Another weird noise in my 300SDL
 

I dunno, hate to seem paranoid but this is funny and not funny ha-ha. Almost sounds like a playing card in bicycle spokes.

https://youtu.be/Wte_EDFQgWE

I found this one from about a year ago to compare:

http://youtu.be/c21_xj4mesc

*ETA*

I'm wracking my brain to try to figure what, if anything, I might have lapsed on. I checked the oil when I first heard this sound, it was maybe 1/8 inch about the min, I'm about to change it. More important, I may have gotten slack a time or two about putting in enough lubricity additive. I'm running on HPR, the 2nd gen biodiesel that CA brings in, I gather one should use the lubricity additive. I've been using Howes Diesel Treat, one ounce to 5 gallons, usually more than that.

Maybe I'm tripping here, dunno. I'll put some extra in before I go anywhere, though I suspect if any damage has been done that horse has left the barn. I've seen no driveability issues in the last few days, power is good. Another odd bit, from the two vids it seems like the idle speed is higher now. My tach says about 700.

Tensioner shock or tensioner pulley worn out. They make that high frequency "chatter" when they crap themselves.

You mean this guy?

https://i.postimg.cc/9M7g451P/tensioner-lever.jpg

And this is the shock, I think:

https://i.postimg.cc/BQz01sBk/tensio...oner-shock.jpg

The dealer has the shock on the shelf - $93. Pelican aftermarket - $31. I was hoping to make a trip this weekend, might not work.

By the way, I’m liking your diagnosis doctor. Carefully taking note not to chop off my fingers with the spinning fan blade, I carefully touched my mechanics stethoscope to the lever body that holds the shocks and it sure sounds like that’s where the racket is coming from. No other parts that I touched give nearly as good a report. Looks like there’s two shock observers there.

Seems to me that a bad bearing in the pulley would be the source of the noise but you have more experience in this issue than I do, that much is clear.

Looks like I’ll need to take the radiator out to do this job. Once I get the parts.

Might as well replace the spring and pulley also - my spring broke about 5k miles after I replaced just the lever. Parts from Pelican, that was about 10-15k miles ago - so far so good.

Yeah, I’m thinking to replace it all. Hard to get in there, may as well do it right. I found a place here locally, not your normal chain auto parts store - Kohlweiss. They can get me the parts this afternoon, after market, but I think I’ll go that route here.

What I can’t figure, it looks like there are two shocks going on but he says only one is required. I’ll look closely when I get back.

You can do the job without removing the radiator. One of the shocks is the shock you linked, the other is a spring in a rubber tube. Release tension and rock that tensioner pivot back and forth. If it seems loose and sloppy, or if it feels tight and gritty, its needing replacement. If it's smooth, leave it alone.

Replace the shock and the spring as a pair. If the tensioner pivot needs replaced, you can do it without removing anything from the engine. It gets TIGHT against the fan, but you can do it. If the pulley on the tensioner needs replaced, now is the time.

Usually the tensioner parts are ok, it's just that shock that wears out and causes a heck of a racket. As mentioned above, the spring usually fails soon afterwards from stress, so it's a good idea to replace it preemptively.

You’ll need a 12mm hex bit for the tensioner arm bolt.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Good call, I think my biggest is a 10mm. I'm guessing it should be the L shaped variety rather than a socket. Might have 12 in a socket.

I wanted to change coolant today, taking the radiator out wouldn't be a huge problem. But I'll look it over.

The torque spec for the tensioner arm bolt is 50- or even 70 lbft so you need a socket rather than a key. Go easy on that bolt. MB added internal ribs in each of a handful of front cover redesigns.

Sixto
98 E320s sedan and wagon
02 C320 wagon

This must be the spring, eh?:

https://i.postimg.cc/9M7g451P/tensioner-lever.jpg

(I'm not Canadian, 'say what?' seemed a bit much)

The shock is an easy replacement. My existing shock had full resistance one way, but no practical resistance the other. The bushings that the bolts go through we’re stuck in tight, but spun almost as easily as if there were bearings. The new one had fully tight bushings.

It made a marked, substantial difference in noise and smoothness.

That is the "Belt Tensioner Lever for Tensioner Pulley". The belt tensioner spring connects to driver side of that lever and the belt tensioner shock connects to the other side.

This was a challenge. I undid the top bolt on the shock absorber but on the bottom, I got it unscrewed, tried to slide it forward, no can do. Will not come out, the pulley stops it. Nor can I pull the piece upward, the bolt is still inside it somewhat.

One option is to take the water pump pulley off but to do that I first need to take the fan clutch off. If it was my BMW E30 would have been off 15 minutes ago. It takes an 8mm allen socket just fine but which way to turn it is the question. Neither way wants to break free. My bimmer has reverse threads on the fan clutch, that way you don't even need to tighten it seriously as the clockwise direction of the motor will act to keep it snug. I sorta hate to bang it with hammer to break it free if I'm going the wrong way.

I was in trouble with the bolt on the bottom of the shock, couldn't screw it back in so I cut it off, easy enough to get another. While putting it together I'll practice with a doable method to swap the shock w/o pulling the radiator and fan. I read that the shock can have short lifetime.

I get the rest of the parts in the morning, was just prepping. I'm glad I got a new Belt Tensioner Lever. The old one has some slop in the movement.

Put an OAP pulley on the alternator and never have to worry about the tensioner again.