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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53902
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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380sl: Have a 1984 380sl Mercedes. I was told by mechanic

Customer Question

Have a 1984 380sl Mercedes. I was told by mechanic that the timing chain and rails needed to be replaced because it was loose and plastic guides were broken. He said that they could here a rattle when the engine is first started. He also said that Mercedes replaced these, because they were breaking, some time ago if owner would pay half the cost. Ours was never changed. I talked with two other mechanics. None of us could hear the rattling and one said that with 80,000+ miles you shouldn't need to replace the timing chain. He also said that Mercedes does not use plastic parts. This is a $1400 fix and I don't know who to believe. Please advise. Thank you.
Also the car is running at 90c to 98c. This is after the first mechanic removed and cleaned the radiator fins and replaced the relay switch. The second mechanic replaced the thermostat. So, the electric fan is working, the fan clutch is locking up and it's a new thermostat. Both mechanics test drove the car and said it is not over heating. Is the car running at acceptable temperature?
Submitted: 2 years ago.
Category: Mercedes
Expert:  Tim Mohr replied 2 years ago.
Hi my name is ***** ***** only 80k miles, the timing chain should not need replacement, its very unlikely, and if yu dont here a rattle at idle or at start up, you should have nothing to worry about, and 90C to 98C is normal operating temp for these, it can go as high as 100c with out and worries, it is running exactly where its suppose too,Tim
Customer: replied 2 years ago.
Have you heard anything regarding the failure of the "plastic" rails that fail and Mercedes offer to pay half the cost? This was probably some time ago. Thanks, Jim
Expert:  Marty replied 2 years ago.
Hi, perhaps I can help. My name is***** of the upper timing chain guide rails on this model is very common. If you ignore the problem the broken guide rail can eventually lodge between the timing chain and gear and cause the chain to jump timing. This will result in severe valve damage and possible a broken piston. The first mechanic is correct in advising you to replace the rails but the rails only need to be replaced if they have already cracked. If the rails are still in one piece you can get away with just replacing the timing chain tensioner. The tensioner is the source of the problem. When the car is off, a worn tensioner will collapse and allow the chain to slacken. When you start the motor the chain slaps against the plastic upper chain rails and eventually cracks them. The problem occurs on the left side cylinder head. The mechanic should remove the valve cover and inspect the upper guide rails in the left head. If the rails are cracked they will need to be replaced along with the tensioner. The chain does not need to be replaced for this problem.Let me know if you have any questions. Marty