I recently got a letter from MBUSA stating that you should use synthetic oil in the ML320. That makes sense, because with the Flexible Service Interval feature you can go up to 18,000 miles between oil changes. However, I have also seen claims that you should use synthetic in a diesel also. This would seem to be awfully expensive; due to loading with soot particles, you have to change the oil in a diesel every 3500 miles or so, no matter what kind of oil it is. I'd think the benefit of the synthetic oil would be negated by the extreme added cost (unless you have a special case like very low temperature operation). Does anybody have an informed opinion on this?

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Bill
- 1991 300D Turbo 2.5
- 2000 ML 320