"There are a handful of small issues, common across all BMWs, such as HPFP failure, carbon build-up, etc. but overall, nothing that should be a serious red flag for any potential buyers."
SOLID
68/ 100
"Track-capable engine, but respect the maintenance"
The S55 uses a friction-fit crank hub rather than a keyed design. Under high load or track use, the hub can slip on the crankshaft, causing catastrophic timing loss and potential engine destruction. BMW acknowledged the issue but determined warranty fixes were more cost-effective than a redesign. Aftermarket keyed crank hub upgrades are widely considered a must-do by the community.
Timing faults or codes
Rough running at high RPM
Loss of power under load
Check engine light
DIY: Hard – requires special tooling and engine bay access
HPFP failure is a known issue across BMW's direct-injection lineup including the S55. Symptoms can be sudden and leave the car undriveable. Forum data confirms this as one of the most cited reliability concerns on the S55.
Hard starting or no start
Rough idle
Loss of power
Fuel pressure fault codes
DIY: Moderate – accessible but requires fuel system knowledge
Carbon Build-Up on Intake Valves€400–900 · 60,000–120,000 kmHIGH
As a direct-injection engine, the S55 does not wash intake valves with fuel. Carbon deposits accumulate over time on the back of intake valves, reducing airflow and performance. Forum data explicitly flags this as a known recurring issue on the S55.
Rough idle
Hesitation on acceleration
Reduced power
Increased fuel consumption
DIY: Hard – requires intake manifold removal and specialist equipment
Intercooler Leaks (OEM and Aftermarket Units)€300–900 · 50,000–130,000 kmMODERATE
OEM intercoolers on the S55 have been reported to develop leaks, reducing charge-air cooling efficiency and potentially causing boost pressure loss. Forum posts specifically document coolant or pressure leaks from the intercooler system, including from aftermarket units if improperly fitted.
Drop in boost pressure
Coolant loss
Reduced performance
Overheating under load
DIY: Moderate – accessible with basic tools
Oil Consumption and Cooling System Stress Under Track Use€200–600 · 40,000–100,000 kmMODERATE
The S55 features additional oil cooling systems designed for track use, but owners who use the car on track must monitor oil levels closely. Elevated oil consumption and cooling system wear are noted in community data, particularly if the car has been used hard.
Low oil warning light
Oil consumption between services
Overheating on track
DIY: Easy – monitoring only; repairs vary
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Buying Checklist
Confirm aftermarket keyed crank hub has been installed — this is a non-negotiable safety upgrade on the S55
Request evidence of walnut blasting or borescope inspection of intake valves within the last 60,000 km
Pressure test the intercooler system and inspect all hoses for leaks or coolant staining
Read fault codes with a BMW-compatible OBD tool and specifically check for HPFP and timing-related codes
Check oil level and condition; ask for service records showing oil changes no longer than every 8,000 km
Verify both airbag recalls (side/window and frontal driver inflator) have been completed by a BMW dealer
Service Reality
Community oil interval8,000 km
Oil specificationBMW LL-04 compliant 0W-40 or 10W-60 for track use (e.g., Castrol TWS 10W-60)
Est. ownership cost (2yr)€1,500–3,500/year depending on track use, including oil changes, minor repairs, and preventive upgrades
The BMW S55 is a capable and rewarding engine that holds up well when properly maintained, but it rewards diligent owners and punishes neglect. The single most important pre-purchase item is confirming the crank hub has been upgraded — skipping this on a used car is a serious risk. Budget for walnut blasting and a fresh HPFP inspection early in your ownership to avoid the most common costly failures. If you find a well-serviced, high-mileage example with documented maintenance, the S55 can be a genuinely reliable performance engine.
Parts People Buy
Keyed Crank Hub Upgrade Kit (S55)Link unavailable
BMW S55 High-Pressure Fuel Pump (HPFP)Link unavailable