I remember reading somewhere that there was a technical service bulletin for the M104s of that vintage (same as mine) that the oil dipstick isn't calibrated properly, and if you fill the oil up until it shows full on the dipstick you are actually over filling by about a half litre. Whenever I change the oil on mine I only fill it up until the oil reads half way between the "add" and "full" marks on the dipstick.

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Jonathan

2011 Mazda2
2000 E320 4Matic Wagon
1994 C280 (retired)