Hello Folks,

On my 6-cyl straight shift 2000 model F150, I've been getting the battery warning light coming on when I hit 2100 RPM. I don't recall having replaced the serpentine belt. I have about 82K miles.

I've tried to inspect if a pulley or bearing along the belt path might be binding. This occurs with the A/C on or off. I took it by a local auto shop to have the battery and alternator checked. Both were supposedly good.

Maybe it's time to replace the belt, but I'm afraid something is binding, too. Today on my drive in to work, it started happening at lower RPM, as well. Does anyone have any tips on how to isolate my trouble? Maybe it's not even the belt at all but a bad sensor, perhaps?

Thanks, all!

 

Sounds like the alternator is dying... The idiot light comes on when the volts fall below a set value.. Not sure what that is, since the volt 'gauge' does not ever really move...

If the light comes on at higher rpms, then you need to check the voltage at high rpms.. At idle, the Alt might be putting out > 13v, but when it's at 2000 or whatever, it's < 13v?

Belt would have nothing to do with it, unless it's slipping, but it would be squealing or you would notice the PS not working very well either...

My guess is a new Alt is in your near future..

What I would do is get a volt meter and check how many volts the battery itself is putting out (check this with the engine off). It should be around 12.0 - 12.8 volts. Start the engine and check again. It should now read around 13.5 - 14.5 volts. Have someone rev the engine to > 2000 rpms and see what it says... It should still be 13.5 - 14.5 volts.. If it drops, then it's a good guess, it's the alternator..

Mitch

 

Thanks for the suggestions. It occurred to me as well since my original post that there isn't any squealing of belts slipping. I went out and drove it at lunch break and noticed the warning light staying on all the time now. I've never experienced an alternator working properly at lower RPM but not at higher. Then again, I'm far from experienced working on vehicles. I figured an alternator to be an all or nothing device...it either worked or it didn't. So I started trying to see what else might be wrong.

I think I'll buy a new alternator on the way home (if I make it that far).

Thanks,
VolFan64

 

My '03 work truck had the battery light come on at higher RPM's (XL w/ no tach) for several months, and it turned out to be the alternator failing. Since the mechanics at work don't seem to want to fix anything until it won't run at all, by the time they replaced the alt., they also had to replace the battery (mechanic claimed the bad alt. fried the battery). FYI

 

When my alt went out, it did basically the same thing... Only came on when driving... Idle, the light went out. After a couple of miles of doing that, it just stayed on all the time. i checked the volts with the engine running, and I had a whopping 11 volts!

I stopped on my way home and got a 'new' one. Of course, it was dark and raining and I was 20 miles away from home and with traffic being very bad that night, it would have taken my over 45 minutes to get home... So, I ended up replacing it while parked in a car wash stall to stay out of the rain and it was pretty well lit as well. I had to borrow a breaker bar from a shop that was right there as well! Had it replaced in about 30 minutes (it was a real bitch to get the belt back on for some reason!).

If you don't have far to go and you turn off everything you can, you might make it!

Good luck!

Mitch