Alternator "groan"


Asked by Jan 01, 2016 at 04:56 PM about the 1999 Mercury Mountaineer 4 Dr STD AWD SUV

Question type: Maintenance & Repair

I have a 1999 Mercury Mountaineer. V-8 AWD.  It starts, and runs fine. However, it has developed a "groaning" sound, that I have tracked to the alternator, using an automotive "stethoscope".
I replaced the alternator, and the "groan" is still there, coming from the alternator. Could an idler pulley transmit this kind of sound to the alternator?
I'm out $150 for the alternator, cause I was positive that was the source of the noise. Now, I'm just baffled.

16 Answers


probably. take off the belt and check all the pulleys. should be able to feel a bad bearing.

2 of 2 people found this helpful.
Best Answer

a new alt with a bearing nose??maybe...idler pully maybe/// A BAD BATTERY WILL OVER WORK THE ALT ALSO...IS THE BELT GOOD/CLEAN/FRESH/GROVES/ DRIED OUT....

1 of 1 people found this helpful.

I checked battery with multi tester. Just shy of 12V with engine off. About 13.9 with engine running at idle. I should have known right then, that the alt was still good, but I thought it was the alt bearing. That's why I replaced it. Noise is identical, no change.

1 of 1 people found this helpful.

Usually a 'groan' or a 'growling' sound is the power steering pump, either low on fluid or on it's way out. Maybe you should try the stethoscope again, after checking fluid. it may not even be noticeable when turning, hard to turn I mean

7 of 7 people found this helpful.

The power steering pump was my first guess, but like I said, the stethoscope led me to the alternator. That's where the groan is coming from, just not sure what might be transmitting it there. Guess I'll have to go back out and pull the belt again, to check all of the pulleys.

2 of 2 people found this helpful.

Battery, engine off click for full screen

4 of 4 people found this helpful.

Temp is about 25F here.

2 of 2 people found this helpful.

Hmm, now I don't know what to make of that. If it starts ok, that 30% loss will be a 10% charge, and I just have a hard time with those figures. As long as it cranks over well. Unless I have it backwards, that same, we will call it 11.9V read ("Just shy of 12V") would be 12.3V above freezing and a 70% charge.

4 of 4 people found this helpful.

When I took my readings, I had just started the vehicle, and moved it into the garage. The chart says it should sit for 2 hours, to apply those numbers.

2 of 2 people found this helpful.

Pull the belt off and start it (don't run it more than a minute or so). Is the noise gone? If the noise is gone the problem is with something that the belt drives, such as tensioner, idler, alternator or a/c compressor bearing.

3 of 3 people found this helpful.

An alternator will sometimes be a little noisy when under load. With the headlights, rear defogger, a heater fan on high for example. But usually that sound is more of a high pitched whine. Power steering pumps on Ford Products tend to be noisy as they get older. Especially in the cold weather. Since the alternator is bolted to the engine you may be hearing the sound from something else. Like the water pump, or idler pulley as well. HTH. -Jim

1 of 1 people found this helpful.

Went up to my local parts place, had them give a listen to my Mountaineer, and they agreed the " groan" was coming from the alternator. Their opinion was, that the belt tensioner was applying excessive tension on the belt. It seems that a belt tensioner would get weaker over time, not stronger. Does their advice sound logical?? BTW. Thanks, to all of you that have responded to my problem.

3 of 3 people found this helpful.

Personally, makes no sense to me. A spring loaded tensioner will not tighten up over time. I suppose the center bolt, not the one you use to relieve tension, but the bolt that hold it on, could get moved.

3 of 3 people found this helpful.

I agree with Fordnut. A spring tends to get weaker over time. I do recall, years ago, a friend had a late '80s Thunderbird. We replaced the alternator in that car 3 times in about 3 months. All 3 were defective. There was supposed to be a spacer in between the pulley and the alternator body. During the rebuilding process this spacer had been removed and apparently discarded. In his case it kept chewing up the serpentine belt. It wasn't until he took it to the local Ford Dealer that we found out what was going on. They spotted it in about 5 seconds. It's not unheard of to get a defective product out of the box. Unfortunately it does happen. If you can, take off the alternator and have it tested on a machine. The noise will probably transfer to the testing machine if the bearings are bad. Especially if they can duplicate the tension of a belt being on it. HTH. -Jim

1 of 1 people found this helpful.

FYI.....My problem has been resolved. It was the belt tensioner idler pulley. It was transmitting the vibration to the alternator. My stethoscope was picking up the noise there. Swapped out the pulley, and it purrs like a kitten. Thanks everyone for the tips.

2 of 2 people found this helpful.

Awesome! Thanks for letting us know! Glad you found it! -Jim

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