Turbo Screeching sound!!
 

Hi folks,

I haven't found any threads directly related to this problem,

1985 300td CA version,

When the engine is warm, hitting boost (going up a hill or accelerating) there is a gradually worse screeching noise coming from the engine. It genuinely sounds like the turbo is eating itself. The turbo has a gold compressor nut, and has zero shaft play that I can tell, I have not rebuilt it.

Some have said that this is an exhaust leak on one of the gaskets?? Any input from people with previous experience on this problem would be great-

Thanks

Check your drive belt tension and condition first. Most common cause of "screeching" in engine compartment when under load.

If after your investigation you still think it is the turbo.

The exhaust gass pressure pushes the turbine wheel towards the compressor side and due to that the thrust washer area on the compressor side causes the Compressor Wheel to get closer and colser to the Compressor Housing.
If the thurst washer area is worn enough the Compressor Wheel can rub on the Compressor Housing and make a screeching noise due to the metal to metal contact.

If that happend you can some times look down inside at the Compressor Wheel and see if the fins on the wheel show any wear of mushing over dur to the rubbing.

The other way to check is to remove the Exhast piping to get at the Turbine Wheel and manually push the Turbine Wheel towards the compressor end while rotating it. If it is making contact you should feel or hear some rubbing.

If your tubocharger system has some sort of rubber seals or hoses on it on the compressor side on to the manifold you when you are gettring boost you could be hearing an air leak.

Mix dawn dish soap and water so as to make a bubble mix (like kids use to blow bubbles) and spray that on a cold engine in the areas you think you have a leak. Start the engine and rev it to get post pressure. If you have an air leak you will see bubbles.

You need to check that before the engine ges hot.

A turbo shaft should have some side-side play when cold and not running and moved by hand. You should be able to rotate the turbine with toothpick pressure. If it's tight to rotate or has no play, then collision of sorts may have occurred with the shaft, and it's probably going to need an overhaul. Mine is tighter than I'd like but still easily makes full boost with quick onset.. Set to 1 bar with manual boost controller. So I'm leaving it alone.

I think it's unusual for a turbo to squeal like that though, unless its completely failed in which case the car would be driving like a dog.

Try spritzing water from a misting bottle onto the accessory belts while running and go for spin see if noise pitch changes or goes away.

Ok, thank you all for your input. I will look into the belts and further into the compressor side tomorrow.

I should also add that there is a distinct oil smell that comes up at the time of screeching (usually 2700 rpm+). I'm am thinking of starting with an exhaust gasket replacement kit, but will do more testing of above first.

I had a turbo screeching sound at higher RPM from my '85 California 300SD and it was the ARV. I had a bit of power loss associated as well, but IIRC a BB fixed that.

The trap ox thing that always cause the dilemma--that they recalled them for.
Usually what happened is the crap from the T/O came out and the little pebbles wear a hole in the hot side of the turbo--but its almost plainly obvious--the hole wears thru right in plain site on the top side of the turbine housing in plain view.--yours could maybe be in a hidden area--or it could be something else.

The Good news is, the regular 81-85 airresearch 49 state ones are perhaps the most reliable turbo ever bolted onto an automobile--EVER. and even more good news is they actually swap right in place of the odd 85 Cali one,
just get a working one from any other car and swap it out. the 84 and 84 ones have the dashpot thing on the compressor housing if you have to run the vacuum lines to it for the inspection goonz.

same issue....
 

I had the same issue with my '85 300D (CA version). The cause, if I remember correctly, was that the screws securing the manifold had worked their way loose over time. Tightening the screws made the sound stop without the necessity of replacing the gasket. I will check the invoice later when I am at the house and confirm by editing this post. Hope this helps...

EDIT: The invoice says, "Customer says check screeching sound at 2500-2700 RPM. Found intake/exhaust manifolds loose on cylinder head and missing hardware. Replaced missing hardware and tightened other fasteners. Checks okay." FWIW, I was billed 0.75 hours for the job at an indy. I do not see a charge on the invoice for the "missing hardware" they replaced.

This is so true,I've seen a few dozen of these turbos in junk yards and I've only seen one or two that was worn out and in need of rebuild. It's common to see original ones with over 300k miles still feel tight as can be. Pretty amazing

OK so update, I cannot tell if there are any exhaust leaks present, I will be diving deeper into that this weekend.

I plugged the ARV and egr, sound still there. Plus, if feels sluggish and does not accelerate well.

I forgot to add that the turbo had been making a slight screeching noise on deceleration at high rpms and temperatures starting about 6 months ago, but only on decelerations. Now this morning under full throttle the sound is there during acceleration, and deceleration.

Maybe pieces of the Trap Cat have broken off and plugged up the turbo/degraded the turbo over recent time...

This is really starting to worry me. Luckily I have the other turbo sedan finished, might have to use it for transport this week while I teardown the wagon...

Seems like its one thing after another with these cars lately

there is a technical service bulletin (tsb) about this issue on the models with the arv.

the solution was to drill a hole somewhere on the valve or compressor housing (i completely forget honestly) plugging the arv does nothing for this.

it was a common enough complaint that MB did something about it.


Unless you find another source for the noise, it is not an issue.

Try driving the car around in good weather without any attachments ( eg. air filter plumbing) on the compressor housing / turbo inlet.

How does the sound change? Can you repeat it in park or neutral?

Ok after more testing-

Without any air filter attachments the sound is more pronounced, and only under load. It is definitely something with the turbo because it is screeching from 2700-4000 rpm right after I start hearing the turbo spool up. I also cannot feel the usual turbo acceleration, the car's acceleration is sorta flat.

Disconnecting arv and egr does not affect the sound at all.

I am planning to pull turbo soon....:(

Just to update this and close the loop, the turbo needed to be rebuilt. Both the impeller and the bearings inside the turbo were worn. I rebuilt the turbo and it performed perfectly for a 1700 mi trip the next day. ��

2 thumbs up and another 2 thumbs up for coming back and telling us what fixed the issue.