The 2015 Cayman S with the 3.4L MA1.21 flat-six is the last of the naturally-aspirated 981 generation before the 718 turbo-four changeover in 2017. Generally solid, but suffers from bore scoring risk, IMS bearing concerns carried over from earlier designs (though revised), and typical Porsche cooling system fragility under track use.
Cylinder Bore Scoring and Piston Ring Failure
Occasional · high severityTypical onset: 60,000-100,000 mi
Symptoms: Cold-start smoke (blue-gray haze), Oil consumption 1+ quarts per 1,000 miles, Loss of compression in one or more cylinders, Metallic ticking from engine bay, Check engine light with misfire codes
Fix: Requires engine removal, complete disassembly, bore inspection, cylinder liner installation or block replacement, full rotating assembly work. 40-60 hours labor depending on machine shop turnaround. Often triggers full rebuild including IMS bearing replacement, AOS, clutch, and RMS while engine is out.
Estimated cost: $15,000-25,000
IMS Bearing Failure (Intermediate Shaft)
Rare · high severityTypical onset: 80,000-120,000 mi
Symptoms: Metallic grinding or whirring from rear of engine, Metal flakes in oil filter during changes, Catastrophic engine failure without warning in worst cases, Oil pressure fluctuations
Fix: Preventive replacement recommended during clutch jobs or major engine work. Requires transmission removal, flywheel off, then bearing extraction and installation. 12-16 hours as standalone job. Many owners opt for LN Engineering or Hartech upgrade bearing kits. If bearing fails, expect full engine teardown for debris cleanup.
Estimated cost: $3,500-5,500
Coolant Expansion Tank and Radiator Failure
Common · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Coolant smell in cabin or near front trunk, Visible coolant weeping from tank seams, Overheating warnings on gauge, Low coolant warnings after topping off repeatedly, Cracked plastic at mounting tabs
Fix: Plastic expansion tank cracks at weld seams or mounting points, especially on track-driven cars. Side radiators also develop end-tank leaks. Tank replacement is 2-3 hours, radiators are 4-6 hours each (requires bumper removal and condenser work). Replace both radiators and tank together to avoid comebacks.
Estimated cost: $1,200-2,800
Transmission Oil Cooler Line Leaks
Occasional · medium severityTypical onset: 50,000-90,000 mi
Symptoms: Transmission fluid spots under car (red/pink fluid), Burnt transmission fluid smell, Transmission temperature warnings, Slipping or delayed shifts under load
Fix: Hard lines and rubber sections corrode or crack where they run along underbody. Requires lift access, sometimes subframe lowering for routing. 3-5 hours labor plus refill and bleeding. PDK fluid is expensive ($30+/liter, needs ~8 liters). Inspect all cooler lines and connections during repair.
Estimated cost: $800-1,500
Air-Oil Separator (AOS) Diaphragm Failure
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Excessive oil consumption without external leaks, White smoke from exhaust on startup, Oil in intake tubing or throttle body, Rough idle when cold, Check engine light with mixture codes
Fix: Internal diaphragm tears, allowing crankcase pressure to push oil into intake manifold. Located under intake manifold on driver side. 4-6 hours labor including manifold removal. Use OEM Porsche part—aftermarket units fail prematurely. Good time to replace valve cover gaskets and spark plugs while access is open.
Estimated cost: $1,200-1,800
PDK Transmission Mount Failure
Common · low severityTypical onset: 50,000-80,000 mi
Symptoms: Clunking when shifting from Park to Drive, Vibration at idle in gear, Driveline shudder during acceleration, Visible transmission sag on lift
Fix: Rubber transmission mount deteriorates, allowing excessive movement. Requires exhaust removal for access, 2-3 hours labor. Replace both left and right mounts simultaneously. Aftermarket polyurethane mounts available for track cars but increase NVH.
Estimated cost: $600-1,000
Fuel Pump and Filter Assembly Clogging
Occasional · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Hesitation or stumble during hard acceleration, Limp mode activation under sustained high RPM, Fuel pressure codes, Difficult cold starts, Stalling after high-speed runs
Fix: In-tank fuel pump assembly and integrated filter degrade over time, especially with ethanol fuels. Requires fuel tank drop (4-5 hours labor). Replace entire pump assembly—filter is not separately serviceable. Flush tank if contamination found. Porsche revised design multiple times; use latest supersession part number.
Estimated cost: $1,500-2,200
Buy a well-documented example under 60k miles or budget for an engine rebuild; the driving experience is worth it, but only if you can afford the insurance policy of proper maintenance and eventual engine work.
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.