I have a '99 f-250 with 170,000 miles. I'm here in colorado and its been cold the last two days, right around 25-30 degrees out. I went to work on Sunday and the truck was fine, it had been plugged in for the night and started right up. It sat at the job all day, and needed a jump to start it. On the way home the voltage meter was dropping. I turned of the heat, the radio, and anything that didn't NEED to be on. Once home I shut it off (after a 30 minute drive) and it would not start again. This morning it would not start. I removed the batteries and had them tested. They were both good. Re installed them into the truck (which had been plugged in all night) and it fired right up.... drove 45 minutes into work without incident. After work it was probably 35 degrees out. It started up. On the drive home I could watch the voltage meter drop. When I finally got home it was about 9 volts. I immediately took the battery ground cables off both batteries.

My fear is that the alternator is going bad and possibly draining the batteries while at a standstill ( possibly a diode stuck open?)

There are no warning lights on, no flickering lights, just a steady decline in the volt meter while driving. The lights, brakes, blinkers, radio, and fan all make the volt meter read lower, and show immediate change when shut off.

I'm guessing I made it home on battery power.... and the alternator is dying?? Is there a way to check the alternator without the engine running? I've got an ohm meter/volt meter if someone can give me pointers.

Thanks in advance,
Stevo

 

If the truck were an 02 and up you could use the instrument cluster to determine voltage through it. You could take the alternator in to a auto shop and have them test it. Most tests involved checking batteries and load test, as you have, and also starting the truck to see starter draw as well as charging amps. It should start at batt voltage and climb to 13.5+ rather quickly after the intial draw. My batt light didn't come on when my alt failed. An alternator can also check out fine voltage, but not be putting out enough amps. Maybe the internal regulator isn't working properly and it is dropping voltage or something...

 

I know you checked batts already, but if one is somehow bad it will kill your new alternator fast as well because it will always be trying to charge the batts... have they been load tested? Are connections clean?

 

I know you checked batts already, but if one is somehow bad it will kill your new alternator fast as well because it will always be trying to charge the batts... have they been load tested? Are connections clean?

 

Not an expert on the electrical but I think your alternator is giving up. Where in Colorado are you?

 

At 170K on the clock, my guess is your alternator brushes are pretty-well worn down, and the commutator rings likely have some grooves worn in them.

You could try simply replacing the regulator (which the brushes are a part of), but if the ring is deeply grooved, the alternator is in need of a new rotor.

Though these parts ARE available individually to repair your alternator, the smart money is on a complete replacement unless you have some specialized tools and knowledge.

There are some good brands out there that are much better and reliable than your auto parts house off-the-shelf ones are.

Pop

 

It dose sound like a bad alt, if all the contacts are clean on the batteries and you have charged them overnight and it still drains them, then I would get a new alternator and install it. This is the place that I got mine from High Output Ford Alternator, Large Case Alternator Upgrade for Ford 7.3l, 6.0 & 6.5 Power Stroke Diesel

I hate to volunteer people, but Pocket has AE and could scan the truck for codes and to see real time voltages. He might pop on and see this, and if he dose, I would be more then willing to by him beer for helping you and others out. He is local here in the Douglas County area.

 

Thanks for the replies. I got a new one today, and installed it.

Does anyone know the torque specs for the alternator mounting bolts?

 

Tighten until they go easy and then back off a half turn...

Sorry couldn't resist. I just snugged them up with an 1/2" ratchet. Been good for 3 months now.

 

I believe the torque spec in the manual is "goodentight", or if you are German "gutentight." FWIW when my alt. went I was driving down the road, no low batt or other warning lights came on but everything started shutting down- my guages on the pillar, A/C... I was in the middle of nowhere and fearing going completely dead before I got to a parts store but got lucky.

 

just tighten the bolts down, in the Air Force, we call it PFT!! Pretty Fn tight!! hahaha