The 986-generation Boxster S (1997-2004, though note: there was no '718' designation in 2001—that's the modern 2016+ era) is a brilliant mid-engine sports car hampered by one catastrophic flaw: intermediate shaft (IMS) bearing failure and resulting engine destruction. When it goes, it takes the whole motor with it.
IMS Bearing Failure & Catastrophic Engine Damage
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Metal shavings in oil during changes, Metallic rattling from engine bay at startup, Sudden loss of oil pressure, Complete engine seizure without warning
Fix: The single-row IMS bearing fails, grenading the engine. Preventive replacement requires engine-out or transmission-out access (12-18 hours labor). Once it fails, you're looking at full engine rebuild or replacement. Many owners do IMS retrofit + RMS + clutch together since transmission is already out.
Estimated cost: $2,500-4,000 preventive IMS bearing job; $12,000-18,000 engine rebuild after failure
Rear Main Seal (RMS) Oil Leak
Common · medium severityTypical onset: 50,000-90,000 mi
Symptoms: Oil pooling under car after sitting, Oil dripping from bell housing area, Visible oil on transmission housing, Oil consumption without visible leaks elsewhere
Fix: The RMS leaks due to poor factory seal design and material degradation. Requires transmission removal for access (10-14 hours). Always done alongside IMS bearing service to avoid doing the job twice.
Estimated cost: $1,800-2,800 standalone; $500-800 added if done with IMS work
Coolant Expansion Tank & Hose Failure
Common · high severityTypical onset: 70,000-120,000 mi
Symptoms: Coolant smell in cabin or engine bay, Visible coolant leaks near left side of engine, Low coolant warnings, Overheating, Cracked plastic tank visible on inspection
Fix: The plastic expansion tank becomes brittle and cracks, or the connection hoses split. Can cause rapid coolant loss and overheating damage. Tank replacement is straightforward (2-3 hours), but many techs also replace all aging coolant hoses preventively since access is the hard part.
Estimated cost: $400-800 for tank and immediate hoses; $1,200-1,800 for full coolant system refresh
Air-Oil Separator (AOS) Failure
Occasional · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Blue smoke from exhaust on startup or deceleration, Excessive oil consumption (1 qt per 1,000 mi or more), Oil in intake tubing or throttle body, Rough idle
Fix: The AOS membrane fails, allowing oil to be sucked into the intake. Requires replacement of the entire AOS unit. Access is tight but doable without engine removal (4-6 hours). Use OEM or quality aftermarket—cheap units fail quickly.
Estimated cost: $800-1,400
Transmission Synchro Wear (Manual)
Occasional · medium severityTypical onset: 80,000-130,000 mi
Symptoms: Grinding or difficult engagement into 2nd or 3rd gear, Requires double-clutching to shift smoothly, Gear clash when cold, Pops out of gear under load
Fix: Second and third gear synchros wear, especially if driven hard or with delayed shifts. Transmission rebuild requires removal (8-10 hours removal/install) plus internal work (10-15 hours rebuild). Many opt for used transmission swap instead.
Estimated cost: $3,500-5,500 rebuild; $2,500-4,000 used transmission swap with labor
Convertible Top Hydraulic System Leaks
Common · low severitySymptoms: Slow or jerky top operation, Hydraulic fluid stains in trunk area, Top fails to latch or unlatch, Pump runs longer than normal
Fix: Hydraulic lines, cylinders, or pump seals degrade over time. Diagnose which component is leaking (1-2 hours), then replace lines, cylinders, or pump as needed (2-6 hours depending on component). Fluid is messy and gets everywhere.
Estimated cost: $600-2,000 depending on which components need replacement
Fantastic driving experience, but only buy one with documented IMS bearing service or factor $3k-4k into your purchase price immediately—this is non-negotiable unless you enjoy grenaded engines.
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.