Screeching alternator

My 97 Nissan pick up, 2.4L I4, 5 speed 182k miles has developed a screeching sound for about 15 to 30 seconds after starting. It sounds like a loose or slipping belt. I have replaced all three belts and the tension is right.

I pulled all the belts again and put them back on one at a time and determined that the belt for the water pump and alternator is the source. I checked all pulleys and components and cannot find anything with abnormal drag or roughness or noise.

I though maybe that I might have put too much tension on the alternator belt and maybe put to much side load on the alternator bearing so I loosened it slightly and that just made the screeching last longer. I also noticed that the duration of the screeching is extended when there is a load on the alternator, such as the blower motor or the headlights.

Once the screeching stops, it does not come back even with sudden changes in rpm or changes in load, i.e. blower motor or headlights, however, every time the compressor kicks on, there is a chirp. Before I replaced all the belts, the compressor belt was slipping on occasion and every time the compressor kicked on, it would screech for a few seconds, but its not AC weather right now.

I pulled off the alternator today and took it up to be tested to see if it would screech on the test set, not a peep and passed all tests. BTW, I am not having any issues with charging or starting, the battery is good. I did notice a wire bundle that runs under the air cleaner has abraded and one wire is bare, I’ll address that tomorrow. I don’t see any evidence of shorts in the bundle, all the abrasion is on one side and only one wire exposed, and it only touched plastic as far as I can tell.

Also, I cannot visually detect the slipping, the belt and the alternator appear to be moving smoothly, same with water pump, but its hard to tell because everything is spinning so fast. also, it is not bad if you just do a restart after driving, is will only screech for a second or two, but if it cools down, than it back to the 15 to 30 seconds of screeching, and its LOUD.

Dead cell in the battery, putting a BIG load on the alternator right after start-up…Faulty voltage regulator over-loading the alternator for a few seconds until the voltage stabilizes…Worn pulley on alternator allowing belt to slip…Wrong belt, not wide enough for pulley…

The screeching alternator has bad bearings. Usually it just gets replaced. It should gradually get worse and happen randomly unless it breaks suddenly and burns the belts right off. A new alternator solves the problem right now. Why walk?

More useless info.

To check bearings, take the alternator apart and have a look. It’s easier to reasemble than you might think. Pinning the brushes with a drill bit is easy. You just push the brushes in and put the pin in the hole to hold them in. Put alternator together and pull the pin. Mark the cases because the thing can be put together with the case in the wrong position if it’s like GM ones. You will know this if the wires won’t reach to plug into the alternator. Then you take screws out and rotate it to the right spot. Too easy. If brushes are worn to a quarter of an inch, they’re gone too.

Alternator is not bad, the bearings in it are good so there is no need to replace it. It did not screech on the test set. It is a new belt but I will look into it being the wrong belt because even though it was doing this before with a belt that was about 10 years old, it did seem to get a little worse with the new belt. Worn pulley??? This truck uses V belts.

I’ll check the cells in the battery. It is only a year or two old but I’ve had batteries go that soon before, and some that lasted a long long time.


any chance the pulley grooves are slightly glazed?

Is there a possibility that one of the pulleys is ever so slightly misaligned?

You mentioned that it is not A/C weather. You know the A/C runs whenever the defroster is on, right.

Have you checked the width of the belts compared to the grooves they fit into? A belt that is the slightest bit too wide or too narrow can squeal like a pig.

With the engine off, you might consider putting a socket/ratchet on the alternator pulley nut and then try to rotate the pulley on the belt. The pulley should be very difficult to move.

Pulley grooves glazed, possible but I have never seen that before. I’ll take a little sandpaper to the alternator pulley while I have it out. Can’t hurt.

On this vehicle the defroster does not automatically turn on the AC, I tested that for another thread discussion we had here a while back. A lot of times, it is necessary to turn on the AC to effectively defog the windshield, but since I am retired now, I don’t drive much under those conditions. I put the new belts on last summer and for the rest of the summer, I didn’t have the screeching from the AC.

The belt appears to fit, but appearances can be deceiving. This problem has gotten a lot worse since I put the new belt on so that is a real possibility, but it didn’t start immediately after the belt replacement or I would have take the belt back and gotten another one. I’ll check that fit again.

Just an update, weather has been bad. Today I deglazed the pulleys with some 220 grit sandpaper. The belt is the right one, but last year when I bought the belts, they didn’t have the higher quality belt for the alternator so I got the cheap one. I got a Gates belt today.

I rotated the engine to line up the timing marks and then checked the rotor position in the distributor thinking the harmonic balancer might be the source of the noise, but it lined up. However the timing marks are on the innermost pulley and the alternator belt is on the middle one that is the weighted pulley, so I put paint marks on the timing marks and on the heavy center pulley. If they shift after I test it again, then I’ll know.

I have most of the front of the engine back together today, thanks to those engineers at Nissan for making a simple job as difficult as possible. I see why the lower radiator hose is a two piece hose, but unfortunately they have never been separated so after 15 years, they ain’t coming apart now.

Will finish up tomorrow after I check all the cells in the battery.

Got it back together today (after dental appointment) and no more screeching. I don’t know if it was the belt or sanding the pulleys, but I suspect that it was the belt. Moral, don’t buy a cheap belt even if it is the only thing they have in stock. Unless its an emergency of course.

Good deal.

Good on you Keith for fixing it up right. Yes, sometimes the least expensive solution turns out not to be. When I go to the parts store, I ask the parts guy what’s available from their parts vendors, usually they offer three choices, from cheaper to more expensive, and I choose the one priced in the middle. Good, better, best in other words, and I choose “better”. That seems to work for me in most cases like this.

I never do the cheapo line unless I was stranded and needed to get home and that was all they had for sale… I always do the expensive line for belts, hoses, or anything absolutely critical and sometimes the mid-grade for less critical things. I bet it was just the cheap belt all along. These things sometimes only last a couple months.

If you still end up having trouble with this I suspect the problem is with the idler pulley bearings. Replace that bearing as they do wear out and cause this kind of trouble.

For what it’s worth, I have never had a problem with Gates belts.

As we all know, Gates actually makes the factory belts for several manufacturers.

Benz used to have their belts supplied by Continental. Later they switched to Gates. My fellow mechanics quickly recognized that they were superior. Nothing wrong with the contis, but Gates made a better product. At least in that instance.

Gates and Dayco make a quality product sold under their label and under store labels and both manufacture sub- standard products sold under store labels. I insulted the VP of the McParts chain regarding the “rubber bands” he sold. It’s a funny story. But too long. And possibly out of bounds legally.

I’ve never had a bad belt of any brand before, but I don’t usually by the “value” priced model, I only did that time because at the time, it was the only belt in stock and I really didn’t think it would matter on a 15 year old truck. I guess even us old dogs can learn something new now and then.