*VETTE*

2008 C6
One my second battery and second alternator.
Cold start voltage is 14.4v w/accessories 14.1v to 14.2v @ idle
After warming up I notice a voltage drop.
Fully warm @ idle my voltage will drop down to 11.9v almost killing my car and go up to 12.6v- 12.9v roughly.
So I instinctively thought alternator. Now I purchased a used but guaranteed working order through EBay. It seemed to do a little better than my original but still low.
When fully warm at idle with new used alternator my voltage will drop all the way down to 12.6v and fluctuates up to 13.5v (back and forth).
So I did the next thing changed the battery. Same results.
With new used alternator it hasn’t drop below 12.6v. So some improvement but still not at correct charging voltage.
And only seems to happen when my car is fully warmed up not when cold.
Has anyone had this problem and figured out the solution?
Also I had NGK plugs and read that sometimes cause this problem.
I already changed them back the OEM plugs. No change.

c54u

mine is a 2007 auto, and basically have the same symptoms as you...when the car warms up the voltage drops....also when that happens and i look at my lights on at the back of the car, they flicker...and so do the interior lights. the headlights do not flicker.
i have had this for 2 years now and dealer says nothing wrong...

my car is stock

MARSC6

Are these voltages at idle? I know my voltage will drop to about 13v at idle with the AC on. But while driving it will stay between 13.5-14 depending on what I have turned on.

bolivar

I think we should wait for the real 'experts' to check in on this topic.

But, doesn't one of the 'computers' now control the charging voltage? In older cars there was a regulator built into the alternator, but hasn't this task been shifted to an external computer? This is where your problem may be.

Of course, where/what ever is controlling the charge voltage, I think it is temperature compensated. In other words, in colder weather, it's going to throw a higher charging voltage.

*VETTE*

Yes voltages are at drive/idle.
Dropping to 12.6v.
The thing is that if there was a computer related issue that is affecting the charging system I would get CEL or message on my screen.
But I do not get any of those.

MARSC6

What does your voltage look like while driving? As long as it is in the upper 13s I wouldn't worry. The voltage moving around could be from things turning on and off like fans.

c54u

anything?

GenuineSurprize

i have this same exact problem and im sick and tired of it. i check my voltage meter more than my fuel gauge. In the past I fixed it by getting new sparkplugs(i had aftermarket.) It fixed the problem for about 5 months until my alternator took a crap. I got a new alternator and a new battery and I still find myself in the same situation. My last attempt is to get new sparkplugs again. Dunno wtf to do anymore. Only prob I have ever had with the vette is battery issues. The dealer keeps telling me its my after market underpulleys but it would be a shame to spend all that money to change them back and still have the same results. From the looks of it though some of you guys are having the same problem and dont have underpulleys.

HyperX

That was my only issue with my base c6 before I traded it in. I got a new battery and problem went away for a month or so. It then came back. Changed plugs to stock, that didnt help. Dealer put in new alternator, and it still came back. However, I did realize one thing. If the battery was fully charged (after long trip) problem would go away for 2 weeks.

GenuineSurprize

same here. when i drive on long trips it stays at a high voltage for a few days. there after a few city trips and back to low voltage. im thinking of just keeping the car on a battery tender when its in my garage.

HyperX

I really think this is the solution...

BAMAGOLFER

One thing I have noticed is that voltage seems to be ok (13-14V) until my cooling fan (radiator) comes on and then BAM voltage goes to 11-12 volts. I have a Varam intake that does block the radiator quit a bit. It seems that when the temp gets to 190 voltage goes to ~12-12.5. When it gets to 220 voltage is in the 11's. I do have a cam and headers. I'm going to take the Varam out and replace it with a KB II & beehive. Hoping this will help cooling. Also going to check rad fan to make sure it's not binding, putting a greater load on the system.
I hope this helps

Kelly

P.S. I have also noticed that when on longer local trips the temp stays down and the voltage stays around 13-13.5

HyperX

turn on your lights and you will notice same thing.. its not just the fan, its the electrical draw.

BAMAGOLFER

I'll try that.
If I understand it correctly the fan is not just an on/off thing but increases via a percentage as it gets hotter. So I was thinking that if there was some binding it would cause an increase in current which would result in a higher voltage drop.

HyperX

I wonder if people that use C6s as daily drivers experience this?

GenuineSurprize

mine is a daily driver. problem is i do a lot of city driving and i dont think my car has enough time to charge. regardles though this should cause the voltage to go so low that sometimes im stuck somwhere with a dead battery.

eeeny

I think it's a design feature. The alternator has a built in regulator, but the ECU computer can adjust/override it. Maybe it's a gas saving idea, dunno. But I wish mine didn't do it. I'm building a kit car with an LS3 engine and I am using the same alternator as in my C6, I just didn't hook up the alternator computer control wire and it stays at 14.4v all the time. I tried disconnecting that wire on the vette and I get a DIC warning .. "charging fault" or something similar.

In another thread someone said it was because the battery doesn't need to be kept at 14.4v to be kept charged, but I would rather did, just to be sure ;-)

Gearhead Jim

Could running 14.4v all the time cause the battery to get overcharged/overheated? Overheat the alternator and cause it to fail too soon?

BAMAGOLFER

I don't think so. Other Vetts I've had always ran at 14-14.5 volts and I never had a problem.

Gearhead Jim

I haven't taken notes on my 2006 and 2009, but mine seemed to run fairly high voltage for a while after starting, then on a longer drive the voltage drops down somewhat over time. Presumably, voltage drops off as the battery gets charged.

Electrical scientists can tell us more...