Couple questions. 96 3.8L has always seemed the output was a little high, but never close to or in the red. My daughter started it the other day on a cold morning and said it got really close to the red, but slowly dropped back down. Can somebody please tell me what the normal voltage output should be if I placed a meter on the battery while at idle speed? I'm thinking it should be around 14.5 volts. Second question, Anybody ever replace a voltage regulator on the 3.8. I'm thinking it on the back under the plastic cover. I'm probably going with a new or rebuilt alt considering this on has over 100k... She does a lot of to and fro driving to college..

 

The voltage output level would be a function of the battery condition. If the battery was almost dead the voltage should be high to help recharge. If the battery is not drawing amps then the battery could fall down to 14 ish.

Check you battery voltage before you start the car, Then start the car and turn everything on. Now check the voltage again. Is it at or below the first measurment? Give it just a little gas, how is it now? If it falls back to or below battery voltage your alternator is shot.


This is a GM car, voltage Regulator are in the alternator as have been since the 60's.

 

Battery is a rather new (1 yr old) Interstate and low voltage is not the problem, it's just the opposite. Worried about overcharging I'm almost positive most alternators have a set output and do not fluctuate...

 

This is what I'm running with...figuring my voltage reading is okay if it's levels off between 13.8 and 14.8.....

 

Correction to the above video. That way isn't checking "alternator output", it's checking the input level at the battery.
To check the alternator output, you test directly at the alternator. There will be a difference between the two readings (higher at the alternator) due to having some power loss through the resistance of the car's wiring.

 

Thanks, do you have any idea what the output should be at the altenator?

 

Should be 14.4 ish. +/- a fraction

 

Voltage regulator itself could be on the edge of failing since you said it went high and then dropped to normal. In which case, you'd need a whole new alternator. I would still double check the battery to make sure it's not causing the alternator to put out excessive voltage. Just because it's new, doesn't mean it can't break. My battery is less than 3 months old and it almost didn't get the car started this morning....granted it was like -5 degrees out.

 

LOL, I am a GM master tech who has had voltmeters connected to 1000's of cars. It is going to take a lot of convincing to get me to believe alternators do not fluctuate. Auto batterys are tuff a hay wire regulator would fry the electronics in your car long before it could hurt your battery. Fact is the regulators are self monitoring, any failure should only result in no out put. I can't remember seeing a car with too high a voltage output since the 70s. I guess it is possible but it would be ultra rare. I have seen a few work orders that said voltage too high but that ends up being a gage issue. I can not even imagine the cost to repair a modern car that had too high of voltage put into it. The dash alone would be enough to total a car more than a few years old.

 

Thanks Gorn, I've been thinking it's the gauge, myself. Just trying to confirm by measuring the output. If overcharging, I would imagine GM has some fusible links in place to keep from doing major damage? Maybe? I'd hope so...