The Oil discussion is a long discussion, but to make it short and understandable, you must realize the M30 base inline 6 which the last ones were installed on 1993 535s, 735s have more tolerances in internal components then a M50s, M52s, M60s, M62s and newer engines, so for that reason the oil grades like 0/30 up to 10/60 syntactic are created to serve the range of the motors that made with new technology and precise manufacturing parts and almost 0 tolerances. But in case of older engine you must use thick and additional wear protection agent such as Zink in which helps the oil to cover and fill the larger internal tolerance that the motor would work smoothly and with out burning oil, leaking oil and premature worn out parts.
I personally use 20/50 syntactic with Zink additive in my B10, B11
15/50 syntactic on my Dinan e39 M52
10/60 syntactic with Zink additive on my B7 Turbo
5/40 syntactic in my Audi A3 2.0 T
and if I finish my S54 engine swap I have to use 10/60 syntactic.
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