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I have a 2000 Toyota Camry with the L4 5S-FE engine. The car has 140k miles on it. When I first start it, the alternator whines fairly loudly. I narrowed it down by ear, then used the typical stethoscope and it sounds like a bearing in the alternator. (The whine is audible in the stethoscope when the tip is placed on the housing of the alternator)

I suspected the alternator was on the way out as coming to lights behind other cars, I noticed that once the car settled down to it's idle RPM the headlights would dim somewhat.

Side note: The noise is pretty bad when the car is first started, but gets quieter as the car warms up.

Thinking that the alternator could be on the way out I tested the voltage at the battery under various engine RPM as well as when the engine is off. Here are the results:

Engine off: 13.85 VDC (just the battery voltage, so the battery is healthy and charged). The table and chart list a high and low voltage because even without any RPM change, the voltage varied between these values. Probably from various things pulling current on and off. I didn't use an oscilloscope so I did not note any patterns in the variations.

Alternator output vs RPM

So, my questions:

  • Is the curve a healthy one for an alternator? (Keeping in mind the headlights were on low beam during the test as well as all marker lights)
  • Is the whine my early warning that one of the bearings in the alternator is going and I need to be prepared to replace it?
  • I realize no one has a crystal ball, but is there is typical time frame from the time the noise starts until I'm left stranded?
  • How serious is that 1/2 volt jump between 500 and 1000 RPM?
  • Does your engine really idle at 500RPM? Your data and graph have the min and max values transposed. – HandyHowie Feb 22 '16 at 14:19
  • Lol I never noticed that I reversed the line labels, ty. I'll fix that and repost. I have never measured the RPM with anything other than the tach in the dash so it's roughly 500 rpm. Could be 600 but it's too hard to tell at that range. – cdunn Feb 22 '16 at 14:43
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Is the curve a healthy one for an alternator? (Keeping in mind the headlights were on low beam during the test as well as all marker lights)

I would consider this about normal and quite healthy for voltage output. You'd expect the voltage to go up somewhat with the increase in RPMs.

Is the whine my early warning that one of the bearings in the alternator is going and I need to be prepared to replace it?

Considering what you've described, I think this is a good bet.

I realize no one has a crystal ball, but is there is typical time frame from the time the noise starts until I'm left stranded?

It could last another 10 miles or another 100k miles. Some alternators become noisy and die. Some become noisy and live forever. I'd suggest you shoot for the early mark and get this thing replaced. It will leave you stranded at the most inopportune time, just plan on it. There is no crystal ball, like you said.

As an alternative, depending on the manufacturer, you may be able to purchase the bushings/bearings for yourself and replace them. In most cases it really isn't a hard job to do and can be accomplished with a decent set of hand tools. Considering how well the alternator is producing the juice, this may be a good alternative to buying a new or reconditioned alternator.

How serious is that 1/2 volt jump between 500 and 1000 RPM?

That would seem fairly normal to me. Alternators are designed to run at operating RPM (above 1000 RPM). It seems to be putting out good voltage even at idle.

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    A great answer thank you so much. And thank you for the idea of buying a bearing set for it. I didn't realize that was an option. – cdunn Feb 22 '16 at 15:54
  • @cdunn - My pleasure. – Pᴀᴜʟsᴛᴇʀ2 Feb 22 '16 at 22:19
  • You are so right about the bearing set. I figure to be thorough I should replace the brushes and the brush holder, the regulator, and the front and rear bearings. Only thing that worries me is removing the pulley, and pulling / pressing the bearings. I do have a gear puller or two, but the price of the kit is up to over $50 and a reman unit from RockAuto.com is $100 after the core charge. I think I might save the time and let an expert rebuild this one for me this time around. When I have more time I want to experiment with it though. Just not on my daily driver.. lol – cdunn Feb 23 '16 at 17:00
  • @cdunn - Yah, one of those trade-offs. I had a starter on my 91 Suburban which went out (stopped cranking the engine). I pulled it apart, put a set of $3 brushes in it and was back in business. Saved me a ton of money over a remaned one and it worked for as long as I owned the truck. Rebuilding can sometimes save you money, but you have to sometimes place what your time is worth as well. – Pᴀᴜʟsᴛᴇʀ2 Feb 23 '16 at 18:02

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