I have an 08 screw Limited with about 67,000 miles and still got the factory alternator. I'm curious on how long they usually last. I noticed on cold startups, my voltage is usually around 14.3v. After driving around for a bit, it will hover around 13.5 without a load. Now if im in drive with my foot on the brake and just my heads and foglights on, the rpms wpuld be around 580rpm's and the voltage is around 12v. Is that normal or signs of a bad alt? Im on my 2nd batt since i had the truck since new, batt is prob about 2 yrs old.

 

Nothing else is on ?
- EATC is off, not just on low.
- Radio is off ( it is stock, right ? ).

Might want to have the battery tested, to make sure it is not on the way out.
- You do not mention the mfgr of it

 

As far as life of alt there is no set lifespan. Depends on a lot of things.

Wouldn't worry about what reading is at when in drive and lights on. Sounds more like the battery is in need of replacement. Check the water level in the battery. Also take it to a auto parts store that can do a good test on it. Or take it back to purchase place and see about the warranty????

good luck

 

I wonder if it's as simple as a slipping belt? Snug when cold so higher charging, then looser as it warms up and stretches lowering the charging? Easy check and cheap fix anyway.

I'm more concerned to hear you're only getting a couple years out of a battery. That suggests something ( else ) wrong with the charging system. Or simply crap batteries.

 

Well the first batt was ford brand. I think motor craft. I never expect more then 5YRs out of them. So the second one was from advanced auto parts, their brand I think is auto craft. Its the same cca's as the stock batt. I just like to see a steady 14v but if iI am at a light waiting, the lowest I seen it go down to was 11.9 v. That's with heads and fogs, heat on med and radio on(stock radio).

 

The belt is snug as can be. Never had a prob with it slipping anyway, only when if I went thru a big puddle and it got wet.

 

I'll stop by advanced and let them do their test.

 

My '03 XLT 5.4 Scab still has the factory original alternator, with about 230,000 miles. Go figure...