View Poll Results: BATTERY OR ALTERNATOR?
BATTERY
0
0%
ALTERNATOR
22
100.00%
Voters: 22. You may not vote on this poll
Battery Or Alternator?
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Battery Or Alternator?
2001 F-250 7.3L DIESEL - BATTERY OR ALTERNATOR?
When my battery warning light came on, I figured it was time to get new batteries. I drove the truck for one or two days. Then when I tried to start it the next morning nothing...Dead battery, warning light lit & battery gauge reading low.
I bought two new replacement batteries & installed them.
The battery warning light still remains lit, but the battery gauge reads normal.
I am able to start, drive, use the headlights & normal features of the electrical system.
When the truck RPM pings above 2000, the warning light goes out.
From what I understand an alternator does not increase voltage as the RPMs increase, so I should notice no difference.
I checked the serpentine belt, it appears to be snug & in good shape.
Any suggestions before I visit the repair shop?
When my battery warning light came on, I figured it was time to get new batteries. I drove the truck for one or two days. Then when I tried to start it the next morning nothing...Dead battery, warning light lit & battery gauge reading low.
I bought two new replacement batteries & installed them.
The battery warning light still remains lit, but the battery gauge reads normal.
I am able to start, drive, use the headlights & normal features of the electrical system.
When the truck RPM pings above 2000, the warning light goes out.
From what I understand an alternator does not increase voltage as the RPMs increase, so I should notice no difference.
I checked the serpentine belt, it appears to be snug & in good shape.
Any suggestions before I visit the repair shop?
Elder User
Joined: Mar 2004
Posts: 509
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From: Pasco, WA
A good alternator's voltage will be close to correct (13.6-14.2) near idle. An alternator with a bad regulator will have low voltage at idle, but will increase the voltage as the speed picks up. I had a similar problem near the end of last year; dim lights & low voltage reading at idle, with improvement as speed picked up.
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Enjoy FTE....and
JOIN CLUB FTE -SUPPORT THE FORUMS!
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Logistics Pro
Joined: Jul 2002
Posts: 4,821
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From: South Dakota
The battery idiot light reads the output voltage from the Altenator, once it dips below a certain voltage it trips the light.
Generally speaking a poor set of batterys will cause a Altenator to work double duty to keep the batteries charged thus shortening it's life.
I try to reccomend that people should change out their batteries every years 2-3 or every 30-40K mi, this helps to keep the Altenator stress at a minimum. This is just a old habit that I picked up from my father.
Good to see that you've already replaced the batteries, all you'll need is a simple Altenator swap to solve your problem.
Generally speaking a poor set of batterys will cause a Altenator to work double duty to keep the batteries charged thus shortening it's life.
I try to reccomend that people should change out their batteries every years 2-3 or every 30-40K mi, this helps to keep the Altenator stress at a minimum. This is just a old habit that I picked up from my father.
Good to see that you've already replaced the batteries, all you'll need is a simple Altenator swap to solve your problem.
Senior User
Joined: Oct 2004
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From: Ridgecrest, CA
Here's a simple way to test the alternator, especially if the batteries are O.K. (they should be 12 volts or higher on each battery without the engine running and with them disconnected from each other). Record the static voltage, start the motor and the voltage level should be in the 13 volt range. If not, rev the motor up a little and see if the voltage increases. If it does, this generally means that some diodes are bad in the regulator and to replace it. One word of caution, when buying cheap rebuilt "lifetime warranty" alternators, I believe the company that rebuilds them only fixes the bad part. Which will lead to you using that "lifetime warranty".
Fleet Owner
Joined: Jun 2004
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From: Rio Rico, AZ.
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Update
I CALLED A LOCAL AUTO ELECTRIC...
HE SAID MOST TIMES IS NOT THE ALTERNATOR,
IT'S THE AUTO ADJUSTER FOR THE BELT
HE SAID TO TRY AND TURN THE FAN BY HAND.
I CAN FREELY TURN MY FAN, SO ACCORDING TO HIM...
IT'S THE AUTO-ADJUSTER THAT'S BAD
CAN ANYONE WITH A GOOD ALTERNATOR TURN THE FAN BY HAND?
IS THIS GUY REALLY TELLING THE TRUTH.
ANY THOUGHTS?
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Elder User
Joined: Mar 2004
Posts: 509
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From: Pasco, WA
The fan on a PSD is a heat-sensitive clutch fan; it will turn with minimal resistance by hand when the engine is cold. If you don't hear squealing when the engine's running, the belt's not loose enough to cause this problem. If & when you break the tensioner for the belt, you'll have no problem identifying it.
Postmaster
Joined: Oct 2004
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I'd also suggest you take it off the truck and carry it down to be bench tested. An auto parts store here claims the bench test is more accurate than the in the vehicle test. I bought a new alt after mine went out. A month or so later my alt light started intermitantly flashing. The parts store tested it in the truck and said it was fine. I instisted on a replacement and the light has not ever illuminated again. The parts store guy asked if I'd give him an update. Needless to say he's not impressed by his in the vehicle tester anymore.
Fleet Owner
Joined: Jun 2004
Posts: 25,090
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From: Rio Rico, AZ.
Originally Posted by SW_601
I CALLED A LOCAL AUTO ELECTRIC...
HE SAID MOST TIMES IS NOT THE ALTERNATOR,
IT'S THE AUTO ADJUSTER FOR THE BELT
HE SAID TO TRY AND TURN THE FAN BY HAND.
I CAN FREELY TURN MY FAN, SO ACCORDING TO HIM...
IT'S THE AUTO-ADJUSTER THAT'S BAD
CAN ANYONE WITH A GOOD ALTERNATOR TURN THE FAN BY HAND?
IS THIS GUY REALLY TELLING THE TRUTH.
ANY THOUGHTS?
Have you done the voltage test as suggested earlier in this thread? The fan will ALWAYS rotate freely with the engine off, it has no relationship with the alternater other than it's driven by the same belt! Please go do the tests as suggested earlier in this thread, I am sure you will find that the alternator is not charging at idle.
Senior User
Joined: Oct 2004
Posts: 374
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From: Ridgecrest, CA
I'm an electronics tech (did I spell it right???) and went through the same problem with the parts store checking an alternator. The testor has to put the alternator under a "max load" test to see if it can put out the desired current. One resistor required for this are fairly big, about the size of a small town's local paper. For a alternator that will put out 13.5 volts at 20 amps, the resistor will have to dissipate 270 watts. For the same voltage, but at 30 amps, it has to dissipate 405 watts. The way we get around this problem is to have several resistor in parallel (and they are still of decent size), but enough with the geek stuff. If the tester has an output current gauge, it might be a true tester, but I'd still have to see the load big load resistor (which I don't see as feesible) or multiple semi-big resistors (the more likely set-up in the tester). All this info also applies to battery checkers, but I believe they're designed to do a sample check for how quick the battery voltage degrades for a certain load. Now back to the beer.
ya done good roaky81 ! 
Freshman User
Joined: Mar 2004
Posts: 39
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From: M.W.Ontario
But lets not forget the battery cables, we had this kinda problem on a 2000 SD 7.3L that wound up staying on ouur lot for a birthday. Every time we would show it to a potential customer, it would not start. First 1 battery, then another , then an alt. turned out to be a simple cable connector, the postive side of the main battery.