The screaming fan belt from hell...

[mvtofino]

I am fresh out of ideas about what could be the problem. The alternator fan belt started squealing following the installation of a new alternator. Went back to the supplier to have it tightened; a few miles later it was squealing again, so back to the supplier a third time. We departed on a road trip to San Francisco, and got about 3 miles before the belt started howling again. Back to the supplier a fourth time. On the road again, made it across the border and 30 miles down the highway before it started screaching terribly. AAA dispatched an emergency road service guy who tightened it real good. Another 30 miles, it is screaching even worse. I had a Chevy dealer install a new fan belt that they made sure was tightened to spec. All went well for the next 1,500 miles, and then it started to squeal a little at low RPMs, but once revved up, the noise subsided. Over the next 1,000 miles, it started to squeal earlier and more often, but once there are a few revs, it smoothes right out.

Now for the last 500 or so miles, whenever the engine is shut down, the squealing starts all over again when the engine is re-started, and it continues to squeak at idle until she reaches operating temperature, then she quiets right down. It doesn't matter if the engine is shut down for only a couple minutes (at full operating temperature), or it is left to cool down overnight.

I have wondered if it was the wrong belt (both suppliers confirmed the right part number), or perhaps a pulley alignment problem, or it's just the belt heating up. But I've never heard of that before, and if it was pulley alignment, wouldn't it continue to squeal 100% of the time?

I would sure appreciate any ideas and/or input from others before this drives me around the bend. Could it have anything to do with the alternator charging at maximum output after starting the engine, and the extra magnetic field causes more resistence and then the belt starts to slip until the batteries are recharged and alternator output goes down? Just being creative...

Thanks in advance for your help!

JT

[DmaxMaverick]

It could be any number of things, or a combination of them.

New alternator....Perhaps its parasitic drag is more than it should be. Wouldn't be the first time, if it were bad out of the box. Nothing you can do about that, except replace it, again. Confirm it is the belt squealing, and not the alternator, itself. I've seen very many noisy reman's over the years. Some grind, some whine, some squeak, and some squeal like belt slip.

Bad battery(ies). Excessive charge demand will load the alternator more than normal. If you ran a long time with the (previous) bad alternator, the batteries may have suffered, or are in need of a really good full charge (which should be complete, by now).

Alternator pulley. Perhaps it's "too" smooth, or has some oil (or other substance) residue on it. Silicone (sealer or lube) takes a loooong time to "wear off". Scuff it up with some fine sand paper or a steel wire brush. Or, the pulley could just be bad. When I replaced my OEM alternator (on the 2001) with a high-cap aftermarket, I had a squeal issue. Mostly at shutdown (A/C on or not), but eventually more often at lower RPM's. Eventually, I replaced the aftermarket pulley with the pulley from the OEM (luckily, it fit), and now it only squeaks slightly during shutdown (more of a single chirp). The new alternator's rotating mass is about double that of the OEM, so some is to be expected. The OEM pulley is also larger than the aftermarket, so restoring the OEM pulley slowed it down a bit, as well as having more pulley surface area contacting the belt. The 2001 is a serpentine belt, but the characteristics between the two are about the same, when it comes to problems.

Belt/pulley alignment. Probably not an issue. If V-belts are out of alignment enough to cause easily noticed problems, like squealing, they will generally either derail, roll, or self-destruct very quickly. Overtightening a belt to overcome a squeal may destroy the alternator in the process. The bearings can handle only so much.

A squealing belt will self-destruct very quickly. Squealing is slip, and slip is heat. This will also effect all the other pulleys it contacts, causing a glaze that will eventually make them all squeal.

[Robyn]

The squealing after even a short shutdown is due to the alternator coming up top full output, and more drag than the belt can handle.

This happens due to the heavy draw on the batteries for the startup.

As Maverick mentioned, Batteries may have issues, but I am inclined to believe that the alternator is Hinky.

If this were my rig, I would replace that alternator with one from a different source.

These rigs with the V belt drives always had some issues with the belts but not to the extent you are seeing.

Be sure that the pulley on the alternator is not too wide for the belt.

If the pulley is worn badly or is the wrong one, that could be the issue.

Rebuild facilities are terrible about installing the proper pulley's on things.

The practice with many is, if it fits, it goes on.

If the pulley is too wide and the belt bottoms out before the sides can "Bite" into and grip the belt, then the belt will slip and squeal.

I have never seen one that was anything like what you describe.

Bad alternator or pulley or a combination of all the above.

Wash the pulleys with brakeKleen to remove any oil or silicone.

Keep us posted.


Missy

[JohnC]

Also, if the pulley diameter is too small, it will be spinning faster than intended, adding to the belt load...

[atsengineering]

Also, if the pulley diameter is too small, it will be spinning faster than intended, adding to the belt load...
I had similar problem with my 6.2 motorhome the alternator pulley was rusty & the belt sat inside to low it broke like they where going out of fashion change pulley with a steel billet type no more problems P.s my motorhome has as a 100 amp alternator fitted.
hope this is helpfull