be.

What do you recommend next?

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Originally Posted by Stainless

The belt is not as tight as the AC compressor belt, but it turns the alternator well, from what I can see. Does it need to be tighter?

No sticky black goo dripping from the bottom. Clean as a 30+ year old alternator can be.

What do you recommend next?

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With the motor OFF, grab the fan on the alternator and try to turn the pulley. If you can, it is probably too loose. If you can't, then many places will check your battery and alternator for free.
David Teitelbaum

I just went through a simmilar circumstance with my DMCH alternator which was just over a year old. On a hot day driving with the AC on and my cell phone plugged into the cigarette lighter my battery light started flickering and the voltage guage started swinging wildly donw then back to normal then down. I turned everything off and it seemed better. I made it home OK. I checked with a volt meter at the battery and it showed 11.5 volts.

The next day I started the car with no problem but still the volt meter at the dash said just over 8. Meter again read around 11.

I thought it might be the belt slipping so I bought a replcaement. Auto Zone didn't have the right length so I bought 1/2 inch shorter. The thickness syas it's the same but it "feels" narrower. Any way I replaced it but there was no effect.

Long story short, I got a new alternator from DMCNW and replaced the old one. Decided to keep the new belt just for giggles. First day everything seemed fine - voltage on the dash sits just over 13 but occasionally would go higher... A little concerning but... With AC on etc, I get a drop in voltage at idle.

Today it sits in around 13-14 and drops considerable at idle with AC on, etc. Meter still says about 14.5 but occasionally dips down expecially when the AC compressor kicks on.

My question - What does a "normal" function look like? Doe the voltage stay constant even when AC compressor kicks in? What about the fans kicking on when the engine's just hot. My truck - a 90s Dodge is solid as a rock no matter what's going on. Is this just what old cars do?

Cheers
Steven

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Originally Posted by mluder

My question - What does a "normal" function look like? Doe the voltage stay constant even when AC compressor kicks in? What about the fans kicking on when the engine's just hot. My truck - a 90s Dodge is solid as a rock no matter what's going on. Is this just what old cars do?
Cheers
Steven

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take your bycicle and drive it on a flat or downhill, and then ride it uphill. Do you always get the same speed ?
Well, I don't, I feel that whend riding uphill I need to work more and get slower.

Ok compared to an alternator this means - more current - more work !
The belt has to carry more load, and all the electrical connections get a higher voltage drop because
the resistance is contant and muliplied with the current - you get the voltage drop/loss.

this means - fix your electrical connections from the alternator up to where they go to the interior at the fire wall.
also on the inside!
+12V AND GROUND !

I found on my car that the Ground connection to the frame below the water bottle is where I get the greatest losses
and have to fix this every few years.

Your newer car just doesn't show you small differences and voltage drops because they don't want people to come
to the shops asking stupid questions and generating useless work for them. I bet these are not even real volt meters,
instead those are just gauges telling people - well, everything is green and fine.
And I expect in a new car that the voltage drops are improved or still better because there's no oxydation yet.



Motorola alternator - worn brushes or the regulator is ready to be replaced.
Test it at night - everything off - the bulb alternator bulbs is as dark as it has to be when the enigne is running.
If you can see it slightly glowing when the motor is runing - brushes are worn.