The 2005 XK8 is the final year of the first-generation X100 platform with the AJ27 4.0L V8. While elegant and enjoyable to drive, it's plagued by catastrophic Nikasil cylinder liner failures and classic British electrical gremlins that make it a high-risk used purchase without documented engine work.
Nikasil Cylinder Bore Failure (AJ27 V8)
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Cold-start rough idle or misfire that clears when warm, Loss of compression in one or more cylinders, White smoke on startup, Check engine light with multiple misfire codes, Catastrophic failure if driven hard when damaged
Fix: Nikasil-lined bores wear excessively with sulfur in fuel. Fix requires complete engine rebuild with steel liners or replacement short block. 40-50 labor hours for removal, rebuild, and reinstallation. Many owners opt for used engine swap from post-2000 steel-lined blocks.
Estimated cost: $8,000-15,000
Plastic Timing Chain Tensioners and Guides
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Rattling noise from front of engine on cold start, Timing chain noise that persists after warm-up, Check engine light with cam/crank correlation codes, Catastrophic engine damage if chain jumps timing
Fix: Plastic tensioners and guides deteriorate with age and heat. Requires front engine disassembly to replace tensioners, guides, and chains on both banks. 18-24 labor hours. Always replace water pump and thermostat while in there.
Estimated cost: $3,500-5,500
Transmission Oil Cooler and Line Failures
Common · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Transmission fluid leaking from radiator area, Pink residue or drips under front of car, Harsh shifting or slipping if fluid level drops, Coolant in transmission fluid (milky appearance) if internal cooler fails
Fix: External cooler lines corrode and leak; internal radiator cooler can fail and cross-contaminate fluids (requires transmission flush and possible rebuild). External line replacement: 2-3 hours. Internal cooler failure with flush: 8-12 hours if trans needs service.
Estimated cost: $400-1,200 for lines; $2,500-4,000 if trans contaminated
Throttle Body and Idle Air Control Valve Issues
Common · low severityTypical onset: Any mileage
Symptoms: Erratic or high idle (1,200-1,800 RPM), Stalling at stop lights or when coming to rest, Surging idle in park or neutral, Check engine light with idle control codes
Fix: Carbon buildup on throttle plates and IAC valve causes erratic idle. Cleaning often temporary fix; replacement throttle body usually needed. 2-3 hours labor for proper diagnosis and replacement.
Estimated cost: $600-1,000
Convertible Top Hydraulic System Leaks
Occasional · medium severityTypical onset: Any mileage
Symptoms: Top operates slowly or stops mid-cycle, Hydraulic fluid leaks in trunk area, Top won't latch or unlatch, Pump runs continuously or makes grinding noise
Fix: Hydraulic rams, lines, and pump seals fail with age. Diagnosis requires pressure testing system. Ram replacement: 4-6 hours. Pump rebuild: 3-4 hours. Often multiple components need attention simultaneously.
Estimated cost: $1,200-2,500
Engine and Transmission Mounts
Common · low severityTypical onset: 80,000-120,000 mi
Symptoms: Clunking when shifting from park to drive or reverse, Excessive vibration at idle, Engine rocks noticeably during acceleration, Transmission thunk on throttle lift
Fix: Hydraulic mounts fail and leak fluid. Engine has 4 mounts, transmission has 2. Typical to replace all 6 at once. 5-7 hours labor for complete set.
Estimated cost: $1,500-2,200
Suspension Bushings and Ball Joints
Occasional · medium severityTypical onset: 70,000-100,000 mi
Symptoms: Clunking over bumps, Wandering steering or poor tracking, Uneven tire wear, Steering wheel off-center after hitting bumps
Fix: Front lower control arm bushings, ball joints, and rear subframe bushings wear. Front control arms often replaced as assemblies. Rear subframe bushings require subframe drop. 8-12 hours for comprehensive front/rear refresh.
Estimated cost: $2,000-3,500
Avoid unless the Nikasil engine has been replaced or rebuilt with steel liners and timing chains are fresh — otherwise you're buying someone else's $15,000 repair bill.
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.