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  #1  
Old 09-14-2002, 07:17 PM
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V-6 Start-up Knocking

My 2001 C-320's engine has produced a knock-knock-knock-knock (presumably until oil pressure comes up) on 90% of it's engine starts since it was new. Hot or cold, makes no difference. This is the same sound one hears during the first start after an oil change until pressure comes up. My '95 C280 did this (it had an oil pressure gauge, unlike the C320) so I know that it quieted down as soon as pressure was seen on the gauge and was not heard again until the next oil change.

Looking at the microfiche, I see that the V-6 has a check valve at the oil pump outflow and I'm theorizing that the valve is sticking open so that the pump loses it's prime on most shutdowns.

The question is, is this a rod knock and does it in fact do any damage, anyway? BTW, oil used was the factory-fill Mobil 1 0W40 which is now Mobil1 15-50 since 0W40 is not available at retail yet. When it is (and I don't mean at dealer prices) I will be switching to it.

Roger Ellingson/Seattle
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  #2  
Old 09-14-2002, 07:25 PM
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The early V8's on the first model year of the full-size Toyota Tundra have a similar knocking noise, and it was determined by the factory to be piston slap. It disappears once the engine warms up. I wonder if it's the same for your car.

By the way, Toyota says the piston slap is harmless and is not replacing or fixing engines that are affected.
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  #3  
Old 09-14-2002, 07:34 PM
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V-6 KNOCKING

Thanks for the reply. However, as I stated, the sound occurs whether the engine is hot or cold. Further, it only lasts a few seconds or about four crankshaft revolutions (four knocks) until pressure comes up. It is also not a lifter whichwould make a clicking sound.
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  #4  
Old 09-14-2002, 08:00 PM
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Well, you're right, it kinda sounds like an oil pressure problem on start-up, or at least an oil circulation issue.

I hope someone can help you with some advice on this here on the forum...
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  #5  
Old 09-15-2002, 03:01 AM
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Roger.....

...go to member "JimF' website. He has listed a number of various issues dealing with MB cars. If you look under issue #18 he describes a situation similar to what you describe. He also lists a solution to the problem.

My W126 420SEL makes a similar sound. It happens mostly when it is cold and it doesn't happen all the time.

Hope this helps you.

http://pages.prodigy.net/jforgione/MB_S500.html

Good luck.

PS: By the way, if your car is running hot, check out Jim's "cool harness." My daughter's 300TE was running hotter than I liked. I lower the coolant to water ratio to 45/55, added WaterWetter and installed a cool harness. Her 300TE has been running cool and smooth, even in the recent 100+ degree heat wave. check it out.
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Last edited by BENZ-LGB; 09-15-2002 at 03:25 AM.
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  #6  
Old 09-16-2002, 12:24 AM
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V-6 engine noise

JimF's post #18 is talking about lifter noise which is definitely not my car's problem. It's knock-knock, not click-click.
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  #7  
Old 09-16-2002, 12:47 AM
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JimF's post #18 also pertains to the 119 engine, not the 112/113 engine, totally different motors.

Gilly
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  #8  
Old 09-16-2002, 01:04 AM
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V-6 STARTUP NOISES

Dan,

Yes, I also noticed that the engine type on JimF's website didn't match my question. So, going back to my first post, is this a rod knock I'm hearing and does it do any harm? Could that checkvalve be stuck open? Not being able to see a diagram of the oiling system, where does the oil from the pump go to first? I did hear two lifter clicks on first startup for the day yesterday which is the first time in 11000 miles. When my car finally goes in for the B service, Mobil 1 0W40 will be used, not the Mobil 1 15/50 I'm using now. Which won't change anything because that was the original oil (0W40)which was replaced at 4000 miles when the oil level sensor was changed and the thing was knocking previously.

Roger Ellingson/Seattle/Still the best MB I've owned out of six.
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  #9  
Old 09-16-2002, 07:40 AM
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You're asking me to diagnose a noise your engine is making without hearing the noise. What's wrong with this picture?

Gilly
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  #10  
Old 09-16-2002, 01:36 PM
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LOL. 112's are noisy on start. 113's dont seem as noisy. As long as the balancer (which will NOT knock) I've not seem a 112 come apart for knocking.



Joe
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  #11  
Old 09-16-2002, 01:37 PM
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ROGER E,

I have a 1998 E320 (v-6) with the same symptoms; 3-4 knocks at start up, hoy or cold. Mine did not occur when the a/c was OFF.

My brother-in-law is a MBZ mechanic and diagnosed it as the a/c compressor clutch. He said they all do this right after start-up to "check" the condition of the compressor (in case they're locked up) to prevent further damage.

So, have yours properly diagnosed first to rule out anything serious. Mine is simply annoying for now, When it completely fails I'll get it changed.

Intruder
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  #12  
Old 09-16-2002, 05:53 PM
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Well, I agree with Gilly, it's difficualt to diagnose sounds via e-mail, but there are a few things to think about:

1. Knocking, as it detonation, is handled by the "knock sensors" that your car is equipped with. It automatically retards the timing to get rid of the knock. If detonation is indeed your problem, you'll need to try higher/different octane gasoline. Our 190E 2.6 HATES a certain brand of gasoline, and I found out it's high in sulfer and they often "fudge" octane ratings.

2. Oil pressure problems are unlikely, but could be really troublesome in the long run if that is indeed your problem.
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  #13  
Old 09-16-2002, 08:42 PM
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V-6 startup knocks

What's wrong with this picture?

Nothing at all. I described very clearly what this sound compares to in my first post:

"My 2001 C-320's engine has produced a knock-knock-knock-knock (presumably until oil pressure comes up) on 90% of it's engine starts since it was new. Hot or cold, makes no difference. This is the same sound one hears during the first start after an oil change until pressure comes up. My '95 C280 did this (it had an oil pressure gauge, unlike the C320) so I know that it quieted down as soon as pressure was seen on the gauge and was not heard again until the next oil change."

Seems to me that anyone who has been doing his own oil changes would be familiar with this sound. I certainly am and I'm not even in the business. And the suggestion that it might be detonation:

<<1. Knocking, as it detonation, is handled by the "knock sensors" that your car is equipped with. It automatically retards the timing to get rid of the knock. If detonation is indeed your problem, you'll need to try higher/different octane gasoline. Our 190E 2.6 HATES a certain brand of gasoline, and I found out it's high in sulfer and they often "fudge" octane ratings.>>

I know the difference between pinging and knocking and it's considerable.

The suggestion that it might be the AC clutch might lead me onto the right path except that these compressors have no AC clutch since they are swashplate compressors and are turning all the time even with AC off. But, since I'm getting nowhere here, I'm going to turn the HVAC system completely off for the next ten starts or so to rule out something in the compressor.
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  #14  
Old 09-16-2002, 09:26 PM
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Diagnosis

Hi,

Tough to diagnos a written sound but thinking about it, upon hot or cold start would not think it would have anything to do with something loose (piston slap) and metal heating up expanding and then quieting down.

Sometimes it's tough to dicern valve gear noise (I call rapping) from knocking. Sounds as though what you are describing could be oil preasure related as temperature seems to have nothing to do with it.

I do notice on my car that I get some valve train noise upon start up when I am down a little on oil. Keeping full tends to keep noise away at start up.

Would be easier to guess if it happened when cold.

Sorry can't be of more help,
Good luck,
Joel
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  #15  
Old 09-16-2002, 09:29 PM
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I also agree with Gilly , it is hard to diagnose a noise e-mail wise. Best thing to do is take it to a qualified and experienced technician if it bothers you that much . Last thing you wanna do is have an internal problem. Good luck
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