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Car Repair: Alternator or Battery?

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  • Car Repair: Alternator or Battery?

    My girlfriend's Ford Explorer (2003) is having trouble and I'm trying to do things as cheaply as possible until I can scrape up enough money to get to the mechanic. My budget is very tight. I'm living paycheck to paycheck. When I get my finances squared away, I plan to get it fixed properly. Right now, I just need to get the car on the road.

    We were driving along and, all of a sudden, the engine just died.
    It was only about 1/4 mile from home so we pushed it back to the driveway.

    At first, I thought it was the alternator. I replaced it with one from a wrecking yard. ($25 vs. $150 from the auto parts store.)
    Charged up the battery using an external charger. The car started right up.

    I took it out for a spin and noticed that the volt meter on the dash board was reading only a little bit above the bottom red line.
    The needle should be somewhere in the middle of the scale. Correct?
    (There are no numbers on the scale. Only "H" and "L" with red lines above and below.)

    I'm trying to determine whether the car's battery is bad or if the alternator and/or charging system is bad.

    I used a volt meter and took some measurements from the battery terminals:

    • Engine OFF: 12.18 v (A little low but in range. Should be between 12 v and 13 v.)
    • Cranking engine: Drops below 9. (To be expected. Just so long as it doesn't totally conk out.)
    • Engine RUN: 11.75 v (Too low. Should be between 12 v and 14 .)
    • Turn ON Lights: 11.50 v (Lights are visible. Not too dim but it's daytime out. Hard to tell. It's brighter than just the filaments glowing.)
    • Turn lights OFF: 11.75 v (Normal for the situation.)
    • Measure from alternator post to battery while RUN: 11.78 v.

    I'm wondering whether replacing the battery would solve the problem or whether a bad charging system would just kill a new battery.

    I have a hunch that it's just a completely dead (sulfated) battery.

    When I brought the battery into the basement, I hooked it up to a charger and the ammeter only read 1-2 amps at first.
    It took 10-15 minutes for the meter to go up to the usual 5-6 amps.
    I disconnected it and let it rest for several hours then reconnected it. The meter immediately went up to 5 amps as I expected.
    I let it charge overnight. By morning, it went back down to 2 amps. I disconnected it and let it rest for a couple of hours before installing.

    When I put it in, the engine fired right up. No hesitation at all. Just like it should.
    I took it out for a test drive and that's when I noticed the low voltage meter. I high tailed it home before it could stall again.
    The car has been in the driveway, since.

    I'm trying to figure out whether I have a faulty charging system or whether I just have a sulfated battery.

    If the alternator/charging system is bad, I'll wait until I can scrape up the money and get the car fixed.
    My mechanic is only a couple of miles down the road. I can charge the battery up and drive it there with no problem.

    If it's just the battery that's not taking a charge, I can go to the wrecking yard and get a replacement for $25.
    Then, when I have the cash, I can go get a new battery from the auto parts store.

    What do you think? Is it just the battery?
    I'm leaning in that direction but I want to be sure.

    Last edited by Randy Stankey; 03-11-2020, 01:22 PM.

  • #2
    I believe you had poor luck at the junkyard and bought yourself a second bad alternator. The battery showing 12.8v with no load is a normal battery and enough to power the alternator field winding and get the alternator to output. Normal output from a properly functioning alternator in a running vehicle should be 13-14 volts and thus 13-14 measurable volts at the battery posts in a running vehicle. The amps shown on a battery charger indicate how many amps the battery itself is absorbing. A dead battery that has bad cells will not absorb any amps from a charger. Jump starting a vehicle with a stone dead battery and a good alternator will put heavy strain on the alternator but it would be capable of powering the vehicle until you shut it off again. Hope this helps. P.s., chain part store rebuilt alternators are terrible and do not last. If you can find a hole in the wall shop that rebuilds alternators and starters go with them. If you must rely on a part store alternator get one with the most generous warranty you can as you will need to leverage it.

    Also what usually fails in an alternator are the diodes in the voltage regulator. If you are feeling adventerous you might try opening it up and then ordering replacements from digikey and put em in. Might get you back on the road for a few dollars.


    • #3
      If you must rely on a part store alternator get one with the most generous warranty you can as you will need to leverage it.
      I second the motion that it's probably a bad alternator. If you buy one at a parts store, we always recommend that you get a NEW one, not a rebuilt. Also be aware that there are various quality levels...... for example, Carquest offers a "good, better, best" alternator options. The "best" one is the all-new one. The "better" has a recycled outside case, but the guts are all new. The "good" has some recycled parts throughout. These are the ones that give the rebuilts the bad reputation, because people tend to buy based on price. We don't even sell those unless the customer specifically requests it. All of the major auto parts chains offer a similar type of "rotating electrical" options, and all are about the same as far as quality.


      • #4
        When I said I was leaning in the direction of it just being a bad battery, I should have said that I HOPE it's just a bad battery.

        When I saw that the voltage from the alternator post to the battery was only a hair bit above the battery, I was afraid I got another bad alternator. I guess I'll have to go back and get another one.

        Yeah, I know that you take your chances when you buy parts from the wrecking yard but, right now, I've got to do this as cheaply as possible. I can make a complete repair later when I've got more money.

        Luckily, the place I bought the part from has a 30 day exchange policy.

        I didn't take the old one back for the deposit, yet. That'll get me another $10 to play with when I do.

        Replacing the alternator wasn't a hard job, really.
        The only crummy part was releasing tension from the spring loaded idler pulley.
        You need to put a 3/8" breaker bar in the center hole in order to pull it back.
        Actually pulling it back isn't hard. It's getting the wrench into the tight space that's the PITA.

        If it wasn't for that, the whole job would take less than an hour, including "bevarage service."

        Thanks for the advice!

        I'll try to keep posted.


        • #5
          Most auto parts stores (AutoZone, etc.) or even a Ford QuickLube will do a test on the battery for free or very little cost. They can see if there's any life left to it, but I'm not sure if what they would do is more in-depth than what you've already done.

          It appears that your battery isn't able to hold a charge, which would tell me that it's done. If it's more than 3-4 years old, that wouldn't be surprising, but maybe that's more of a factor here in the northern states where the cold is more of a factor.

          When our Explorer needed a new battery, I checked around and ended up getting it from Ford directly. They had the best warranty, and the price was the best overall value, especially after applying the Costco Auto Program discount. I can definitely empathize with your need to do it on the cheap, though. Just be sure that you're not pouring any amount of money into a bad part, because that just puts you further away from being able to get the part that will actually get the car back up and running reliably.

          Good luck!


          • #6
            I just took the alternator out again. It's ready to take back and get a replacement.
            They've got a 30-day exchange policy.

            I'll have to do the rest tomorrow. I work on second shift, now.
            That makes getting things done, during the day, harder to do because I get done working when everybody else is already in bed.

            Yes, I do think the battery is weak but I think it's got enough life left to get the car running until I can get a new one.
            If I can get the alternator working well enough to keep the battery alive, I can keep the car on the road.
            When I get enough money saved up, I can just tell my girlfriend to take it to AutoZone, buy a new battery and they'll put it in for her.
            Or else, I can get another battery and do it myself.

            When I'm working second shift and I only have one car running, I have to do all the shopping and errands in the morning and afternoon before work. It's difficult to interleave all of my stuff, the household stuff and getting to work. It's a real drain on time.
            Being tight on the budget just adds another degree of stress that I wish I could make go away.

            I've been working a series of crappy jobs for just barely enough pay to get by and all I seem to have time to do is go to work, come home to sleep then do it all over again the next day.

            This really isn't such a hard job for me to do. I used to do stuff like this all the time. Tearing down a movie projector and rebuilding it is a much harder job. Working at low-skill assembly jobs makes me feel like I'm losing my chops. Getting outside and putting my head under the hood of a car actually makes me feel like it's all coming back.

            I'll go out, tomorrow, and get another alternator.
            If I have time, I'll put it in before I go to work. Else, I'll do it Saturday.


            I'll keep you updated.


            • #7
              I just finished putting things all back together, again, and it looks like I have it running right.
              It started up, right away. Ran normally.

              Battery voltage - Engine OFF: 12.6v
              Engine RUN: 14.6v
              Alternator to battery - Engine RUN: 14.6v - 14.8v

              Headlights work normally.

              I took the car out and drove it for about a mile. Drives well.
              Volt meter on the dash board holds steady in the middle of the scale. (The scale has no numbers. Only "H" and "L.")

              It looks like we've got it running. Fingers crossed.

              This really takes a big load off my mind!

              Thanks for all your advice!


              • #8
                Takes a big load off your mind and... gets that big load on the road instead!


                • #9
                  Excellent Randy!