I have the Navigator in my signature below.

Yesterday I let the truck idle for a long time, (about an hour) with both the electric fans running, (the Taurus cooling fan on the rad. and the cooling fan on the trans cooler)

I then went to the store and when I came out after the truck sat turned off for about 10 minutes. I turned the key to start it and it just clicked real fast. So I got out my portable car starter and let it sit on the battery a few minutes and it started it up. The starter turned over slowly but it did start. Just like it had no charge in the battery.

Drove it 5 minutes home checked the battery and it was low (its a new battery a few weeks ago ) on power.

Then I checked the alternator at the battery with the truck running and only got 12.85-13 volts coming to the battery from the alternator.

Inside when I do a diagnostics check with the indash service system, it says the charging system is ok.

I put my volt meter on my wifes car and it was putting out a good charge at around 14+volts while running. ('04 caddy)

Im stumped do you all think the alternator is going bad and just isnt charging the battery as well as it should anymore? I do have the 105 amp alternator in it and have 2 extra electric fans on the engine now.

Thanks in advance

 

I have gotten some numbers from my volt meter on this question above more details that is.

When I sit and idle my alternator is putting out around 13.18v when I turn on the AC it cuts down to 12.5v then with the AC and headlights on it goes down to 12.05v. When the AC fan, headlights, and trans cooler fan are on it drops down to 11.65v and keeps dropping.

With the engine at 2000 rpm the alternator with nothing on is putting out 13.25v. With the AC on 12.75v. With the AC and headlights on 12.25v. Then with the AC, headlights, and trans cooler fan on 12.05v.

I also went to the Autozone store here and had them test the trucks battery, starter, and alternator. While testing with no fans running and everything off, the truck passed all the tests with the battery being marginal. (It showed a full charge but was only showing 620 CCA when it is an 850CCA rated battery)

Now when the truck had the two cooling fans on and the AC running, it failed on the low voltage test coming out of the alternator. The amps the alt was putting out at idle was below 12 volts and kept dropping.

What do you guys think, is my alternator going bad in your opinion?

Also should I upgrade to a 130amp, and can I upgrade to a 130 amp? Just because I have more electric fans running now. My build date on the truck is 11/02 which at autozone calls for a 110amp alt. But for any Navigator built after 1/03 they call for a 130 amp alt. Can I just get the 130amp and it will bolt right up with the correct wiring?

 

Yes you need a new alternator and yes the 130 amp one would be a good idea because of the fans. I would also go up a size or two for the main power wire running off the back of the alternator. The original wire might not be able to handle the higher output of the new alternator.

 

Thanks alloro, I thouight that it was going bad. It seems that if the truck just has the AC and headlights on it is fine. but once the fan for the trans cooler comes on it jumps the VM down to below 12volts so I figured the alt was going bad.

 

I agree on the alternator, it should run 14 V at 2000 rpm, and the volts should not drop off as acessories are turned on.

I would also upgrade to the 130a, though I can't say for sure it would bolt in, I would try it.

I would also budget in for a battery. The bad alt has worn out your battery, and there is no point in working your new alt overtime to compensate.

I am assuming they tested the battery with a full charge?

 

Should the alternator *indefinitely* put out 14V? I watch mine with a multimeter and it starts charging the batteries at 14V after a start up. But after 30 min. or so, the voltage starts dropping ~ 13.5V.

I suspected the batteries were just charged back up, but I thought automotive electrical systems charge at constant voltage. So why the drop?

Thanks for the comments.

 

Hey BG,

So even though the battery is new a few weeks ago do you think it is bad? I had it chevked out and they said it was ok and fully charged.

 

If the battery passed a load test, it should be fine. It is not uncommon for a bad alternator to take out a questionable battery. Sounds like yours should be fine.

 

Ok thank BG

I got a new alternator today and installed it. It was rated at 135 amps and they bench tested aand it tested at 148 amps. I put the multi meter on it and ran all accessories and it came down a little bit from 14.25v down to about 13.8v so it should be good to go now. I was very happy with the place I got it from Motorcityreman.com and cheap too only 149.00 plus tax for a brand new alt. (they are in MI and shipping is free)

 

The alternator has a voltage regulator. This allows some fluctuation, but it's main prupose is to keep the voltage down around 14V max. More than that will damage the battery and possibly some of the accessories.

The natural state of the battery is 13.2V fully charged. Each of the six cells in a 12V battery produce 2.2V. What you are seeing is the alternator charging the discharged battery after a start up, the battery recovers and the alternator voltage drops off just maintaining the batteries 13.2V.

 

Thanks!! I just though it should stay at 14V. So it appears my system is working normally.