My turbo just got really loud - PeachParts Mercedes-Benz Forum

otto huber · #1 08-02-2016, 03:09 PM

The car is an '81 300SD. While driving the car yesterday I noticed that the turbo was a little louder than usual while driving around town, then when I hit the highway it was really loud, making me think that I might have an exhaust leak. I checked for a leak this morning and I can't fin anything near the turbo or upper exhaust pipe. There's a tiny hole in my muffler.

The engine still performs well with good acceleration and idle. The sound is loudest between 55 and 65MPH. I just changed the fuel filters this morning, and the car is also due for an oil change which I'll get to in the next day or two. The noise is a loud growl, not a whistling sound.

BillGrissom · #2 08-02-2016, 05:48 PM

Doesn't sound like a turbo problem. I expect that would be screechy sounds. When you start an engine cold, you can usually feel for puffing exhaust leaks at idle before things get too hot and burn your fingers. Tissue paper helps too (a Wheeler Dealers episode).

SD Blue · #3 08-02-2016, 06:56 PM

Usually, exhaust leaks are mentioned in the flex portion of the down pipe. Particularly when they are very noticeable in the cabin

otto huber · #4 08-04-2016, 10:44 PM

I removed the air cleaner today and checked for exhaust leaks, but couldn't find any. Next time I'll try lathering up the area with soapy water and search for bubbles. I also changed the oil and air filter. I can feel that the engine is working a little harder by the increased vibration in the gas pedal. I might try bypassing the turbo over boost protection valve.

dude99 · #5 08-04-2016, 11:16 PM

Define "louder" are we talking a whine, a howl, and squeal or some other noise???

otto huber · #6 08-05-2016, 12:02 AM

A growl, accompanied by vibration in the gas pedal.

While doing a search on this subject, I came across a post stating that a leak near the turbo will cause it to spool up faster. The car definitely throws your head back when the turbo kicks in, drives my girlfriend crazy.

patbob · #7 08-05-2016, 10:42 PM

Maybe blow smoke up the tailpipe?

Murkybenz · #8 08-06-2016, 05:18 AM

disconnect glow plug relay on a cold engine and look under hood as someone turns the key, engine cannot fire and will belch out grey smoke and any leak will be visible.
Vibration in gas pedal normally bad engine mounts ?.

otto huber · #9 08-14-2016, 10:42 PM

I've now tried three different methods to find this leak: soapy water all over the exhaust system while running, dragging tissue paper along the manifold, pipe and turbo, and having a buddy clog the tailpipes with a rag while I search the system. I thought that the clogged tailpipes would work for sure. A huge plume of black smoke came out of the tailpipes after the rags were removed, so you'd think that if there was an exhaust leak it's location would be obvious.
Also, the car runs much quieter and smoother at 75MPH than it does 65MPH, could this point to something other than an exhaust issue?

I'm ready to take the car to a shop, should I go to an exhaust place first or an MB mechanic who I know is familiar with these cars?

dude99 · #10 08-15-2016, 08:47 PM

I would use an MB mechanic first as this is sounding less and less like an exhaust issue to me.

patbob · #11 08-15-2016, 10:47 PM

Quote:

Originally Posted by otto huber

I've now tried three different methods to find this leak..

No offence, but none of your three methods sounds terribly likely to work. A diesel doesn't (shouldn't) generate much smoke at idle, or even revving the engine when not under load, and the other methods are only going to work if you can see the leak. Remember, you're looking for a leak that leaks a lot of air when everything is hot and under some exhaust pressure.

Like I said.. try blowing smoke up the tailpipe. You want thick, dense smoke so you can spot it before it dissipates. Run the engine up to temperature and then shut it down and hook a smoke generator to the tailpipe. You can try something like this Paint Can Smoke Generator.

I did something like that but using an aquarium pump for an air source when I was chasing intake air leaks on my Volvo. It should work pretty well for exhaust leaks too. Might want to use damp wood instead of a dirty rag through -- the smoke would probably smell better (I used a cigarette and there was a toxic smell from that intake for months -- I'm a non-smoker, so I found it particularly obnoxious). With smoke and a good powerful flashlight, I found my vacuum leak, even though it was behind a bunch of stuff -- just look for the smoke wafting around and follow it back to it's source.

Quote:

Also, the car runs much quieter and smoother at 75MPH than it does 65MPH, could this point to something other than an exhaust issue?

Most likely, you're hitting a resonant frequency, sort of like a bassoon, and missing it at 75 MPH due to different load and pulse frequency.

otto huber · #12 08-23-2016, 02:14 AM

I haven't had time to assemble a paint can smoker, but was thinking of pushing dry ice smoke through the tailpipe with a shop vac on blow setting. Would the dry ice smoke be dense enough?

The noise hasn't gotten any worse, but it's still annoying to have so much noise on the highway. I stopped by a reputable exhaust shop and the owner plugged the tailpipes with his hands and felt that there was too much pressure for there to be an exhaust leak. I'm not sure how much to value his opinion, but I thought that I should throw it out there.

Also, while taking a 40 mile trip on the highway the noise was constantly present and would change to a lower pitch when I took my foot off of the accelerator. The engine temp was normal. Is it possible that the lock nut on one of the exhaust valves has come loose and the engine isn't breathing properly? I adjusted the valves about 7K miles ago.

scottmcphee · #13 08-23-2016, 01:38 PM

go to a Vape shop if you want to generate smoke, it's all the rage.

..explain your need, they'll have something

Skippy · #14 08-23-2016, 08:19 PM

From reading this far, I don't think it's an exhaust leak. Unfortunately, I don't know what it is. Can the OP post a recording?

junqueyardjim · #15 08-23-2016, 08:44 PM

If it is the siren like whine of the turbo that suddenly increases it can be cause by the hoses and hose bushings in the air intake from the air cleaner to the turbo. They have to be properly installed and until you get it right it will increase the noise level. A sharp, I would call it a machine gun rattle is heard if the turbo wheel gets enough lateral from worn bearings to allow movement to hit the inner wall of the housing. You will definitely not like to drive it if it is doing that and at that point the turbo is junk.