The 2002 Navigator shares the Ford Expedition platform with the 5.4L 2-valve Triton V8—a generally reliable truck engine marred by two catastrophic failures: spark plug threads stripping from aluminum heads and cam phaser/timing chain issues. Transmissions are robust but the cooling system integration causes premature failure.
Spark Plug Blowout / Stripped Cylinder Head Threads
Common · high severityTypical onset: 60,000-120,000 mi
Symptoms: sudden loss of power and loud hissing or popping from engine bay, misfire codes on one cylinder, spark plug literally shoots out of head during driving, compression loss on affected cylinder
Fix: Ford's 2-valve 5.4L used only 4 threads to hold spark plugs in soft aluminum heads. When they strip, you need thread repair inserts (TimeSert or HeliCoil). If multiple holes are damaged or head integrity is compromised, you're looking at head removal and machine work. Single plug blowout: 2-3 hours. Multiple or severe damage: 8-12 hours for heads-off repair.
Estimated cost: $500-1,200 per cylinder for insert repair, $2,500-4,000 if heads must come off
Timing Chain Tensioner and Cam Phaser Failure
Occasional · high severityTypical onset: 80,000-150,000 mi
Symptoms: loud rattling on cold start that quiets after 10-15 seconds, check engine light with cam/crank correlation codes, progressive loss of power, metallic chain slap that gets worse over time
Fix: The 2-valve Triton's plastic-backed tensioners fail and cam phasers seize or rattle. This requires front engine teardown: timing cover, chains, tensioners, guides, phasers, and oil pump drive. Often find metal contamination in oil pan requiring pan drop and flush. Book time 12-16 hours, mandatory to replace water pump and front seals while in there.
Estimated cost: $2,800-4,500
Transmission Cooler Line / Radiator Failure Leading to Trans Destruction
Common · high severityTypical onset: 70,000-130,000 mi
Symptoms: transmission slipping or delayed engagement, strawberry milkshake appearance in coolant reservoir (trans fluid mixing with coolant), overheating transmission, total trans failure if coolant enters valve body
Fix: The 4R100 transmission cooler is integrated into the radiator. When the internal barrier fails, coolant and ATF mix, destroying the transmission within miles. Requires radiator replacement, complete trans flush or rebuild, and all cooler lines. If caught early (just radiator): 3-4 hours. If trans contaminated: add 18-24 hours for rebuild.
Estimated cost: $800-1,200 for radiator and flush if caught immediately, $3,500-5,500 if transmission rebuild needed
Intake Manifold Coolant Crossover Leak
Common · medium severityTypical onset: 80,000-140,000 mi
Symptoms: coolant loss with no external leaks visible, sweet smell from engine bay, white smoke from exhaust on cold start, overheating in severe cases, coolant in valley between cylinder heads
Fix: Plastic coolant crossover passages in the intake manifold crack over time. Coolant leaks into the valley and sometimes into cylinders. Requires intake manifold removal, crossover replacement (go with aluminum aftermarket), new gaskets. 6-8 hours labor. While you're in there, replace thermostat and hoses.
Estimated cost: $1,200-1,800
Ball Joints and Control Arm Bushings
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: clunking over bumps, wandering steering, uneven tire wear on inside edges, steering wheel shimmy at highway speeds, failed state inspection
Fix: These 5,700-lb trucks eat front suspension components. Upper and lower ball joints wear out, control arm bushings crack. Most shops replace entire control arms with new bushings and joints pre-installed rather than pressing components. Front end typically needs 4-6 hours for both sides.
Estimated cost: $1,000-1,600 for full front suspension refresh
Rear Air Suspension Compressor and Air Spring Failure
Occasional · low severityTypical onset: 90,000-150,000 mi
Symptoms: rear sagging overnight or when parked, compressor runs constantly, suspension warning light, harsh ride over bumps, visible cracking on air spring bellows
Fix: Air springs develop leaks at folds, compressor seals fail, or dryer gets saturated. Can replace springs individually (2 hours each) or convert entire rear to coil springs with conversion kit (4-5 hours). Compressor replacement is 2-3 hours. Many owners opt for coil conversion to eliminate future air suspension headaches.
Estimated cost: $400-800 per air spring, $600-900 for compressor, $800-1,200 for full coil conversion
Fuel Pump Driver Module Failure
Occasional · medium severitySymptoms: no-start with crank but no fuel pump priming sound, stalling after running fine, intermittent starting issues, fuel pump runs continuously draining battery
Fix: Module mounted on frame rail near fuel tank controls pump operation. Solder joints crack from vibration or module overheats. Testing requires fuel pressure gauge and scanner. Replacement is straightforward: 1-1.5 hours. Located passenger side frame rail, often corroded fasteners add time.
Estimated cost: $300-500
Only if you're handy or have a trusted independent shop—these are comfortable highway cruisers when maintained, but the spark plug and transmission cooler issues are financially catastrophic for the unprepared buyer.
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.