Erm.. I find BMW NA engine oil in my E90 N46B20 degrade (turn black and thickening) much faster then my Avanza.
My puny Avanza 1.3L engine despite small CC, I frequent drove it at 4~5k rpm.. for above 140kph cruising, no to mention toll booth shoot outs.. :4:
Few possible reasons I can think of, my E90 is lady driven, frequent short distance compare to my puny Avanza la. That too would contribute to ageing of the BMW engine oil by comparison.
Or is it my Toyota Genuine Fully Synthetic 5w-40 is far more superior than those of Torco, Castrol, Liqui-Moly, 0w-30, 5w-30 and 0w-40 that I've used for my N46B20? At least my 8 years old 220k km old Avanza valve seal still intact and not losing any oil for 10k km oil change interval. The N46 valve seal failed big time, despite less than 6 years old, less than 95k km.
There's one more critical element affecting the ageing of engine oil and that's heat. BMW engine runs a lot hotter than my Avanza engine. Which killed the oil and perhaps my valve seal too..
Now back to F30.. does the engine oil being circulated to the twin scroll turbine for lubricating and cooling purposes like conventional turbo engine? If so, doesn't that automatically means your engine oil fail a lot faster than NA BMW engine? For a Scooby, 6k km is about max you can push the oil change interval. I know some are doing it every 3k km, even that, the difference in engine performance can be felt instantly.
Food for thoughts..
