1999 SL 500.The car has 58,000 miles, last oil change at 57,000 miles Mobil1 full syntetic 0w40, OEM filter. the knocking only appears when the temperature is below 50F or abouts, it last for about 3 to 5 seconds and it goes away, it seems to be coming from the front driver side of the engine and can be hear above the normal sounds, air pump etc. after it goes away a ticking sound like a lifter can be hear for about 10 to 15 seconds and that one goes away too. I've tried to pinpoint the exact location of the knock but I'm not fast enough and can't get the wife to get up that early in the morning to turn the key for me. I am very concern about this and will appreciate any help, advise, you guys have help me a lot in the past and I thank you.

I see lots of "carbon knock" issues during the cold weather months. GM Top Engine Cleaner works great. Just pull a spark plug out of each cylinder and pour it directly into the cylinder. Let it sit over night and then crank the engine to empty the cylinders. Re-install the plugs and take it for a good ride. Don't forget to change the oil and filter when you're done. Between September and April I do several cars a week using this method and it works great. If you don't want to use the GM product, Techron fuel additive is a good second choice. It'll get the job done, but it takes awhile.

I have a slight knocking sound that lasts for a few mins until the engine is completely warm on my 99 C230K and is only audible from inside...however its the sound of a classic 4 cylinder when cold but I cant stand it.

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99 C43
98 S420
99 C230K
01 C240

I'll try the slow approach with the techron, I don't know where to get it besides the Chevron pump, can it be purchased by itself, auto parts maybe?

I buy mine through the local auto parts/supply house.

Thank you Sir.

use thicker oil. is the 0w40 recommended for your car?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

That is the MB dealer recommendation, from the service manager, they service all the MB vehicles with the Mobil1 0W40.

The knocking is staying longer and longer now, untill the engine reaches operating temperature no matter of the outside temperature, I'm about half in my second tank of fuel laced with techron, needless to say I'm really worried .

I think it's time to use the GM stuff. If the noise doesn't go away it's not a carbon knock. Good luck.

After 4 tankfulls of premium Amoco fuel from BP with a bottle of Techron each the knocking is gone, it diminish a little bit at a time but this morning the temp was 42 F and not a slight knocking from the engine, it makes my day.
Thanks to everybody that responded, now If I can fix the rough idle I will really be happy.

Since your car has been running on Techron for awhile you can rule out dirty injectors as a cause for the rough idle . I get lots of rough idle complaints on M112/113 equipped MB's, especially after about 50K. If it's only slightly rough there won't be any fault codes. A new set of ignition wires makes them run like new again. The wires aren't cheap though, so make sure you check the obvious stuff before replacing them. Keep us posted.

Brand new set of Beru wires installed 3 weeks ago, slight improvement, MAS sensor gaskets top and bottom replaced, most vacuum lines and fittings replaced, air filters replaced, about to Miti-vac thru vac lines looking for a leak, any other parts I need to check, no engine light.

Don't overlook the engine mounts.

Replaced December 28