Hi guys,

I am experiencing voltage drop when the car warms up. At startup, the voltage is nice and strong at 14. After 15 minutes or so the voltage will drop steadily to 12, and you can see the voltage drop further when accessories are running (especially cooling fans and power windows). If the rpms drop (i.e. to 500 or so when starting from idle at a light), the voltage dips.

The car starts fine in the morning, this voltage drop only happens after the car has warmed up.

One thing I have noticed is that when I turn the car off and use the power windows, voltage drops way down to around 9 or 10 volts. Could this be a bad battery maybe? or maybe the alternator just isn't charging it enough while the car is running.

Thanks guys

 

How old is the battery? As they age, the plates get coated and reserve power will dwindle. It is normal for the gauge to show high volts after start up, because it is trying to replenish the power lost by the heaviest drain on the battery-the starter. As it warms up, the battery charge is slowly being restored and therefore the alternator will not put out as much voltage. It should not go down to 12v when the engine is at proper idle rpm. If the idle happens to dip below normal idle, you might see the voltage around 12v.

You should also check the system with a meter to see if the gauge is indicating correctly.

I have not really watched the voltage when the engine is off and the windows are being operated, but nearly everyone's windows are slow when the engine is not on.

 

yah I have the same problem.... When cold the battery is at the last mark or 3/4 mark and holds steady. If I push on the brakes it will not dip down, not if I am im drive and tap the gas the gauge does not move. But once it warms up a little bit not saying fully warm the gauge is now half ways between middle 13 and 3/4 and then when I press the brakes it will take a dive just below 13 and if i try the gas brake when stopped the gauge drops. So i dunno..


new coil, New alt, year old interstate 1000cca batt. redid all connections to big 3 except the motor to chassis.

 

with the car off, you will never see 12v when using any accessries. i wouldn't worry about that. if u want to check the battery, drive the car a bit and then put a volt meter across the leads. 12.6 volts would be perfect, but realisticly anything over 12 is okay. at 12 volts, your battery is roughly 70-75%. have your alternator checked....gm's have problems with voltage regulators, but those usually cause high voltage and make the alternator work harder. all this can be checked.

 

With vehicle at normal operating temperture, the alternator should read around 13.8~14.2, give or take a point....

Have the battery load tested.. A cell might be getting weak....

 

FWIW, I had the exact same problem and it turned out to be a failing alternator. Best bet would be to have both your battery and your alternator checked. Who knows, your problem could be one or the other, or even a combination of both. Either way, those are the first two places I'd look if I were having your problem...