Sometimes there's a rattling sound you hear on start up, and then it quiets down after awhile.

I'd suspect you are due. I know for the 8 cylinder engines they recommend chabging out the timing chain, tensioner and plastic guide rails every 100,000 miles or so...

These cars are very reliable, and the 6 cylinder engine is VERY robust, but by now you could be tempting fate, if the chain slips, and lets go, the pistons could collide with.....well, we are talking about a major catastrophe, let's not go there, and by now especially the guide rails, are probably pretty brittle, and maybe about to crumble, so go ahead and plan to replace the chain tensioner and guide rails, so as to be on the safe side.

The Indie mechanic I like had an '83 380SL bought in with a major engine failure because the chain had slipped. What makes it a story was that the car had been brought in for the timing chain to be changed, and it was, but the mechanic did the job at another shop WITHOUT changing the guide rails, and the new chain slipped-again! So, the mechanic changed the chain again and AGAIN he did not replace the guide rails, and the timing chain slipped ANOTHER TIME, and this time the guide rails just crumbled completely and the damage was repeated yet again!!

At this point the customer switched mechanics and went to my Indie, and I was there at this point to see the poor car with the engine torn down for the 3rd attempt. My indie knew what had happened and why, But the customer didn't realize.

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)