rattling in engine
 

I have a 96 SL320 with 114k on it. When I rev the engine and it goes back down to idle, there is an interval when I hear a rattling sound. Engine performance is good, responsiveness is good, no problems with operations, I can only hear this when I am under the hood, not while inside the car. What should I check? I replaced the belt, tensioner pulley, and idler, and water pump, still a bit of a rattle. Timing chain? When I had the upper timing chain cover off, all looked great. Any help is appreciated.
Happy Benzing!
Brian

It may be the timing chain tensioner. A bad tensioner in our 1992 300CE caused a sound like you describe. The dealer's Service Department removed the valve cover to confirm. Their first response was to ignore the sound until it got worse, but I wanted to avoid potentially serious consequences by addressing the situation immediately.

Thanks, Fred,
What did they do, replace the chain and tensioner? I am sure if I replace the tensioner I might as well replace the chain, and might as well replace the head gasket, since it is the original one, eeekk! Thanks,
Brian

Brian, the dealer replaced the tensioner only. It must have had a leaking seal because it relies on oil pressure to function properly. I was surprised that it failed at 80,000 miles. No real reason to replace the timing chain at that mileage. The head gasket was previously replaced under Starmark Warranty. I'd confirm that the tensioner is faulty before replacing it. Diagnosis may be difficult because a local independent mechanic listened to the engine and thought that it was OK. The dealer listened with a stethoscope and couldn't identify the source of the noise until they removed the valve cover and did some visual checks. I knew that there was a problem because the noise was one that I had never heard before with the engine idling and the hood up.

I have the same issue on my 190E. I thought it was the timing chain, but after further investigation and a new tensioner installed I have found that it is actually my water pump pulley. Either the pulley is loose on mine or the bearings are starting to fail. I can move my pulley a few Milimeters! Check the water pump and all pulleys for slight wobble.

Thanks for the info! There is one thing I have known about MB's is that when you hear a noise, something is wrong! I have just replaced my water pump and both pulleys, and belt, It was at 114k, so it was time. Of course the bearings in an accessory may be failing and causing the rattle, I have noticed that the AC compressor is noisy while in operation, so many things spinning around under there, who knows! I don't give up easily and I will figure it out sooner or later!
Happy Benzing!
Brian