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OT (Mostly) - Remember the Car Talk Puzzlers?

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  • OT (Mostly) - Remember the Car Talk Puzzlers?

    I'm subscribed to get the weekly puzzlers by email, and here's an interesting one. (Don't know if I'm still violating some law, even if giving full attribution, but it's on the web anyway. If I am I guess they'll haul me off to jail.)

    [Quote (from car talk)]

    We had a customer that came in with a Dodge van. And the problem was that the battery was going dead. He'd had a new battery put in because that's what you do.
    Then a few weeks later, the battery was dead again. He went out to start it one morning and turned the key. Click, click, click, click, click. Nothing would happen.

    So, he took it to his neighborhood mechanic. The neighborhood mechanic said, "You need a new alternator." Of course, this was the same mechanic who replaced the battery, so he had to say something different. If it were a new mechanic, he would have said to replace the battery again. But it was the same guy so, a new alternator. He puts a new alternator in and everything is alright for a few weeks.

    And then, lo and behold, a few weeks later the same thing happens again. Right to the click, click, click when he tries to start the car. New battery. New alternator. Click, click, click. He goes back and gets another alternator and another battery, all under warranty, of course.

    Each time they're putting in the best quality parts. Everything works. They put in a new voltage regulator and made sure the belt is tensioned correctly. There are no drains in the system. You know, the dome light isn't on, glove compartment lights...

    So, there he is with this problem. He has an electrical system. All of the parts are perfectly okay. All of the components in the charging system are fine. All of the wirings is fine. The battery is fine and there are no drains on the system. And yet every two or three weeks, the battery goes dead. When it's jumped, it starts to run. And if you charge up the battery fully, even without doing any other repairs to it, it may run again for two or three weeks. Until finally one morning, it's dead again. Click, click, click.

    The puzzler question is, what's going on here? I mean, other than the fact that he's spending a lot of money!

    Beyond that fact, what's going on technically to cause this?

    [End of Quote]
    Lynn (Huntsville, AL)

  • #2
    To me going randomly dead every few weeks rules out a parasitic. I'd go for who left what turned on. A cell charger in a constant on 12v outlet?

    Comment


    • #3
      All the parts work, but is a bad connection included in the statement that the "wiring is fine"? It's not actually a part of a "wire".......... so technically it might be the issue and all the statements are still true.

      Then also, is the "wiring fine" if there is a wrong connection?

      The "generator light" may, if bad, stop charging of the battery. Are they including it in the all "charging system parts" are "good"?

      Other than that, yes, what got left on?
      CNC machines only go through the motions

      Comment


      • #4
        Ignition switch is failing

        Comment


        • #5
          I remember a '68 Wagoneer that stopped charging. After about a day of diagnostics it became apparent that the alternator wasn't getting voltage to the windings, thus wouldn't put out. Turns out the idiot light in the panel was burnt out. What???? There was no bypass resistor around the light so when the light burned out the voltage couldn't get to the alternator.... And of course the panel took about two hours to get out to change the bulb and another two to put it back in. Designed by an idiot!!!
          Pete
          1973 SB 10K .
          BenchMaster mill.

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          • #6
            A bad battery will kill an alternator, and a bad alternator will kill a battery. At this point he needs to replace both at the same time.
            Kansas City area

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            • #7
              Originally posted by Toolguy View Post
              A bad battery will kill an alternator, and a bad alternator will kill a battery. At this point he needs to replace both at the same time.
              He did. ...see last sentence of 3rd paragraph.

              Here's the answer they give:
              [Quote]
              Well, the truth is there was probably nothing wrong with the original battery. What was wrong was that the alternator was in fact faulty. The first alternator the mechanic replaced was indeed the right alternator, but it had the wrong size pulley. The pulley was too large in diameter and wasn't turning fast enough.
              [End Quote]
              Lynn (Huntsville, AL)

              Comment


              • #8
                [QUOTE=lynnl;n2000692]

                He did. ...see last sentence of 3rd paragraph.

                Here's the answer they give:
                Well, the truth is there was probably nothing wrong with the original battery. What was wrong was that the alternator was in fact faulty. The first alternator the mechanic replaced was indeed the right alternator, but it had the wrong size pulley. The pulley was too large in diameter and wasn't turning fast enough.
                [End Quote]
                ya know, (per the original quote) tom & ray said “All of the parts are perfectly okay. All of the components in the charging system are fine”

                I would take that to include things like the pullty and belt are the correct size and the belt tensioned properly, the belts weren’t slathered with grease, etc, etc. when they were on the radio they did this a lot

                frank






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                • #9
                  Well Tom and Ray took a lot of pride in their obfuscating skills.
                  Lynn (Huntsville, AL)

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                  • #10
                    I loved those guys. Saturday in the tractor with radio on just isn’t the same.

                    Comment


                    • #11
                      The answer is rather dubious. Sure fifty years ago with a dynamo it would be likely but one of the features of alternators is that they do provide a charge at low revs. More likely with a modern car is that condensation is settling on a circuit board turning on some item partially. I've had this after parking facing the wind during a gale. Another common problem affects little old ladies' cars that only do 3 miles a day each way to the shops with a stop at their daughter on the way so don't get time to recharge after the starting current.

                      Comment


                      • #12
                        Originally posted by SVS View Post
                        I loved those guys. Saturday in the tractor with radio on just isn’t the same.
                        I download their podcasts (two reruns each week) and listen while cycling.

                        Comment


                        • #13
                          Something which I've never heard a mechanic talk about, but which I've had direct experience with in my own vehicles and others is the wire that goes from the battery negative to the body, usually the fender or some place close to the battery. That's maybe an 8 gauge wire or similar, and usually a foot or less in length. A poor connection at either end of that wire can cause lots of symptoms. It takes little time to renew the connection at the body end, and it's a good maintenance item to perform once in a while. Of course, all heavy current-carrying wires should be making tight, low resistance connections. A dirty or somewhat dirty engine with some oil around these connections can cause weak charging, even if the alternator and battery are good.

                          What else can be involved- is there a car stereo system in the vehicle? Usually an amp gets a direct battery connection, and yours may not be shutting off if it's not wired correctly. I've seen this a few times. And don't rule out a hard-starting engine coupled with short runs, say the corner store and back- or a habit you may have of leaving the radio on for a dog while you shop. You just might find that it's you causing the problem. I'm not blaming you, just saying that sometimes it really is an operator problem.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            I really have serious doubts about the wrong size pulley diagnosis. If it were so much different from the correct size to cause insufficient charging, it would probably be impossible (or darn difficult) to mount the belt and tighten it. However, if the groove was incorrectly sized for the belt, it could slip, but that should be apparent when tested.
                            http://pauleschoen.com/pix/PM08_P76_P54.png
                            Paul , P S Technology, Inc. and MrTibbs
                            USA Maryland 21030

                            Comment


                            • #15
                              Originally posted by darryl View Post
                              Something which I've never heard a mechanic talk about, but which I've had direct experience with in my own vehicles and others is the wire that goes from the battery negative to the body, usually the fender or some place close to the battery. That's maybe an 8 gauge wire or similar, and usually a foot or less in length. A poor connection at either end of that wire can cause lots of symptoms. It takes little time to renew the connection at the body end, and it's a good maintenance item to perform once in a while. Of course, all heavy current-carrying wires should be making tight, low resistance connections. A dirty or somewhat dirty engine with some oil around these connections can cause weak charging, even if the alternator and battery are good.
                              ................................
                              On the old (long gone) S10, the battery had side posts, actually side contacts, there was no post. The wire was bolted in place, and IIRC there was a lead washer or spacerbetween the battery and the terminal.

                              Initially, the connection must not have been made up well, since it came loose and caused a number of intermittent problems until it was found and made tight. I was surprised that it did not blow the rectifiers in the alternator, but they were OK. The culprit was actually the plus wire, not the negative to the chassis, but that would also be a good candidate for causing problems.
                              CNC machines only go through the motions

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