I should specify that this is a new issue, not something stemming back to any fan or Fitech install. This voltage craziness is only the last few weeks. I initially thought the alternator was going, but I kept having to jump start my truck, and would get above 12.6V once I would have it running. So I assumed that there must be a bad cell or something in my 5+year old battery, and decided to replace that first. New battery and truck fires right up, but I started seeing the slow voltage decline again. Well, new alternator then.
Put the new alternator in and drove to the parts house and had them test the old one. Passed... new alternator is acting the same as the old (still good) one.
While driving my fans rarely come on. I have a 195° t-stat and big block radiator, the fans are set to activate at 203°. The temp reading on the FiTech sits at 198-201 while driving. Appears as though the airflow through the rad is plenty to maintain temp as long as the truck is moving. Once I sit in traffic, then the fans will activate as necessary.
The fans are the same ones I have had for several years, I think they are Mr. Gasket brand, 14". Both the same.i don't remember the exact amperage draw they have, but it was between 15 and 20 starting amps each, and under 12 running amps. I remember because I decided to fire them with 2 relays instead of one, because a single 25 amp relay wouldn't be enough to fire both combined, would've worked at runnimg amps though.
The alternator (TBI 105 amp that every early 90's truck got) has a sticker that states 74 amps at 2k rpm and 118 at 6k.
I am assuming that this is alternator rpm, and not engine rpm, mainly because the alternator pulley is so much smaller than the crank pulley, it has to be turning 2k+ rpm while the engine is idling at 750...
The fans being on or off had no bearing on the fluctuations of voltage, other than the voltage would fluctuate .2v lower. Still fluctuating, just lower than fans off because of the load.