My 1985 300TD, with over 300,000 miles, makes strange noises when weather is cold. I should note that the entire car is in tip-top running condition....good compression, valve clearances always adjusted, recent top notch valve job, synthetic oil (rotella), new glow plugs, recent injectors, EGR valve disabled (ball bearing in rubber fitting), rebuilt vacuum pump..good vacuum, etc. etc.....but I'm wondering if the cold weather noises are possibly indicative of a problem.

The noises in question come from within the engine compartment just forward of the glove compartment....the noise happens only when the engine is cold, and is more pronounced when real cold (like this morning when temp. was -5F). It sounds like there is a manual gear box mounted right on the firewal where the mono valve is. At lower speeds (lower gear), the noise is more pronounced when I take my foot off the accelerator....sounds just like a loud manual gear box would sound if you were in first or second gear and you took your foot off the accelerator, allowing the engine to rev down while in gear. The noise definitely corresponds to engine RPMs....thus, I am assuming it is engine noise from the vicinity of the manifolds.

I dont recall when this noise started, for a while now. I may have become more pronounced after I cleaned all the gunk out of the exhaust manifold when I did the valve job (exhaust manifold more resonant??)

My question is this....is it just simply engine noise, and if so, why is it so pronounced when outside temps are so cold (I dont have a garage, so the car sits out in the cold all night). Does it have to do with the firing of the cylinders/combustion noises when cold?

Note: I also recently replaced all the coolant temp sensors and the like, but the noise still may be related to some sensor or vacuum related compensation device for cold starts. Anyone else have this experience, or know what is happening here??

Thanks,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

I never heard weird noises from my 300CD but it never had to go through such cold weather. My friend's 2000 BMW and 2003 MB even make weird noises due to this wonderful cold weather.

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2008 BMW 335i Coupe

On the way home from work tonight is payed very close attention to what happens. I think I know what the source of noise is....probably cold weather turbo noises. When I start the car, first start on cold morning or at night after work, the noise does not appear when in neutral (I'm assuming the turbo does not engage when in neutral???). But when I put it in drive, the noise is very pronounced. The noise appears at about 2,500 -3,000 rpms or higher. (is this about when turbo engages??) When I let off the accelerator, the engine quickly revs down to about 850 rpm (normal idle speed) but I still hear a very very pronounced rough gear-like noise...or a noisy spinning shaft....at high rpms noisily slowing down....seems that this is most likely from the turbo....i.e.the turbo rotor/shaft spinning and slowing down (???).


Once car is fully warmed up, noise goes away. In warm weather, no noise, car runs fine, turbo seems ok.

Is this cold weather turbo noise a symptom of a failing turbo. The car alway had regular oil changes, synthetic oil fo rthe last 175,000 miles. but the car does have over 300K on it, and the turbo is original.

Anyone have an opinion here? Am I now, or will I soon be in need of a new turbo??? What could explain this....do turbos in general hate very cold sub zero air??

Thanks

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

My 84 300D makes a strange noise when cold and accelerating at low rpm (around 1500-2000). Sounds somewhat like a small exhaust leak. Once warmed up or at higher rpm the sound is gone. Seems to come from the same general area you described but at different rpm.

When the temp gets below 30 degeees my car makes ALL kinds of never before heard noises, creaks, grunts, growls, grinds and etc..

I think it is just cold temp contraction and parts made of different materials contract and expand at different rates. Aside from that all else is solid and vibration free. So at this time I wil just turn up the radio and try to forget it!


thebern

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1982 240D 313,000 (4 speed)
1984 300CD 172,483
1985 German Shepherd Dog -Lacey- R.I.P.11/04/05

Hood Stars, Wrist Crowns and Obsession Dobs

MarkM,

My 83 300D with 251,000 miles exhibits the exact same noise that you describe in similar conditions. I cannot figure it out either but the car seems to be running fine.

Only problem I get is the fuel gelling in the feed line when traveling at highway speed in this extreme cold.