Alternator problem?

Idiot (battery) light came on while out the other day. Alternator is putting out 12.66 volts upon start up and 15.2 volts after warming up. Battery won`t hold a charge over night . Alternator is 1+ years old. Has the alternator just gone and fried the battery too? Or could something else be causing the problem? The water pump was also leaking but was turning freely.

What voltage before startup in the morning? You said it won't hold a charge, does that mean it won't start or it has low voltage? If it just won't start, I would look at battery cables, connections, and ground straps. If the voltage is low, new battery is probably in order.

98stocker said:

What voltage before startup in the morning? You said it won't hold a charge, does that mean it won't start or it has low voltage? If it just won't start, I would look at battery cables, connections, and ground straps. If the voltage is low, new battery is probably in order.

Click to expand...

That's my line of thinking - the battery probably has a dead or dying cell, which will cause significant internal resistance and overnight draining. Your alternator output voltage sounds a little high - either it's overcompensating for the flat battery, or it's high and killed it off. I'd put a charge on the battery overnight, check the alternator output voltage after it's started up, and see if it's a little lower. Nominal alternator output voltage should be 13.5-14.6VDC - much higher than that, and you're looking and a battery killer - but, as I'd said, it's possible that the alternator voltage is running a little high at the moment because the battery is flat, and the alternator is running full output to try to catch up.

Check it soon - a flat battery can kill a good alternator.

5-90

Ok I finished to waterpump today and replaced a couple of hoses. I also installed a brand spanking new battery. Battery light came on instantly. I checked the alternators voltage (multimeter with neg at the battery and positive on the lead at the alt.) and the magic number was 19.17 volts. New alternator time? Or could there be something else? HELP or the heap gets it!

The old style Delco's used to do that on occasion. It was usually the regulator in the Alternator. I've heard of the CS type alternators charging a little high, but not that high.
If you run it very long (or at all) that way, something is likely going to burn up.
I've heard of people burning up most every builb in the lighting system before with runaway alternators, high voltage can't be good for the ECU and other stuff.
My CS (alternator) service info says if the voltage is above 16.0 volts the rotor field is shorted or the regulator is defective or both.

It took a new alternator and battery, but its done. Thanks everyone!