stevespringer

Hi all,
I have a new (2000 mile) C240 with a strange engine knock at startup on a warm engine. Sounds like bearing and goes away in a couple of seconds. Took it to the dealer, who said they hadn't had an complaints. 3 service techs decended on the car and when started heard the same thing I had. An overnight visit yielded a phone call that according to the factory service rep, the noise is normal.

I asked if their other new C240's sounded like this on a warm engine...they said the heard the same noise on others.

Question...has anyone else out there heard this racket? Sounds like bearings to me! Perhap the thin oil is the problem. Still and all this kind of abuse is not good for journals and bearing if that is what I'm hearing. Comments?

MarkL

Yes Steve, I've noticed it too. I posted this question a couple of times but no one else really had the same thing. Since it never happens on a really cold start, I've assumed it's nothing important. If yours is like mine, it usually happens after it's been off for let's say 30 minutes even up to a couple of hours. When you start you hear what I would describe as a "deep" knock (not like a valve noise - something much "heavier") that occurs for 3-4 times and quickly subsides. I've had my car since August and have about 4800 miles. Like I said, I've assumed that if it's really a lube problem it would surely occur from a cold start. Even if my car sits idle for 2 days in cold weather, I've never heard the noise at initial start up. I'm glad someone actually talked to the dealer about it. I've even wondered if it could be some engine accessory noise, like an air pump or something.

BTW, I knew a Steve Springer years ago. Did you ever live in the Silver Spring or Wheaton areas in Maryland?

stevespringer

Yes, I use to live in MD. Actually in Howard Co. near Lisbon. Worked at JHU/APL and Motorola

MarkL

Must be a coincidence about the Steve's! This guy went to Northwood HS in the early '70's I'm pretty sure, and was engaged to my cousin! Things changed and they parted ways.

Anyway, does the sound I'm describing seem the same as yours? I'd really like to know what they say the noise is. Also, the overnight stay probably wouldn't help since it doesn't happen cold. I've also discounted the noise since it's a Mercedes (!) and nothing should be wrong, right? BTW, is yours a 6-spd like mine? Someone had noted in the earlier post that the 240 and 320 engines are based on the same block, etc., so I'm wondering why none of the C320 owners have noted this.

stevespringer

Must be another Steve Springer... Your knock sounds just like mind. Nothing on a cold engine. Engine seems to need to sit idle for 15 - 30 mins for the oil to drain down before I notice it. The only difference between 240 and 320 is a longer stroke...blocks are the same. Incidently mine is a automatic.

The dealer didn't have any explaination for the noise at all. Now that I have a record of taking it in for service for the problem, if it flies apart at least I'll have some documentation. I will ask for a heavier weight oil when it goes in for service at 10k miles. Perhaps that will be the remedy. Thanks for replying... at least it not my imagination.

Fuzzo

Could this be the noise of the purge valve? I know some people on the board on edmunds i believe told me that they had the pruge valve replaced for this knocking noise? is this what you may be referring to? I will go back and check edmunds to see if I can find the part number for the new part.

stevespringer

Fuzzo..
I learned about the purge valve problem when I took the car in for the startup knock. I had heard this persistent soft knock, but it was unrelated to engine speed, so I dismissed it as something else. The service guys mentioned that a new bracket was available to isolate the valve from the chassis. It was replaced and fixed the problem. Still have other knock however. Thanks for the reply!

Fuzzo

I haven't heard this problem but honestly I have probably wouldn't be able to hear it even if it was there because my windows are up. I'll try to keep an ear out for this noise.

Please let us know if you find a fix ....

MarkL

Fuzzo, it's probably actually easier to hear the noise with the windows closed. The sound seems to be coming from "deep" in the engine so it is easily heard through the firewall. BTW, it doesn't occur with every warm start -- is this true for yours as well Steve? It only lasts a couple of seconds and seems to be a series of about 4 "knocks".

Not sure there's really anything to "fix"... Remember, some people don't even hear their seatbelt warning beeps when they start up!

BrabusCClass

Ive never heard a noise from my car like that.

David N.

I've haven't noticed anything myself. I'll keep my ears open. If I hear anything I'll let you guys know.

Take care guys.

stevespringer

Mark,
I don't hear the knock on a warm engine if it is restarted within a couple of minutes of shutdown, but always hear it after 10-15 minutes or so. Your desciption is right on...deep in the engine and disappears within a second or two. I certainly hope it nothing serious; the last thing I need is to have an engine rebuilt with only 2200 miles on the vehicle, especially in a car of this class.

Mike T.

Whatever is causing the noise, it is something that relies on oil pressure to prevent metal-to-metal contact. That basically means valve gear and engine bearings. The service guy that dismissed the noise is trying to avoid expensive warranty work, nothing more. The mere fact that some cars do not make this noise indicates that something is amiss with yours.

Now for some speculation: It could well be a wrist pin that's just got slightly too much play in it. I used to have an old Peugeot 404 that did this, but also when cold...other times it would not do it. Rather peculiar really. The car had 125,000 miles on it when I first noticed the noise. It consisted of three or four loud metallic knocks which went away once the oil pressure built up... that engine is still going strong today (in someone else's car) and the noise is no worse than it was 16 years ago. Wrist pins almost never let go like big end bearings do, so a catastrophic engine failure is highly unlikely due to a noisy wrist pin. If you're unlucky, it may get louder and remain audible when oil pressure is up, at which time the engine should be rebuilt.

You should tell the dealer and M-B service rep that you will not accept what may be a long-term reliability problem on your car and that you would accept a new or standard exchange engine (rebuilding the existing one may not make the noise go away, unless they change literally everything).

If, on the other hand, these individuals can demonstrate to you that every Mercedes engine does this, well, don't worry too much about it. They would demonstrate this to you by supplying a detailed, highly technical, written explanation from Mercedes-Benz service personnel as to what exactly is causing this noise and why it is nothing to worry about. They'll never write such a letter, so you'll have to go for the full meal deal I guess.

Good luck.