S85B50

The S85 has a well-documented tendency toward rod and main bearing failure, often leading to total engine destruction. The engine's F1-derived design demands constant adequate oil pressure; any lapse — cold starts driven hard, low oil level, or extended intervals — accelerates bearing wear catastrophically. High-mileage examples are especially vulnerable.

The S85 uses ten individual throttle bodies, each with actuator gearing and MOSFET control boards that are prone to wear and failure. This is described as an 'infamous' and well-known issue in the community. Replacement of the gearing and MOSFET components is a documented repair, but parts and labor costs are significant.

Forum data indicates oil temperature running high in warmer conditions and under spirited driving. The oil cooling system must be fully functional; a compromised oil cooler, thermostat, or blocked passages leads to accelerated bearing and engine wear given the S85's tight tolerances.

The E60 M5 was equipped with the SMG III sequential manual gearbox, which has its own reliability concerns separate from the engine but closely linked to ownership experience. Community data notes the SMG clutch and actuators need monitoring, particularly on higher-mileage examples.

Due to the F1-inspired design, the S85 requires careful cold-start procedure. Driving hard before the engine reaches full operating temperature — especially oil temperature — is a primary cause of premature bearing wear. This is an ongoing operational risk throughout the engine's life, not a mileage-specific failure.