Screaching from the turbo 300tdt - PeachParts Mercedes-Benz Forum

Gordo · #1 11-09-2008, 01:00 PM

I did a search and could not find anything quite like this.

The Problem:
My 1980 300td now with a engine from an 1983 300d (long story) has developed a sound that seems to be coming from the turbo. It is a terrible screeching noise. It happens when the engine is warm and under load at aprox. 2500RPM. The pitch varies with load. It sometimes starts as an intermittent chirp and then becomes constant. It is hard to tell if there is any loss of power.

What I Have Done So Far:
Yesterday I removed the turbo and replaced it with one I had on a parts motor that never had turbo problems. PITA. The car seemed to run fine with the "new" turbo until I drove home to the mountains. The sound had a slightly different tone to it, but is back at least as bad as before.

What could this be? I think it must have something to do with the turbo since it changes with load and seems to be coming right from that area... But, how could both turbos be doing the same thing? Could the turbo be starved for oil? Any help would be great. Thanks.

#2 11-09-2008, 01:07 PM

Probably the alternator, fan or water pump. With the engine off, spin the fan by hand and see if its hard, loose or wobbles. It should spin with some resistance.

Gordo · #3 11-09-2008, 01:16 PM

The fan and alternator seem ok. I know that sound since I have delt with it before. I think this is the turbo because the sound changes with a change in load (as the turbo spins faster). It is not as dependent on RPM as long as the RPMs are up 2500 or so.

#4 11-09-2008, 01:19 PM

Could be an exhaust leak pre or post turbo or an air leak on the pressurized side of the intake. Look for black streaks of carbon at joints. Did you replace the two big o-rings between the turbo and intake manifold?

Gordo · #5 11-09-2008, 01:31 PM

There is a little exhaust leak at the down tube. I don't think It would make such a terrible screaming sound. I did not replace the o-rings between the intake and the turbo, but I did inspect them. They where not cracked and seemed to fit tightly. I will take the air filter off and look for black streaks right now. Thanks for your help.

Gordo · #6 11-09-2008, 03:21 PM

Thanks Forced. I think you got it. There is a pretty bad leak between the exhaust manifold and the turbo. I tried to tighten the bolts to stop it, but the problem must be the gasket (I used the old one). I didn't think an exhaust leak could sound like this, but I bet that is the problem. I will post when I know conclusively and it is fixed.

#7 11-09-2008, 09:53 PM

Clean both mating surfaces very well. Carbon and rust will make the surfaces uneven and ruin new gaskets.

Chris W. · #8 11-10-2008, 12:29 PM

I'll just about guarantee that this noise is an exhaust leak. I had an '89 Mazda turbo which developed a chirping, shreaking noise. It was loose exhaust manifold bolts causing a leak. The character of the noise changed as the manifold warmed up and expanded.

Rgds,
Chris W.
'95 E300D, 275K