Alternator voltage after hot

[MegaMuscle]

Hey guys, yesturday while driving home I happened to notice that my voltage while driving on the highway at 65 was 13.0-13.2 volts via my ScanGauge. Once I noticed it I kept my eyes on it and even saw 12.8 twice in a 25 mile drive. So today I get in to get down to the local auto parts store to use their load tester thinking it is the batteries (2 years old BTW) and it is showing 13.8-14.0 like normal. Once the engine got above about 160 degrees WHAM volts drop to the 13.0 range. So I load test the batteries anyways and they both show 98% capacity and pass the test just fine. So I rip out the alternator and load test that at another shop here in town. Passes just fine. Have them do the batteries as well just to be sure and they said the same thing. Has any body seen this heat related voltage drop and is this an indication of an alternator heading south. I am looking at the DC Power Inc stuff and I just want to make sure this will solve the problem before I drop 400 bones on the problem. FICM voltage still never ever drops below 48.0 cold and 48.5 when she is warm. Nice and stable there but I know how fast these voltage issues can eat injectors and FICM. Any experience or advise would be appreciated.

[MegaMuscle]

Any suggestions?

[jd4010]

I monitor voltage via my CTS and although I'm usually in the 13ish range, I do see upper 12s (e.g. 12.8+) from time to time. I also monitor my FICM and it always runs in the 47.5 to 48.5 range with the average being closer to 48 even. So that said, I usually don't have any concerns when it runs in the upper 12v range.

It doesn't sound like you are having issues with the truck...as in starting and such. Correct? If none, I would just monitor it and especially the FICM voltage as well.

[MegaMuscle]

Thanks for the input. I was just really worried about the drop. I have not start issues at all and during the glow plug cycle is usually sticks right around 11.7-11.8 range. I think that maybe with the warm weather and the a/c and fan clutch maybe I am just not remembering how much load the summer can put on the electrical system. I have her back together and I will run it as I can't find an actual problem. I feel much more at ease knowing my numbers are not totally out of whack. Thanks again.

[mastaking]

next time try this check the votage at the batteries your will find that its about .5 higher mine shows 12.9 with my cts and when i check it at the batties its 13.5 and higer

[don_chate]

Sorry for resurrecting this old thread. Seeing the same results on my truck, SGII and 12V socket inside cab measures 12.8-13.2V at both idle and cruising RPM. New batteries old alternator, no battery light.

OP, did you end up replacing alternator by now?

[Galaxie]

I have a bit lower numbers when its hot. I am mid 13s and it can drop to low 13s. In the winter I watch it hit 14.0 now and then....

Yea, someone said it. Use another meeter as well.

[frakchered]

Originally Posted by MegaMuscle

Hey guys, yesturday while driving home I happened to notice that my voltage while driving on the highway at 65 was 13.0-13.2 volts via my ScanGauge. Once I noticed it I kept my eyes on it and even saw 12.8 twice in a 25 mile drive. So today I get in to get down to the local auto parts store to use their load tester thinking it is the batteries (2 years old BTW) and it is showing 13.8-14.0 like normal. Once the engine got above about 160 degrees WHAM volts drop to the 13.0 range. So I load test the batteries anyways and they both show 98% capacity and pass the test just fine. So I rip out the alternator and load test that at another shop here in town. Passes just fine. Have them do the batteries as well just to be sure and they said the same thing. Has any body seen this heat related voltage drop and is this an indication of an alternator heading south. I am looking at the DC Power Inc stuff and I just want to make sure this will solve the problem before I drop 400 bones on the problem. FICM voltage still never ever drops below 48.0 cold and 48.5 when she is warm. Nice and stable there but I know how fast these voltage issues can eat injectors and FICM. Any experience or advise would be appreciated.

Haven't noticed the drop, but did notice the heat. i will be sure to check mine once i get it back to see if it does anything.

[MegaMuscle]

Late reply due to being gone but no I never did replace the alternator. I have had it tested three times and everybody says its good and the batteries have been load tested 4 separate times now and they are always 99-100%. My conclusion is that as long as the batteries are getting enough to stay fully charged and I have no battery light I am good. I watch my FICM voltage like a hawk and I am always 48-48.5 on the SGII. If it ain't broke.......Hope it helps.

[WarChild]

Stock or rebuilt (dont recommend rebuilt) alt the volts can be anywhere from 12.5-14.0ish but should not be below 12.5. My rebuilt alt can see as low as 11.8v when the alt gets hot. They are not relyable. I have had 5 in the last 3 months and keep 2 spares with me while I am traveling. Will be getting a H.O. one after I get back to Florida. Really your alt should not go below 13.0v but on high demand with stock alt it can drop. I would say yours is fine.