stange whistle sound - PeachParts Mercedes-Benz Forum

ajcbgray · #1 06-18-2008, 09:51 AM

I've got an odd whistle sound that has recently developed on my '85 300D. The sound is a whistling that is loud enough to hear (especially with the windows open) but is not extremely loud. It sounds like it is coming from the right side of the car and probably from the front, but its very hard to tell (it seems to come from the outside of the car, not through the cabin). The sound only happens in the 1.5-2.5k range on the tach and only under load. If its in park or neutral and I rev, I hear nothing. If I'm driving along hearing the sound and I slip it into neutral and coast the sound disappears. If I accelerate past 2.5k the sound disappears. If I let off the accelerator when its making the sound it dissapears. It doesn't seem to make the sound (or at least not as pronounced) in first gear.
My initial guess is that it could be the AT or the turbo... anybody want to take a wag at it?
ben

JCSC2 · #2 06-18-2008, 11:50 AM

Just wondering if your a/c is on with this whistle occurs?

ajcbgray · #3 06-18-2008, 01:10 PM

A/C is off

winmutt · #4 06-18-2008, 01:14 PM

Turbo. Screeching or whistling?

cbeaner007 · #5 06-18-2008, 02:03 PM

My '91 300D 2.5 had a very similar sounding noise. It persisted for about 2 weeks and then the bearing in the turbo seized. Needless to say the noise stopped rather abruptly after that. Majestic turbos in Waco, TX rebuilt the turbo and all is well now. Your noise may be different, but the circumstances around the noise sound very similar.

CW

ajcbgray · #6 06-18-2008, 02:24 PM

It's not screeching, just whistling.
Is there any way to test the turbo bearings for play and how hard are turbos to rebuild?

winmutt · #7 06-18-2008, 02:29 PM

If it is just whistling it is probably a leak in the intake manifold somewhere. It could also be your wastegate or wg hose. Since it goes away at a certain rpm this would be indicative of only whistling under boost until max pressure is achieved.

Gurkha · #8 06-18-2008, 02:38 PM

Check the water pump.

sethyboy85 · #9 06-18-2008, 03:39 PM

Quote:

Originally Posted by ajcbgray

It's not screeching, just whistling.
Is there any way to test the turbo bearings for play and how hard are turbos to rebuild?

if you get your fingers on your compressor wheel, from the intake side of the turbo... give it a gentle wiggle and report back if any up/down or in/out play is felt... the bearings "float" on oil so there should be less then 1/32" or so of play anything more and that could be a problem.

I would go with a leak after turbo in the intake system.

Simple test in parking lot, get some dish detergant and water, put them together and put some on the tubing (where it comes together) and watch for bubbles when you give the motor alittle rev. bubbles= leak.

Flyin4now · #10 06-19-2008, 10:49 AM

Does it occur right after an upshift? I had a horrible whistling/shreiking noise on my 85 300D. Turned out to be the Air Recirculation Valve by the turbo. Do a search on ARV or try to find previous posts by me. I put a BB into the vacuum line going to the ARV and the noise went away. Hope this helps.

MB-Owner-in-ind · #11 06-19-2008, 01:04 PM

Had whistling once and found my air cleaner mounts have failed and the u-tube fell off the turbo along with the air cleaner. Fixed air cleaner and sound went away.

winmutt · #12 06-19-2008, 02:59 PM

Maybe its time we met up for lunch and I can hear this whistle of yours.

turbobenz · #13 06-19-2008, 03:18 PM

Quote:

Originally Posted by JCSC2

Just wondering if your a/c is on with this whistle occurs?

whats this about an ac whistle?

2.5Turbo · #14 06-19-2008, 07:01 PM

Exhaust gasket leak? A while back on my 300D a couple nuts fell off the studs on the flange where the turbo connects to the exhaust manifold and the connection started to leak. There was still enough tension on the remaining studs to keep it from leaking when revved with no load, but when the engine was under load and the back pressure was higher, the leak opened up and sounded like a rat being strangled under the hood. Had a slight drop in power too; I would imagine the turbo wasn't producing as much boost as it normally would.

ajcbgray · #15 06-23-2008, 01:49 PM

Winmutt wins the prize! After a brief trip through Pull-a-part in the rain Saturday morning we took a short drive and tried to diagnose the whistle. He disconnected the EGR and the ARV and the whistle disappeared. I haven't had any time to figure out which one was causing the problem, but I'll repost with final results.
ben