Has anyone out there had or have this problem ? I have a 2009 C-350 Sport, and when I start the engine after it has been sitting awhile, the engine will knock on startup for about 2 seconds, the dealer cannot located this knock, but they say it is probably spark knock and use Techron in the fuel tank, that does not affect it.

Any ideas ?

Thanks.
Debrunsky

 

Spark knock on startup? Wow. I never heard that one! Usually spark knock occurs under a load of some kind and can be octane/timing based. Older cars it can be carbon build-up in the cyl. head, but in your case.....a new car and spark knock for the first two seconds? I'm not buying that at all. Here's my suggestion: Be sure you document your visit to the dealership over this matter and later on, if it turns out to be something else, you'll be in good shape. Now, having said this, my '05 C230 four cyl. has been doing this for 100k miles, and the car now has about 167K on it. Dead cold, on startup, it will do this but I think it's simply an initial oiling symptom whereby the engine oil doesn't get up to pressure for a second or two and things are a bit noisy.......but........just for a second until the oil pressure is higher and then it's gone.

 

Thanks for the feedback, I will agree that spark knock is too farfetched to believe, I think it may be the timing chain adjuster not getting enough oil to take up the slack when starting.

 

i own a 07c230 sport with about 27000 miles on it at first the dealer said it was a spark knock so changed fuel but i use premiun anyway so i changed gas station jhust in case but it was still there so i took it back and now the dealer say it was normal before the noise is coming from the intake. they say the noise is when the intake runners are switching from the short runners to the long runners. and this is suppose to be normal. the noise its must sound like a spark knock cause at first he said that was the problem any body out there heard of this or owns a c230 with the 2.5 v6 thats hearing the same noise??????

 

I have the same noise but I heard it form the belt tenssioner out side of the engine

 

Here's another way you can see if it's what they said it was....ie.....spark knock. Go get a bottle of the Chevron Techron fuel inj. cleaner. It's at all the auto parts stores. Be careful, there are several ones that look the same. Get the one that treats "up to 21 gallons" or so.
It costs about 8-10 bucks per bottle. Just get one. It's in a black bottle with a skinny neck to fit in your gas tank. OK. Run the car down to about 4-5 gallons, and pour this stuff in the tank, then fill with about 8 more gallons. Premium, of course. Then drive it around for the next few days and listen for that noise after about two or three days. If it's gone, it was spark knock. If not, that rules out what "they couldn't find". This stuff REALLY works. Some do and some don't, but this one does. I have had the same probs. with my other car and it cured the spark knock problem the next day. Now, if it's still there, take the car back to the dealer and tell them you're going to leave it with them until they find it under warranty, and you need a loaner MB to drive in the meantime. They can put one guy in the car to start it and another with the hood open to listen closely for the sound under there as well.