When starting my truck, the factory charging gauge will stay on the line in between the 10 and 14 volts. After a couple of minutes, it will "slowly" move towards the 14 1/2 mark. Is this normal, or is my alternator going? I started my wife's 2007 Tahoe and upon starting it up, the gauge, at a constant speed, goes to the 14 volt or higher mark. My batteries are brand new Interstates I bought today.

:help:

It takes alot more juice to start a diesel with the intake heater and glowplugs, than a gas engine.

Sounds like batteries or alternator issue. I would put a charger on overnight and see if that makes a difference. Mine goes to it's normal position within seconds of starting.

Im sure your fine, how old are you batteries?

I am kinda curious about this one my self my 6.6 will start and run for about 20 seconds before the alternator kicks in, at least that's what the volt meter shows. I hope you get an answer soon so I can cheat off of your thread.

Im sure your fine, how old are you batteries?

I put two new Interstate Mega-Tron batteries, which have 800+ CCA, in my truck today. One at a time, I put a voltmeter on the batteries after having started the truck and it shows 15+ volts to both batteries. This should tell me they are getting charged, right?

Mine has always done this too I believe it is normal.

This is interesting......subscribed.

I am kinda curious about this one my self my 6.6 will start and run for about 20 seconds before the alternator kicks in, at least that's what the volt meter shows. I hope you get an answer soon so I can cheat off of your thread.

Yeah, of course this happens on a Sunday night, and I have to work the next 4 days. There is a Firestone shop, where I got my batteries from today that will run a diagnostic check on the alternator and starter to see if there is something wrong with them. For $25.00, I think it will be money well spent.

Keep in mind you are getting conerned over a very small change in a facory gauge that is a ballpark operation. I've heard it compared to measuring the bore of your piston with a ruler... it'll give you an idea, but its nothing to diagnose with.

It is completely normal. The ECM controls the voltage and while it is still unclear as to why it does not start charging the batteries immediately. There has been some theory as it waits until the glow plugs are out of the circuit as it seems to wait longer when it is cold. Once it starts charging it will run the voltage up to about 15 volts to put a charge back in the batteries then it drops down to about 13.9 – 14.0 volts.

If you where having a charging problem your DIC would tell you so.

Thanks guys. I guess I should rely on my DIC...........lol

The standard alternator (k68) puts out 105 amps max. Your glow plugs draw more than that. Unless you have a higher output alternator or have particularly warm temps, it is normal to have a voltage drop upon starting. That is why we get the pleasure of having multiple batteries.

i am going with glow plugs, both of my duramax's have done the same thing. Apparently when the glow plugs cycle off the load is released and the voltmeter goes up to 14

This charging delay has always been present with the Duramax. It definately is noticable, (or more noticable) when the weather gets cold.
Most here claim it is due to the high load of the glowplugs and air intake heater, which are needed, again, in the colder weather. I'm not sure I totally believe this, because I'm not sure the GP's are energized after Start-Up.

The other idea I heard several times, (but I don't know who could prove it), is that the ECM has a charging delay, which was designed to extend battery or alternator life in cold weather.
Again, I only heard this theory a couple of times and wouldn't know how to prove it.