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Rod Knox + Failing Rectifier = A+

I had written last week about my oil gauge that would fluctuate all the way to 0 and then go back up until the car was warm; then it would work fine. On this site, Rod Knox suggested that it was a failing rectifier in the alternator. I told our mechanic who was glad to try it. And this morning, he disconnected the alternator and drove the car . . . oil gauge worked flawlessly. So, although the alternator tested fine, we are replacing it, as Rod’s solution worked! Thanks to all of those who had suggestions for us, we solved this very mysterious problem - and I have some new vocabulary!!!

WooHoooo. Rox Knox is clearly not in the “chumps” category.

Mostly I want to thank you Karen, for your follow-up post. It is surprisingly rare and always great to hear how things turned out, and that problems have been solved.

WOW…FINALLY Someone took the time to tell us if one of our suggestions actually fixed an issue…LOVE TO SEE MORE OF THIS. We make excellent suggestions each day to try and help people and they all seem to just fade into the woodwork… How refreshing

I am proud to have been of some help, Karen. And thank you so much for posting your success.

While I was of no help on this one, I want to thank you for posting. I know Rod appreciates it as do the rest of us. We so rarely hear back.

Happy motoring.

You walked up to your mechanic and said, “I think my alternator has a bad rectifier” (more correct to say “a bad rectification diode”, but no one speaks like this much less a customer), what did the mechanic say back to you? A replacement alternator eliminated the symptom, is this as far as the “autopsy” went? Did the mechanic offer to look at how clean the DC was. Simple tests vith a digital multi meter would have been good to do before a alternator was slapped on.

I really suspect that you told the mechanic that the regulator was bad as no one says “your alternator has a bad rectifier” they may say “your alternator has a bad diode trio” but a "bad rectifier’ not common auto speak at all.

Well, our family has been with this shop since 1977, so we know each other well. I don’t have to identify myself on the phone, and I know their phone number by memory.

We have been working on this problem since the end of January. The first thing he did was put in a sending unit, since I hadn’t yet figured out that the gauge only fluctuated when the car was cold. The next morning it still didn’t work, so we tried another sending unit. Nope. I drove it for a few weeks trying to collect evidence to help him solve the problem, and he did a lot of research himself - but he didn’t get on Car Talk! After a few weeks, I gave him my information about when it was occurring. He cleaned all of the electrical contacts, checked many of the wires, and cleaned out all of the areas where oil might be sludgy. Helped, but didn’t fix. So he was stumped.

I was going to take it to the dealer, but they have just changed people, and I am not real keen on the new guy. So I came here. Several people suggested the oil pump, but we were pretty certain that wasn’t it. My husband was pretty convinced it was electrical, but neither of them came up with the alternator. When I called him last Saturday and mentioned the failed rectifier, his first reaction was, “Man, is that what it was?” Then this morning after he tested it, he said he had seen this once many years ago, but once he had headed down a trail of thought, it never occurred to him, since in the diagnostic test the alternator tested fine. Even this a.m. it tested fine, but he said after he put the new one on, some of the readings were different . . . so I think it was in the process of failing.

In answer to the “autopsy” question, I won’t know until tomorrow for sure that it works, because we only have a ten minute window. Once the car is warm, it works fine. But we are both hoping that it was the right move, and he thinks it is because the readings changed and the initial test of unhooking the alternator worked.

Anyway, when I walked in to get the car, I told the owner I was here to apply for a job! LOL.

Seriously, I may be wrong, but I think this board is made up of a number of people just like my friend who have seen many things, but collectively you all have seen everything! And between all of you, just about any problem can be solved! I am very grateful, because I honestly don’t think the dealership would have found it either . . .

If tomorrow morning I find the alternator still didn’t fix it, I will suggest using a digital multi-meter (though isn’t that what he did when he performed the diagnostic and checked the alternator?) . . . and yes, I did say I had a failed rectifier. They were not only impressed by my terminology, but they were impressed that I had thought of using this forum to find an answer. I am talking this site up to them and to my friends.

Thanks again for your help.

Kudos to Rod Knox, and congratulations to Karen!

If rectifier really meant “diode trio” what was happening was either the DC voltage had too large of an AC component or was an incorrect value (diodes can be made to perform a job called rectification). The odd thing is, is that they are seldom replaced one at a time, because of this people don’t usualy say “the rectifier was bad” they usually say “I replaced a diode trio”. Now if the part that was bad was really the alternators regulator (you can see how the words are similar) they do get replaced (if they are ever replaced at all) in a “one piece” setting. I really think it was your alternators regulator that was bad, but perhaps it was the rectifier “group”.