602 Engine Squeak (with video)
 

I'm having a hard time isolating an engine squeak on a 1989 190D with 149k kms / 95k miles. It is the high pitched sound you can hear in this video. https://m.youtube.com/watch?v=CzXPx5Z4iPQ

To my ears, I thought it was a failing bearing on the belt drive. It is more noticeable when the weather is colder, and more noticeable for first 10 minutes. However, it is generally pretty bad - you can hear it going down the street.

I moved the camera around for the video, which is representative of what I can hear :

- It is louder on passenger side than driver side
- It seems to be coming from the front, loudest when you are right over top of the head.

I replaced a couple of parts that we old anyway, just to try to fix:
- New alternator - old bearings had made some noise, but not terrible, and was smooth
- New waterpump - old one felt a little lumpy when turning
- New fan clutch
- New hydraulic shock on the belt tensioner (old one was leaking)

Also, the AC compressor is recent.

Any other thoughts about what this could be, or ways to diagnose? I'm somewhat stumped.

Sounds like belt noise to me. Tried a new belt? Tensioner pulley?

I haven't tried a new belt but I could - I have a spare.

Tensioner pulley was replaced 6years ago and 45k miles - I believe I spun it to heck but could double check

How was the pulley? Was it smooth and creamy, or did it spin freely? If it freewheels, even if smooth, it needs replaced and can make noise due to lack of lubrication.

I'd try a new belt, if the belt is old they can squeak.
I had a '95 F-250 with the 7.3 Powerstroke that did that, swapped belts and it stopped immediately. Never did it again

The pulley tends to wear to a conical shape, which makes the belt slip.

If you've never done it, it's a good idea to change the tensioner and pulley from time to time.

An easy way to check the belt: Put water on the belt while the engine is idling. If the noise goes away, you have a bad belt.

Thanks all! I went back in my records and found I changed the tensioner and belt, but not the pulley at 90k kms! Have ordered a new pulley and belt, will let you know if it works.

Sounds just like my 87 300d with an old belt and pulley.

Yes!!
This is how I isolated it to the belt on my old 7.3. OP should give it a try.

Worked like a charm. I replaced the belt and idler and squeak is done - engine sounds much quieter. Thanks to all for your help.