C250 CDI 2012 mettalic rattle at cold start

[Tonygw]

Hi Guys

I own a 2012 C250 CDI AMG blue efficiency with 87K miles on the clock. It has a nearly full MB history with nly 1 independnt service.. Services done once a year.

At cold start if I jump in the car and crank the enigne it starts first thing but with a horrible mettalic ticking rattle sound for no more than 5 seconds then its smooth (diesel engine smooth)

If I turn the ignition key, wait for the glw plug light and then wait for the fuel guage to display its fuel level, and then crank the engine, it appears the rattle does not happen. I need to check this a few more times though.

Does this sound like a problem with the car? Or should I always wait a few seconds before cranking the enigne for the elctical systems to start?

Or is there something more sinsiter happening here?

Any help appreciated.
Thanks

 

[clk320x]

Does this sound like a problem with the car? Or should I always wait a few seconds before cranking the enigne for the elctical systems to start?

Problem with car

These OM651s are known for failing timing chains which rattle on start. That would be my guess.

Good news is the cost to replace should be sub £1000 at an indie with OE parts.

 

[Smart320]

Problem with car

These OM651s are known for failing timing chains which rattle on start.

Good news is the cost to replace should be sub £1000 at an indie with OE parts.

As long as it is done before the Big Bang!

 

[clk320x]

As long as it is done before the Big Bang!

They don’t tend to cause sudden engine destruction AFAIK, mainly just rattle! which gives you a chance to get it fixed haha

 

[Tonygw]

Thanks guys

How I can check if thats the real problem? Is there anything I can do to diagnose it?
Is it just the chain that stretches or does it need more work?

I'm quite worried now as its my daily driver.
I bought the car as I thought the chains in these were set to last the life of the car??? Is that not the case.
Thanks

 

[clk320x]

I'm quite worried now as its my daily driver.
I bought the car as I thought the chains in these were set to last the life of the car??? Is that not the case.

They are meant to but the OM651 had problems with the timing chain.

 

[steveq]

If I turn the ignition key, wait for the glw plug light and then wait for the fuel guage to display its fuel level, and then crank the engine, it appears the rattle does not happen. I need to check this a few more times though.

If that proves to be true, it sounds like it is more to do with the glow plugs not having a chance to heat sufficiently to help the ignition of the diesel.
You should always let the glow plug coil light on the dash go out before trying to start a diesel -- it is only a couple of seconds delay anyway.

 

[Tonygw]

Yeah thats whats got me confused. When I turn the ignition key to position 2 I can hear some kind of mechnical noises from the engine, and the glow plug light goes out, a few more seconds and I start it up, most times so far it hasnt rattled at all. I'm going to try another cold start soon as am going home from work and its been sat all day. So will try it and wait a few seconds util the glow plug light is out and see what happens , fingers crossed .. no rattle...

 

[MercedesDriver]

I always wait for the glow plug light to turns off, radio to turns on the screen then I start it up and it always start smooth.

 

[Deletedmember130310]

Will waiting for the glow light to go out ensure the oil pump is primed and ready to feed the tensioner?

 

[clk320x]

Regardless of whether you wait for the glow-plug light to go out or not there should NOT be any rattling.

The weather is too warm to even need glow plugs at all at the moment anyway.

You need to have the car looked at by MB/indie.

 

[MercedesDriver]

Will waiting for the glow light to go out ensure the oil pump is primed and ready to feed the tensioner?

As I understand it some oil spray nozzles in CDI engines are electronically operated and get switched on at the engine pre-start so I would say that some lubrication is necessary to be done before crank, not only heating the combustion chamber.

 

[steveq]

As far as I know, the only action when the key is turned to position 2 is that the fuel pump starts in order to build up pressure.

Maybe that is the mechanical nose you are hearing?

It is a barely noticeable hum/buzz on my car.

 

[Tonygw]

OK quick update. Had the oil changed for some petronas 5W30 merc spec and a Mann oil filter at my local independendent today.

After the change he could not notice any rattling when started immediately after the oil change.

He also left it a couple of hours and started it but could not hear any rattling at start up.

I'm going to drop it off at our Local Mercedes specialist today for them to try a cold start in the morning and let them have a listen to see if they hear it?

Could it be the oil was the culprit? I dont know what oil or filter was used last time but it was apparently changed at 80K miles and is now just a tad under 88K. The internet is awash with stories of chains failing and chains lasting 300K with no issues. Is it really a lottery??

 

[cws196]

No, it’s not a lottery. Yes, early OM651 engines did have chain issues but MB quickly resolved the issues. The internet is awash with <the same few> stories mainly from around the same time. Also consider just how many OM651 engines are out there and if there were issues then we’d be hearing a lot more.

 

[Marcbennett]

Have you managed to resolve the rattle? As people have suggested it to be the chain, that is the right path but I’d try a new chain tensioner before anything. I’ve had a fair few rattles on 651 engines, I’ve changed tensioners and job done. If problem is still there you can get the slack measured for peace of mind


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[Tonygw]

cheers for the reply. so the latest on this is, after the oil change it seems to be fine, no rattle, but a few days later I heard it one morning. Same again after work after the car had been sitting for 8 hours. The next day nothing, quiet..
But then a day later it was back. It seems like its a bit intermittent.
Which is a tad annoying lol.
Anyway its booked in to our local MB specialist on Friday. Going to leave it with them thursday night so they can do a cold start in the monring. But I'm thinking that if they dont hear the noise I might just bite the bullet and get them to carry out a chain replacement etc

I was wondering if it might just be the tensioner which is a much cheaper option. Do you think its worth doing just that or is it not delaying the inevitable? I would love for it just to be the tensioner but wouldnt want to find out 6 months later I still need a full chain replacement.

In your experience has the tensioner been a long term fix? My car is coming up to 90K miles with mostly full merc history but the oil change intervals have all been 15-17K which worries me. I prefer a 6-8K oil change on my cars. could this affect chain life?
cheers

 

[Marcbennett]

Yes I’ve had this issue on a few before, I work for Mercedes commercial main dealer and work on 651 engine all the time. I’ve been there 5 years and never seen a chain fail, I’ve seen chain guides fail and cause rattles but that’s an engine out job to replace the guides.
I’ve always replaced tensioner first as Mercedes claims the chain should last the life of the vehicle [emoji848]. Not had one come back with a rattle.

If they come to the conclusion to replace the chain, the engine doesn’t need to come out. You can change the chain in situ.

Mercedes always have long service intervals so I wouldn’t worry too much about the long services.
I always change my oil and filter once a year just so it’s always fresh.


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[Tonygw]

Thanks for that, it gives me some hope lol...I'll see what they say on Friday but if it's just the tensioner I'll be very happy. You've given me some hope

 

[Marcbennett]

I’m glad I can help, I’ll be very interested to hear what they say about it. The 651 is a really good strong engine.

Good luck


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