mongo6407

Thanks for the youtube clips. No, the sound I am talking about is different. If I go up a hill, which in my town are many, the engine sounds like an aircooled VW Beetle from the 1960s. The dealer suggests I take the car to an upholsterer to have more sound insulation added, which is not recommended by MBUSA. I suggest the dealer fix the engine or give me the VW Beetle that goes with this motor!

mongo6407

Funny you mention the timing chain. I mentioned this to the dealer and I was met with scorn as if I had no justification to use my own knowledge to solve this problem. At some times the rattle does sound like a chain because it is a repetitive pinging during acceleration. Also, since engine knock tends to happen when the engine is hotter, I noticed that the sounds happen at all operating temperatures leading me to conclude the problem is not gasoline or engine knock related anymore.

Acapulco Bill

Yes the good old "dragging chains" sound, having owned many old (1961 to 1988) Beetles and also many VW microvans famous for this symphony of clatter.

Agree with the venerable Glyn M Ruck that the timing chain and tensioners could be suspect, sounds like the whole valve train is out of time on high torque application (i.e. uphill acceleration where the enriched fuel mix requires advanced combustion and causes the intake valves to slam against their seats in the last four-thousandths of travel).

RLE

Really. None of my air-cooled VWs had timing chains.

Acapulco Bill

@RLE: hahaha of COURSE NOT. Didnt even have lifters of course, just rocker arms that had to be set (was it 0.008"?) hence the looseness of the intake valve closure causing the "dragging chain" SOUND on acceleration, not that the valve train in the air cooled VW 1.2, 1.5 and 1.6L engines EVER had a chain in them. You are joking I hope!

Cosworth2000

Hello my friend,

Some good advice...MB is not my first car with the power I have as I had a RS500 Cosworth in my past.

If you ever put in lower octane in your car then what it design specifics and you get a bad response. Once you have used up enough to put a quarter of higher octane fuel in your tank....you should be good.

Hope this helps.

keith100

"Didnt even have lifters of course"

Got to have lifters, either in the crankcase or the base of the barrels. Not hydraulic lifters, but solid lifters. Which is why you had to adjust the valve lash.

Acapulco Bill

@keith100: Yes, of course no hydraulic lifters in the VW, and I remember I used 0.006" as the gap. But this is off point, the discussion here is to resolve the problem with the unusual noise upon acceleration. So here it is:

If on acceleration the engine sounds like it has MARBLES rattling around inside it, then its the OCTANE, get 91 octane and Costco has about the best, I use it in my V12.

However, if the sound on acceleration is like DRAGGING CHAINS which is a high-velocity tinkling noise with sort of a scrape to it, and to describe it exactly is like accelerating in an air-cooled VW (its an unmistakable sound), then valve-timing, the chain and the chain advance could be the problem.

Glyn M Ruck

This darn dealer needs to have an open mind when it comes to diagnosis. While I agree that it could be any one of a number of issues I had a W202 that had an engine rattle new. They first replaced the chain, guides & tensioner ~ that did not fix it. They the did a standard deburring procedure on the one cam adjuster ~ problem solved only to return. They then replaced the cam adjuster & I never had another issue in the time I owned the car.

Glyn M Ruck

I also believe we need to get the issue of possible trace knock being an issue here. I usually don't recommend these sort of products but this time it might help with the diagnosis. Fill up the car with the highest octane pump gas in your state & add Torco Accelerator octane booster to the tank. Tell us if it kills the noise you are hearing.

People with Nissan GT-R's on the forum that track them have had some success with Torco where they can't get high octane fuel that the GT-R really needs.

RLE

The earlier VWs had a fiber timing gear (not a chain) which eventually failed.

Thinking back into antiquity, weren't those called cam followers which the pushrods were socketed into? Wait, that's not the right term...

Same arrangements as my Porsche 356B Super, SC and 912.

keith100

Thinking back into antiquity, weren't those called cam followers which the pushrods were socketed into? Wait, that's not the right term.

Sometimes called tappets, because, well, that's what they did - tapped the pushrods "up" to actuate the rocker arm.

Glyn M Ruck

They were called cam followers!

Acapulco Bill

Why I refrained from mentioning "lifters" in an air-cooled VW engine!!!

mongo6407

I have been filling up religiously at Costco with 91 since my favorable experience in October, but now that the sound has returned I'm becoming less convinced octane has anything to do with the sound.

Question: Would the timing chain/tensioner/cam adjuster problem cause an intermittent sound? For example, I drove 15 miles to work up and down hill and on the highway one day this week and did not hear the noise. I traveled the same route home in the evening and the sound was prevalent.

Glyn M Ruck

Cam chain & adjusters I would expect to make the most noise at cold startup after a long stand & before full oil pressure is achieved.

Whereas knock can be ambient condition sensitive like a change in air density or driving under trees in an oxygen rich environment.

mongo6407

OK, I ordered Torco octane booster that was recommended in this thread. By the time I get it I will probably need to fill up again and report back to the group with my findings. By the way, the can I ordered is 32 oz. My tank is about 16 gallons. The max octane at the pump I can get is 91. How much Torco should I add if I fill the whole tank for purposes of the test?

By the way, I have to thank you all for taking the time to help me out with your ideas and suggestions.

mongo6407

OK, Torco test complete. Torco had no impact on the sound. I'm bringing the car into the dealer to ask about the chain, guides, tensioner, and cam adjuster. Hopefully replacement of some parts will solve this problem.

jctevere

I know exactly what the OP is talking about. My C250 occasionally makes this sound too. It is not the sound referenced in the YouTube video. The best way I can describe it is that it comes from the front right (when driving in the driver's seat) and sounds like (insert: gurgle, rumble, knock). It is very low pitch, doesn't sound metal or anything. It almost sounds as if you're trying to imitate an engine noise with your mouth and vibrating your lips.

I find that it is more prevalent, especially if you begin driving when the car hasn't fully warmed up yet. You only hear it on low RPM's (1500-2500), which is why it is more common in "E" mode, especially when accelerating slowly.

OP, wouldn't you agree? To be honest, I think its a "normal" noise - as both of our C250 coupes experience this. I would also be willing to bet that it has to do with gas quality, as my brother who occasionally puts in regular fuel, the sound is MUCH more apparent on 87 octane.

mongo6407

Well, the sounds of my car are very pronounced going up hills or even accelerating normally on level ground. It's a cacaphony of clatter in that engine. How MB made getting 200 HP so complicated I will never understand given that a Honda Accord EX can get pretty close in performance without a turbo. If the engine knock is normal, then I want my money back because the less expensive G37 I had with 328 HP sounded like butter and ran on 87 octane. Seriously, this C250 is a luxury car? It's embarrassing to drive the thing.

mongo6407

I do notice that in "S" mode the sound is a little less than when in "E" mode. Definitely something metallic sounding though like I've said before. Initially starts off rustling like maracas or a chain dragging and finishes off sounding like castanets (or VW beetle sound) right after each upshift point (~3000 rpm). It's a regular flamenco dance in there! Once I'm cruising beyond 40 mph I don't hear it unless I suddenly accelerate to pass.

mongo6407

Finally the shop foreman acknowledges the mysterious sound. Hallelujah! Now only if they can find out where it's coming from. The c250 sport I got as a loaner sounds great with 10k miles. Now I remember what the car is supposed to sound like!

Glyn M Ruck

Good news!

mongo6407

Dealer says nothing wrong with my car. It is supposed to sound like crap. That's why it's a C-class and not an E-class. That, in a nutshell, is the voicemail I received.

How is it then that the loaner C250 sounds phenomenal and my car sounds awful if they are supposed to be the same?

Since there appears to be no way to fix the problem, has anyone had any luck in getting a dealer to take a car back? I can't invoke the lemon law unless the problem is something they can fix. If they say it can't be fixed, then I'm stuck. I will never buy another MB product again! Should have bought a Honda.

Glyn M Ruck

Take the loaner back to them & tell them that is how you want your car to sound.