Alternator or Battery?

[Pointer]

One or the other is going bad and need advice on which. When truck was new the voltmeter would go to about 16 volts at start up. Lately it has been going to 11 at start up and going higher only 20 or 30 seconds at idle or immediately if I start driving. It starts the same number of cranks as always. Two years now on the battery and I thought that seemed a little early. Also, which battery would be responsible.

[3-Fan]

Mine voltmeter acts the same as yours. Has since it was new. Don't think either one is going bad. Just lower voltage at start up.

[chuntag95]

Mine has always dropped at start and then come back up to a little over 14 Volts after 20 to 30 seconds. I have never seen 16 and would be worried if I did. The Voltage Regulator should hold the system below 14.5 Volts. Much more than that and you will hurt the batteries. The intial start puts quite a load on the batteries and it takes the alternator about 20-30 seconds to recharge the battery. After that, you should see a steady voltage, unless you are pulling a lot of current with a wench or some other high electrical draw. I read about people with plows having lower voltage. Just my 0.02.

[woundedbear]

Seems normal...

http://forum.62-65-dieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=3&t=003831&p=

[FirstDiesel]

There is a heater in the air circuit that is turned on for the first 20 seconds or so of run time. When it turns off the voltage goes from around 11 to around 14. 14 is normal. 16 is too high.

[Dan12]

I took mine to the dealer when it was new for the same thing. I was told this was normal for the Dmax.

[DmaxMaverick]

Sounds like the glow and heat grid cycle. Normal. The time will increase as it gets colder. If it's cold out and the engine is at ambient temps, you have a problem if you don't see the drop.

In the summer here, at 90

[Pointer]

Thanks, no need to worry I guess.

[letsgo]

Most vehical volt meters are just a heating element that is sensative to voltage variations and the needle is attached to a bi-metalic strip that bends from the effect of the heating element. (not to hi-tech and cheap)
you need to use an anolog or digital voltmeter and take the voltage readings from the battery terminals.
my readings are
voltage before starting 12.7
cranking voltage 11.6
30 seconds after start voltage goes from 12.4 to 14.6 and is constant.

dont just replace one battery you should replace both at the same time, or the new battery will start back feeding or charging the old one, unless you have diode protection as used in the marine multiple battery setup. I dont believe the dmax has diode protection (dont have schematics)
good luck

[ 10-16-2002: Message edited by: letsgo ]</p>

[TXMAX]

You shouldn't be seeing 16 volts at all. If you are there might be an intermitent problem with the voltage regulator. The glow plug relay will hold the voltage down right after you turn the key but then it (volt meter) should rebound to about 14-14.2 volts. If it stays much above that for extended periods the batteries will gas and since they have no caps for you to add water they will die prematurely. My .02.