This kind of damage is typical for engines that use low viscosity engine oils with a low shearing resistance. This also is most plausible for this particular S50B32 engine, especially since BMW allowed the use high performance synthetic oil with a viscosity rating of 5W30 for cars prior to 1998 since 2001 without making a distinction between M-cars and non-M cars.Jeroen wrote:Het bovenste lager van de 6e cilinder, ook het meest kwetsbaar, is inmiddels ook door z'n tweede laag heen dus die was echt al een eind heen. Gelukkig ook hier geen schade aan de krukas
The discrepancy is hidden in the exact specifications of BMW High performance synthetic oil. Research carried out by m5board member ‘ard’ proves that the kinematic viscosity of this type of oil is 11.9cst at 100°C, which is close to the upper limit of an SAE30 weight oil and the transition border (12,5cst) to an SAE40 type of oil. It is a fact though that many dealers select their own suppliers or revert to commercially available oil-types. However, the SAE30 ranges between 9.8 and 12.5cst at 100°C. Whilst 11.9cst may be within the margings for an S50B32, garden variety xW30 oil will range more between the lower-to mid scale of this range, which not only is too low by itself, but also the spec for the monograde SAE-range. Multigrades generally have difficulty reaching the SAE-specs for monogrades. Add to that the S50's habit for dilluting the oil with fuel and the long-life spec of 5W30 oil......... I'll let you be the judge.