Alternator, or something else?

01 Silverado, 160k miles original alternator. This morning I started my truck (about 28 degrees out) and I noticed right away the volt gauge was reading about 9v and the battery light in the message center was intermittently flashing on and off. Engine seemed to be at a low RPM for being a cold start. I revved it up a little and nothing - so I let it run for about 15 minutes until truck was completely warm. Still low voltage on the gauge - I put a multimeter on the battery and it read about 11v, dropped to 10.2 by the end. I got in the truck and revved it up to about 2200rpms and as soon as I did, the volt gauge fired right up to 14 like an oil pressure gauge would. It stayed there and battery now read 14+v. I drove to work and no issues, it sat for 4 hours and I ran out for lunch, when I started it at idle it sat at 9-10v again. I immediately revved to about 3000rpms and it jumped back up to 14v and stayed there. Ideas? Alternator going bad? It doesn't seem like the belt is slipping, tension is there. The battery is less than 2 months old also. Thanks!

Your alt may being going south. Before I would replace, I would check all battery cables for clean and tight. And connections on the alternator. Since you just replaced your battery, is it possible the cables aren't tight?

Your alt may being going south. Before I would replace, I would check all battery cables for clean and tight. And connections on the alternator. Since you just replaced your battery, is it possible the cables aren't tight?

Or clean.

thats how my 2000 SIL failed . the regulator is corroded. when driving I would notice the idle drop then the alternator/battery volts low.then it would come back. when it finally failed for a longer time I then checked this out to find that the alternator was indeed the problem . very easy job . most importantly get the new alternator. NO rebuild. these rebuilds are crap.

I got a delphi with the lifetime warrantee. 3 yrs now still good. I used the 105 amp as was OEM, you can get I believe the 130amp which is the same size/fit.

got at Autozone..

find a shop that rebuilds alts. you can get them rebuilt at there shop for about 1/2 the price of a new one. heck my local guy gave me a quote on rebuilding a genarator starter, it was in bad shape and i even told him, that it would need every thing replaced but the case when i called. the dealer wanted 700 bucks for a new one. when it was all said and done i got a brand new one for $350. when mine goes out the guy will replace every thing that is worn eh will start with bearings then the regulator and diodes.

find a shop that rebuilds alts. you can get them rebuilt at there shop for about 1/2 the price of a new one. heck my local guy gave me a quote on rebuilding a genarator starter, it was in bad shape and i even told him, that it would need every thing replaced but the case when i called. the dealer wanted 700 bucks for a new one. when it was all said and done i got a brand new one for $350. when mine goes out the guy will replace every thing that is worn eh will start with bearings then the regulator and diodes.

I got the delphi new lifetime warrantee alternator for 180.oo..

Dealership 700.oo for a 1 hr job with the 350.oo for alternator I guess they now charge 350.oo an hr..

Thanks for your help - the cables were clean and tight so I got the Delphi 105A alternator and guess what, problem solved! Thanks again.

Thanks for your help - the cables were clean and tight so I got the Delphi 105A alternator and guess what, problem solved! Thanks again.

thats good you got the new delphi because it has the updated voltage regulator.

good luck .