I recently installed 2 Duralast Gold series batteries. Both of them are reading 12.6V but when I start the truck the voltage drops down to 11.5V. So I guess I need a bigger alternator that can charge batteries. The question is: what alternator will give enough current to charge the batteries? 120amps? 140amps? Any help would be greatly appreciated.

 

The alternator will not charge when glow plugs are on. Wait a few minutes after starting then check voltage again.

 

Mine do exactly the same thing and I'm running a 200A alternator. Yours is pretty normal.

 

AGREED^^^^^^^^^^^

AT startup the first minute or so there is a HUGE Amp Draw upto 225amps or so. It does come down into the 140amp range Fast and eventualy settles to around 80amps or so if you have a Stock truck

If you have OEM Alt Odds are High its only a 110amp Alternator PEAK OUTPUT

So at an Idel the OEM Alt basicaly Falls SHort on Amperage


SO this ALL SAID^^^^^^^ its HIGHLY RECOMENDED to Invest into a High Output Alternator and do the Battery Cable UPGRADE

A High Output alternator will Extend the Life of ALL Electronics
BATTERYS
FICM
And so On

I run a 190amp DC Power alternator some of the Best Alternators out there and demand is so High that it may take some time to get it to you

DC Power does NOT Cut Quality to get alternators out the Door either so you can rest assured your getting a TOP of the Line Product

 

With a volt meter and stock alternator this statement appears to be true.
The glow plugs are saturating the output of your stock alternator.After a brief period, the glow plugs start to cycle off and your voltage rises.

 

V8 Guy, Your good to go. Enjoy the truck.