The 2000 Lincoln Navigator with the 5.4L 2-valve Triton V8 is a capable luxury SUV undermined by catastrophic spark plug ejection issues and transmission cooling failures. When the engine stays together, it's a solid truck; when it doesn't, you're looking at a complete rebuild.
Spark Plug Ejection / Stripped Threads (Cylinder Head Failure)
Common · high severityTypical onset: 60,000-150,000 mi
Symptoms: Sudden loud popping or hissing sound from engine bay, Immediate loss of power and rough running, Check engine light with misfire codes, Visible spark plug and coil blown out of cylinder head
Fix: The 2-valve 5.4L has inadequate spark plug thread engagement (4 threads vs. 8+ on most engines). Plugs blow out under combustion pressure, stripping aluminum threads. If caught early, a HeliCoil or TimeSert thread repair kit runs 2-3 hours per hole. If multiple cylinders are affected or threads are destroyed, you're looking at cylinder head removal (8-12 hours) or complete engine replacement. Many techs won't guarantee thread repairs long-term.
Estimated cost: $500-1,200 per cylinder for insert repair; $4,000-8,000 for heads-off repair or short block
Transmission Oil Cooler Line Failure (Internal to Radiator)
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: Transmission slipping or delayed engagement, Milky or strawberry-colored transmission fluid, Coolant in transmission pan or radiator, Overheating transmission and engine simultaneously
Fix: The transmission cooler built into the radiator develops internal leaks, allowing coolant and ATF to mix. This contamination destroys the 4R100 transmission within days if not caught immediately. Proper fix requires new radiator with external transmission cooler, complete transmission flush or rebuild, and all cooler lines replaced. If driven after mixing fluids, expect full transmission rebuild (12-16 hours). This is a known design flaw across Ford trucks of this era.
Estimated cost: $800-1,500 preventive (radiator + lines + flush); $3,000-4,500 after transmission damage
Intake Manifold Coolant Crossover Leak
Common · medium severityTypical onset: 70,000-130,000 mi
Symptoms: Coolant smell in cabin when heat is on, Visible coolant seepage at front of intake manifold, Slow coolant loss with no external leaks visible, White steam from exhaust on cold starts (if severe)
Fix: Plastic coolant crossover passages in the intake manifold crack or the gaskets fail, leaking coolant into the valley or intake ports. Requires upper intake removal to replace crossover tubes and gaskets (4-6 hours). Ford released updated metal crossover kits. If coolant gets into cylinders, you risk hydrolock or bearing damage. Must pressure-test cooling system regularly.
Estimated cost: $600-1,200
4R100 Transmission Overdrive Band Failure
Occasional · medium severityTypical onset: 100,000-180,000 mi
Symptoms: Slipping or flare on 3-4 upshift, No overdrive or falls out of overdrive under load, Harsh downshifts from 4th gear, Transmission overheating on highway
Fix: The overdrive band adjusts or wears out, especially if fluid service was neglected. Adjustment is external and takes 30 minutes, but if the band is glazed or broken, the transmission needs to come out for internal service (8-10 hours R&R plus rebuild time). The 4R100 is generally robust but demands fresh Mercon V fluid every 30-40k miles in truck service.
Estimated cost: $150-250 for adjustment; $2,200-3,500 for rebuild
Front Suspension Ball Joint Failure
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Clunking or popping from front end over bumps, Wandering or loose steering feel, Uneven tire wear on inside edges, Visible play in wheel when prying tire at 12 and 6 o'clock
Fix: Upper and lower ball joints wear out, especially uppers. These are not greaseable on most applications. Failure can cause wheel separation. Requires replacing entire control arms in many cases since Ford pressed in non-serviceable joints. Both sides typically need work at similar mileage. Plan on alignment afterward. Budget 3-5 hours for both sides.
Estimated cost: $800-1,400 for both sides with arms
Rear Air Suspension Compressor and Bag Failure
Occasional · low severityTypical onset: 90,000-150,000 mi
Symptoms: Rear sags overnight or after sitting, Compressor runs constantly or not at all, Suspension warning light illuminated, Uneven ride height side-to-side
Fix: Air springs crack or leak at the folds, and the compressor wears out from overwork. Many owners convert to coil springs (2-3 hours, $300-500 in parts) rather than replace air components. OEM air spring replacement is 1.5-2 hours per side; compressor is another 2 hours. Air system adds complexity without much benefit unless you tow heavy regularly.
Estimated cost: $600-900 per air spring; $500-800 for compressor; $400-700 for coil conversion kit installed
Fuel Pump Driver Module Failure
Occasional · medium severitySymptoms: Intermittent stalling or no-start when hot, Fuel pump not priming (no hum from tank), Dies while driving, restarts after cooling, No fuel pressure at rail
Fix: The fuel pump driver module (FPDM) mounted on the frame rail near the fuel tank fails due to heat and corrosion. It controls pump speed via PWM signal. When it fails, pump doesn't run. Module replacement is straightforward (1 hour) but diagnosis can be tricky if intermittent. Ford had a TSB on this. Clean connections and check for corrosion.
Estimated cost: $250-450
Only buy if you can verify the spark plugs have been properly serviced and the radiator/trans cooler have been addressed; otherwise, you're gambling on a $6,000 engine or transmission failure with every mile.
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.