Did I install a bad alternator?
 

My niece has a 2001 Lexus IS 300 which has been having issues with the battery/alternator. I went to the car yesterday and it was DEAD. So I pulled the battery, took it to AutoZone, they charged it and said the battery is good. So I clean the battery post and the cable connectors, install the battery and fire it up. I have a www.ScanGauge.com (an OBD2 tool) so I plug that in and watch the volts.

When started the volts read 14.1. I take the car for a drive and the first stop or 2 the volts drop to 13.6 - 13.8, no big deal. About a mile away, 3 minutes into the drive, I stop at a light and the volts drop to 12.3 - 12.4. I drive a few miles and at stops the volts drop as low as 11.7. I figure the alternator is dropping off line and at low idles, I may just be reading battery voltage. It goes a little higher when I turn off the AC and head lights.

So I figure the alternator has an issue. I tell my brother and suggest a Toyota or Lexus part, he calls his son that works at a Lexus dealer, they call me back and tell me to go to a local auto parts store and get a new alternator for $125 with a lifetime warranty. I don't put up a fight and go forward and install the store box alternator.

I crank the car, 14.4 volts, I drive the car and a mile down the road I stop at a traffic light and the darn volts drop to 12.2 - 12.4. Another mile down the road and it drops to 11.9 volts. While driving it is between 13.8 - 14.2 volts.

Did I get a bad alternator from the store or does this car have another issue?

Tough call. I have been burned enough buying cheap parts from discount parts stores that I would definitely suspect the "new" alternator. A little spooky though that the symptom is the same with both alternators, but at the same time that is how an alternator with a bad voltage regulator acts.

Yea, I think I got a bad rebuild. I once changed one on a Mini and the darn thing caught fire in about 20 seconds. I will likely change it out.

If the voltage is dropping when you are stationery only, but with the engine running could that not be due to the battery being fully charged?
I note you said that whilst driving the voltage is between 13.8 - 14.2, about normal so it is not drawing excessive power when the car is operating and mobile.
If the battery was down a bit the voltage reading whilst stationery would of course be higher to top the battery back up wouldn't it?

My thoughts and experience is that the voltage regulator should keep with voltage steady throughout the operational range. When my car is idle the volts read between 13.4 - 13.6, while driving around 13.7. If it drops below 13.2 it is likely not charging at all. I could be wrong. :?

Ha, you got me curious. Which store did you go to?

AutoZone...

Yes, true but if the battery is fully charged, is not the regulator mean't to adjust the charge(voltage) to suit the load drawn off or necessary to maintain the battery at its correct full charge. Any more is really just cooking it.
Using my 'Ultragauge' on my V40 at idle my readings are 13.6 or a little more without accessories etc.
Whilst on the move it goes up to a range of 14.2 through to 14.6.
My installed battery is 7 years old now and still operating without any issues.

Ha ha!! I knew it. I have heard many times from many people that there line of alternators called tough-one or something, are absolute rubbish. They are all refurbished. Almost all the stories I have heard of are people putting them in and immediately having problems( like bad bearings or not charging correctly at all like in your case). Go and get your money back sir. I am in no way saying a refurbished alternator is bad, just that one sucks. I have heard far more bad then good about auto zones alternators. Sorry man.

I forgot to mention that I am in no way laughing at you, it is just that when I read your post and how you said you went to a local store and got one with a life-time warranty, I knew it had to have been that one. I know the lifetime warranty is tempting. If that is what you are really looking for, get an alternator from fcp. They take anything back for any reason, from you dont like the way it looks to 5 years later it fails.

LOL, I know it's not personal and I got a good laugh from your post as well. The crazy thing about this is that my niece's brother-in-law works at a Lexus dealer. I was shocked when he recommended they get a alternator from AutoZone.

In 95% of the cases, a "lifetime warranty" means they hope you get rid of the car before the part fails. ;)

I was told that my battery was bad about 14 months ago. Still driving with it around the country. It drained down real low when I was having charging issues in my 850.

Maybe that has something to do with your voltage readings?
Have you tried a different (good) battery in the vehicle and noted the voltage readings at idle or running as previously for any change. i.e. improvement
The new alternator may be struggling to handle the voltage loss from the old battery?
Just another theory Robert.

Wow, It just occurred to me what you said also. Why would he have recommended you to auto zone lol. Thought he would have thrown his own alternator in your face.

It is NOT my 850 with the problem. The issue is on a Lexus.