The 2001 XJ8 with the 4.0L AJ-V8 is a comfortable luxury sedan plagued by catastrophic Nikasil cylinder bore failures and aging plastic-heavy cooling and transmission systems. When maintained obsessively they're pleasant, but deferred maintenance turns expensive quickly.
Nikasil Cylinder Bore Failure (Pre-2000 Engine Carryover Risk)
Occasional · high severityTypical onset: 60,000-100,000 mi
Symptoms: Cold-start misfires that clear up when warm, Progressive loss of compression in one or more cylinders, Blue smoke on startup, Check engine light with multiple misfire codes
Fix: Requires complete engine replacement or short-block swap with steel-lined cylinders. 20-30 labor hours depending on accessibility and ancillary work. Some 2001s got updated blocks, many didn't—VIN research critical before purchase.
Estimated cost: $6,000-12,000
Plastic Timing Chain Tensioners and Guides Failure
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Rattling noise from front of engine on cold starts lasting 3-5 seconds, Metallic grinding or slapping from timing cover area, Check engine light with cam/crank correlation codes, Catastrophic failure: sudden loss of power, valve-to-piston contact
Fix: Full timing chain service including tensioners, guides, chains, and variable cam timing components. Engine-out or extensive front disassembly required. 16-22 labor hours. Do NOT defer once rattling starts—catastrophic valve damage occurs rapidly.
Estimated cost: $3,500-5,500
Transmission Cooler Line and Radiator End-Tank Failure
Common · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Transmission fluid in coolant (strawberry milkshake appearance), Coolant in transmission (erratic shifting, slipping), Leaks at radiator side tanks or cooler line quick-connects, Transmission overheating warnings
Fix: Replace radiator (plastic end tanks crack), all cooler lines, flush both systems thoroughly. If contamination occurred, transmission rebuild likely needed. Radiator alone: 4-6 hours. With trans service/rebuild: add 12-20 hours.
Estimated cost: $800-1,200 (radiator/lines only), $3,500-6,000 (with trans rebuild)
Air Suspension Compressor and Strut Failures
Common · medium severityTypical onset: 90,000-130,000 mi
Symptoms: Vehicle sits low, especially overnight (sagging corners), Suspension fault warnings on dash, Compressor runs constantly or won't run at all, Harsh ride with clunking over bumps
Fix: Air struts leak at diaphragms, compressor wears out from overwork. Individual strut replacement: 2-3 hours each. Compressor: 3-4 hours. Many owners convert to coil springs (full conversion kit 8-12 hours) to eliminate chronic issues.
Estimated cost: $600-1,000 per strut, $800-1,200 compressor, $1,500-2,500 coil conversion
Valley Pan Coolant Crossover Pipe Leak
Occasional · medium severityTypical onset: 75,000-110,000 mi
Symptoms: Coolant loss with no visible external leaks, Steam from HVAC vents when heater is on, Slow overheat on highway drives, Coolant smell in cabin
Fix: Aluminum crossover pipe in the valley between cylinder banks develops pinhole leaks or O-ring failures. Requires upper intake manifold removal. 8-12 labor hours. Replace all valley coolant hoses and thermostat housings while in there.
Estimated cost: $1,200-2,000
Throttle Body Failure and Idle Control Issues
Occasional · low severityTypical onset: 80,000-120,000 mi
Symptoms: Surging idle or stalling when coming to a stop, Check engine light with throttle position/idle control codes, Reduced power mode, limp-home operation, Erratic throttle response
Fix: Electronic throttle bodies fail internally (motor or position sensors). Replacement throttle body requires calibration with factory scan tool. 2-3 labor hours including programming.
Estimated cost: $600-1,000
Buy only with comprehensive service records and a $5k repair fund—these are money pits for the unprepared, but rewarding for enthusiasts who wrench or have a trusted specialist.
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.