Pulley whine?

[dingobait]

1999 Isuzu Rodeo LS 3.2L V6 MT 272K miles

I've been hearing a whine for a few months now, but there have been no detrimental effects so far.

I replaced the serpentine belt idler-pulley last year when it went out screaming.

I used my mechanics stethoscope just now and it appears that the while "may" be coming from the serpentine belt tensioner pulley, which wouldn't be surprising since it has over 1/4 million miles on it and has spun billions of time.

Anyone else experienced this? It's been a few months or more since it started but nothing has happened (yet).

Thanks,
Mark

[StevenZ]

I had the same problem, so I told her to keep quiet or get out of my truck....


Seriously, have you tried temporarily removing the serp belt and running it to see if the noise goes away? Might be worth a try to help isolate it.

[dingobait]

Ha ha. Nice.

Yeah, I guess I could do that and run it momentarily so as to not overheat or run the battery down.

That would tell me whether or not it's serp belt related, since I can always hear it right away.

Good idea.

Thanks StevenZ

[dingobait]

That was a great first step.

I removed the serp and started it up, and the whine was gone.

Now I just need to figure out whether it's the auto-tensioner, idler pulley, cooling fan pulley, alternator, power steering pump, or the A/C compressor.

Since the standard mechanic's stethoscope has such a short reach and hasn't helped nail down the root-cause yet, the next troubleshooting step is going to be replacing the current serpentine belt with the non-A/C version.

A few people have told me that they've had A/C compressors that exhibited the whining symptom, and this is one way to rule it in or out conclusively. Even if it isn't the A/C compressor, I'll have another spare serpentine belt that can be used if needed, so worst case, the tool can become a repair part.

I'm going to let it cool off and then replace the belt first thing in the morning.

One thing that has had me puzzled so far is the fact that the whining can be made louder after starting it "cold" by turning on the headlights, and then the high-beams, and can be made even louder by holding all 4 window switches to the up position with the windows already up, essentially all just methods of increasing the electrical load, however that phenomena disappears once the engine is warm.

Once it's warm, adding more electrical load has no effect. The whining is steadily a bit louder once it's warm and doesn't vary with the load. For a while I wondered if the whining was associated with the alternator.

Well, I'll rule-in or rule-out the A/C compressor in the morning, and then dig deeper if necessary. I need to find the culprit before it siezes, smokes my belt, and has me calling AAA.

Any input appreciated. I'll post again once I have an update.

Mark

[StevenZ]

I'm assuming when you had the belt off and engine off you turned each pulley by hand to see if you could feel any roughness when you rotated them (bad bearing/bushing). If not, I would definitely do this next. The other piece that you added about the noise being more pronounced when cold and when there's an electrical load causes me to lean towards the alternator. Not sure if you've ever replaced it, but it might be worth checking it and the condition of your battery. When you first start the truck there is a draw on the battery from the starter. This would trigger more output from the alternator as would the other situations, e.g. headlights, windows, etc. While whining can come from bearings/bushings, it can also come from an alternator that has a faulty bridge rectifier (AC to DC convertor). I've also seen where a bad battery will place greater load on the alternator, even though the battery has enough energy to initially start the vehicle. That's why I mentioned you should check it along with your alternator.

If the charging system checks out okay, then my next point of interest would be the power steering pump. If it is low on fluid or just wearing out, it too can produce a whine noise that is more pronounced when cold - until the fluid warms up.

Hope this helps and will be interested in knowing what you find.

[dingobait]

It's definitely not the A/C compressor. Now I have another spare belt.

Yep. I turned each pulley by hand. Couldn't really feel any roughness. I removed the idler pulley and the tensioner pulley, but both seem find. I replaced the idler pulley roughly a year ago.

I broke out the stethoscope again and probed around. Naturally the whine gets transmitted throughout everything so I had to just search for the loudest point, which is definitely at the alternator.

I've suspected the alternator all along for the reasons we discussed in earlier posts. I'm going to see if the local Autozone etc will do a charging system check.

If I pull the alternator, they can likely spin it up as well and it's possible that the whine may be audible.

I believe that it's likely the bridge rectifier and not the bushings which lends it'self more to the electrical load amplifying the noise when first started cold.

I'll have the battery checked as well. It was replaced on July 4, 2010, so it's not new, but not terribly old, and it always starts strong, even if I leave the dome light on all night.

I keep very detailed records and it's amazing that I do not show the alternator as ever having been replaced, even after 15 years and 272K miles.

I've got to do a little work on my son's car for a few hours, and then back to mine.

Thanks StevenZ. It really helps to have someone else to bounce ideas off. Very much appreciated.

I'll post again soon with the results.

Mark

[dingobait]

The charging/load-test indicated a few bad diodes in the bridge-rectifier.

I replaced the alternator and the whine is gone.

I doubt this remanufactured alternator will last 272K miles, but it has a lifetime warranty so it's all good.

Anyone getting ready to remove the alternator can save a little time by removing the radiator fan shroud and the radiator hose (after draining the radiator of course), since those need to be out of the way in order to get the alternator out of the engine bay.

Getting the battery out of the way makes things easier as well.

Thanks for your input StephenZ. Very much appreciated.

Mark