When I start the car up cold I get the usual 14.4 reading on the dash, and a normal reading when I check the alternator of around 14.5, checking the battery I get between 14.4 and 14,5 with the engine running at an idle..This I consider normal...
But, when the car gets up to running temperature and I'm at idle, I get an erratic fluctuating reading that jumps from 14.1 to 14.4 at the alternator, a fluctuating jumping reading of 13.8 to 14.2 at the battery , and a fluctuating jumping reading of 13.4 to 13.9 on the dash..All the readings are at idle without the air on...The problem is the numbers jump around and don't stay at a steady reading for more then a second or two..When I take off and the rpms rise the reading on the dash gets steady again at around 14.0 to 14.1, which is again " Normal" ..All the jumping goes on at idle....Is this an indication that my alternator getting ready to die, or is this normal..??....WW

 

Mine has fluctuated between 12.9-14.3 after its warmed up for 6 years and I consider it normal.

 

Mine jumps all around as well, even as low as 11.6v with a/c on. It's been like this since new and mine is a 2005 model. Also, I've replaced the battery only once in 11 years. So it's normal for me.

 

Yes it is normal for OEM alternator. During startup the eng is running a little higher rpms than it does at operating temp. OEM alts do not charge at hot idle. But they do charge at warm up idle. You want to look for low V when driving.

I replaced my alt with a Billit Tech 170A unit that can charge at hot idle.

 

im looking to purchase one of these.

 

Normal, not to worry unless you want an expensive billet alternator

 

They work great. My OEM unit went bad so I upgraded.

 

Mine does the same thing, normal I guess.

 

You are talking about a couple of tenths of a volt...that's not significant. Before we had digital readouts, you never would have even seen that variation on a dash gauge and it would never have been a worry...drive the car and enjoy......................

 

Dipping that low(11v) is not normal. Fluctuation into the upper 12v range is normal. When the brushes go bad on the factory alternator the voltage starts to dip to 11v erratically. This sometimes comes with "flickering" dash lights that goes away immediately when you step on the gas. Specifically when the vehicle is warm. GM now makes a 160amp alternator for the C6. I got mine at Corvettemods.com. The website says 150amp but it come with a 160amp sticker when you get the actual part.

P.S. Another symptom if you know you have this problem is the volt gauge on the dash actually moves up and down erratically very quickly. It's very noticeable. If you see the gauge smoothly and slowly dip down to 12.5V at hot idle and stay there until you increase the RPM's then you do not have the above issue I am talking about. Granted mine started out this way which I assume was normal, then one day I realized the car was dipping all the way to 11.0v and bouncing around between 11.0 and 12.5 volts at idle.

 

You're within +/- 10% normally, wouldn't stress too much.

 

My gauge never went below 13.4 at any time, but the numbers jumping around very quickly was what had my wondering if I had a problem..Thanks for all the responses .......WW

 

I would check all of the connections for cleanliness, tightness, and no breaks -usually at the connector ends.

Obviously alternator output is a function of engine rpm's, not necessarily maximum available amperage. If you want more low rpm amperage, reduce the size of the alternator pulley. The dangers in doing this is over spinning the alternator at high engine rpms. Alternators are also a drag on available horsepower.

 

This is not normal. That's exactly how mine started. Jumped around a bit from 14-13 volts. I didn't think it was normal but the forums seemed to support its "normal" for our cars. Well over time it got worse and the voltages started dipping deep into the 11v range and I noticed my lights in the dash flicker at hot idle only. When it was hot out during the day it was the worst and the volts struggled to stay above 11.5 at idle.

Well I am here to say this is NOT normal. The following video also shows the same scenario but his didn't jump around a lot. But it proves that this is not normal. I have also changed my alternator to the new OEM GM 160 Amp replacement from Corvettemods.com

 

sounds okay to me