The 2004 XK8 with the 4.0L AJ-V8 is a beautiful GT that suffers from one catastrophic engine flaw and typical Jaguar electrical quirks. If the Nikasil issue has been addressed, they're surprisingly solid; if not, you're on borrowed time.
Nikasil Cylinder Liner Failure (Early AJ-V8 Engines)
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Excessive oil consumption (quart per 500-1000 miles), Cold-start misfires that clear when warm, Loss of compression on multiple cylinders, Blue smoke on startup, Rough idle that worsens over time
Fix: Complete engine rebuild or replacement. Nikasil-lined cylinders were susceptible to sulfur in poor-quality fuel causing bore scoring. Factory switched to steel liners mid-2000 (VIN check: A00083 and later typically safe). Rebuild requires boring cylinders, new pistons, rings, bearings. Figure 40-60 hours labor for full rebuild, or 18-25 hours for used engine swap.
Estimated cost: $8,000-15,000
Plastic Thermostat Housing and Water Pump Failure
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: Coolant leaks pooling under engine, Overheating after highway runs, Visible cracks in thermostat housing, Squealing from water pump bearing, Temperature gauge fluctuations
Fix: Plastic thermostat housing becomes brittle and cracks; water pump impellers fail. Always replace both together with all hoses in that area—you're already in there. Requires removal of supercharger on supercharged models (not yours, but same engine family). 4-6 hours labor.
Estimated cost: $800-1,400
Transmission Oil Cooler and Mount Failure
Common · medium severityTypical onset: 80,000-130,000 mi
Symptoms: Transmission fluid leaking onto exhaust (burning smell), Clunking when shifting from Park to Drive, Excessive drivetrain movement on acceleration, Delayed engagement when cold
Fix: ZF 5HP24 transmission cooler lines corrode at fittings; rubber transmission mounts collapse from age and heat. Cooler lines require dropping transmission pan for internal seals. Mount replacement is straightforward but tight access. 3-5 hours combined.
Estimated cost: $600-1,200
EVAP System and Fuel Filter Housing Leaks
Occasional · low severityTypical onset: any mileage
Symptoms: Check Engine Light with P0442/P0455 codes (EVAP leak), Fuel smell in cabin or near fuel tank, Failed emissions testing, Difficulty filling tank (pump clicks off repeatedly)
Fix: Plastic components in EVAP canister and fuel filter housing crack. Fuel filter lives under car near tank and isn't serviceable—whole assembly replaces. EVAP canister vent valve is common culprit. Related to recall for fuel system leaks. 2-4 hours depending on component.
Estimated cost: $400-900
Convertible Top Hydraulic System Failure (if Convertible)
Occasional · low severityTypical onset: any mileage, age-related
Symptoms: Top moves slowly or stops mid-cycle, Hydraulic fluid leaks in trunk, Grinding noise from hydraulic pump, Top won't latch or unlatch electrically
Fix: Hydraulic rams leak, pump motor fails, or microswitches misalign. System requires bleeding after any seal work. Common to replace pump and both rams preventively if one fails. 3-6 hours depending on extent.
Estimated cost: $1,200-2,500
Secondary Air Injection System Failure
Occasional · low severityTypical onset: 80,000-150,000 mi
Symptoms: Check Engine Light with P0410/P0411 codes, Rattling on cold start (pump bearing failure), Failed emissions test, Pump runs constantly or not at all
Fix: Air pump seizes or check valves fail. Only operates on cold start for emissions. Non-critical for operation but kills emissions testing. Pump replacement straightforward on firewall. 2-3 hours labor.
Estimated cost: $600-1,100
Front Suspension Lower Control Arm Bushings
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Clunking over bumps at low speed, Wandering on highway, Uneven tire wear on inside edges, Steering wheel off-center after alignment
Fix: Aluminum lower arms with pressed-in rubber bushings deteriorate. Arms aren't serviceable—full replacement required. Alignment mandatory after. 3-4 hours for both sides with alignment.
Estimated cost: $800-1,400
Buy only if Nikasil has been addressed or VIN confirms steel liners—otherwise you're buying a ticking time bomb that will grenade spectacularly.
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.