The 2014 S5 with the 3.0T supercharged V6 is generally solid, but catastrophic engine failures from carbon buildup and oil consumption plague higher-mileage examples, often requiring complete rebuilds. The dual-clutch transmission (S tronic) has its own oil cooler and mount weaknesses that need attention.
Catastrophic Engine Failure from Carbon Buildup and Oil Consumption
Occasional · high severityTypical onset: 80,000-130,000 mi
Symptoms: Excessive oil consumption (1 qt per 1,000 mi or worse), Misfires, rough idle, loss of power, Check engine light for multiple cylinder misfires, Catastrophic failure: knocking, seized pistons, spun bearings
Fix: Direct injection causes intake valve carbon buildup leading to poor sealing and oil burning past rings. If caught early, walnut blasting valves and new PCV can help (4-6 hours), but advanced cases need full engine rebuild or short block replacement (25-35 hours labor). Pistons, rings, bearings, and sometimes crankshaft damage from oil starvation.
Estimated cost: $12,000-18,000
Transmission Oil Cooler Failure
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Transmission fluid leaking from front of vehicle, Overheating transmission, hard shifts or slipping, Transmission warning light
Fix: The auxiliary transmission oil cooler develops leaks at seals or cracks internally. Requires removal and replacement of cooler unit plus complete transmission fluid flush. 3-5 hours labor. Ignore it and you cook the dual-clutch mechatronic unit ($5k+ additional).
Estimated cost: $800-1,400
Transmission Mount Failure
Common · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Clunking on acceleration or deceleration, Excessive driveline vibration, Visible transmission sag or torn rubber mount
Fix: The rear transmission mount tears and allows excessive drivetrain movement. Simple replacement but requires supporting transmission on jack. 2-3 hours labor. Often replaced alongside engine mounts.
Estimated cost: $400-700
Thermostat Housing Coolant Leak
Occasional · medium severityTypical onset: 60,000-90,000 mi
Symptoms: Coolant smell in engine bay, Visible leak at front of engine, Low coolant warning light, Overheating if ignored
Fix: Plastic thermostat housing cracks or o-rings fail. Must replace entire housing assembly and sometimes coolant flange. 3-4 hours labor with front-end disassembly for access.
Estimated cost: $600-1,000
Supercharger Snout Bearing Failure
Rare · high severityTypical onset: 90,000-140,000 mi
Symptoms: Whining or grinding noise from front of engine, Noise increases with RPM, Check engine light for boost pressure faults, Complete loss of boost if bearing seizes
Fix: The front bearing on the supercharger input shaft wears out. Requires supercharger removal and rebuild or replacement. 8-12 hours labor. Can grenades and send metal through intake if it catastrophically fails.
Estimated cost: $3,000-5,000
PCV System Failure Leading to Oil Leaks
Common · low severityTypical onset: 50,000-90,000 mi
Symptoms: Oil residue around valve covers, Oil consumption without visible leaks, Rough idle, Whistling or hissing from engine bay
Fix: Diaphragm in PCV valve fails, causing crankcase pressure issues and pushing oil past gaskets. Replace PCV valve and associated hoses. Often done with valve cover gaskets. 4-6 hours labor if doing full job.
Estimated cost: $800-1,400
Buy one with full service history under 60,000 miles or expect to budget for a potential engine rebuild — when they're good they're great, but engine failures are too expensive to gamble on high-mileage examples.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.