Just read this thread and it don't smell good. It sounds like your engine was running perfectly fine then you start to hear this racket while driving. Oil is full and coolant is fine. Why are you suspecting a broken piston ring? Low compression in one cylinder or a broken piston ring would not make the noise you described.

Did you start the engine with all the belts removed and see if the noise is still there or not? You can run the engine without belts safely for less than 15 seconds. Were you there witnessing the compression test? Shops are there to make money and 75% of auto repair shops are dishonest. Can you trust your shop?

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked