The 1999 Explorer is notorious for catastrophic timing chain failures on SOHC engines and transmission self-destruction, making it one of Ford's riskier mid-size SUVs from this era. The 4.0L OHV is more durable but underpowered; the 5.0L V8 is rare but generally solid.
4.0L SOHC Timing Chain Cassette Failure
Common · high severityTypical onset: 80,000-150,000 mi
Symptoms: Rattling noise on cold start that quiets after warmup, Check engine light with cam/crank correlation codes, Sudden catastrophic engine failure with metal shavings in oil, Loss of power and rough running
Fix: SOHC engines use plastic-backed timing chain cassettes that disintegrate. Plastic shards circulate through the engine, often destroying bearings and requiring full rebuild or replacement. Preventive cassette replacement is 12-15 hours labor; post-failure rebuild is 25-35 hours. Many shops won't touch the preventive job due to liability.
Estimated cost: $2,500-4,000 preventive; $4,500-7,500 engine rebuild/replacement
5R55E Transmission Failure
Common · high severityTypical onset: 90,000-140,000 mi
Symptoms: Harsh 2-3 or 3-4 shifts, Slipping between gears under load, No reverse or delayed engagement, Burnt transmission fluid smell, Metal shavings in pan during service
Fix: The 5R55E is fundamentally weak, with coast clutch and overdrive servo failures being epidemic. Band adjustments and fluid changes rarely save it once symptoms appear. Expect rebuild (18-22 hours) or replacement. Cooler line corrosion (per recalls) accelerates failure.
Estimated cost: $2,200-3,800
Front Ball Joint Separation
Common · high severityTypical onset: 70,000-120,000 mi
Symptoms: Clunking over bumps, Wandering steering, Uneven tire wear on inside edges, Visible grease boot tears, In catastrophic cases: sudden loss of steering control
Fix: Lower ball joints wear and can separate from the knuckle without warning—this was a major safety issue across early 2000s Explorers. Both sides should be done simultaneously (4-6 hours). Some techs replace entire control arms for liability reasons, adding cost.
Estimated cost: $600-1,200
Rear Axle Bearing and Seal Leaks
Common · medium severityTypical onset: 80,000-130,000 mi
Symptoms: Gear oil dripping inside rear brake drums, Rear brake contamination and reduced stopping, Howling noise from rear that changes with speed, Visible oil on inside of wheel
Fix: Axle seals fail and allow gear oil to contaminate rear drum brakes. Requires axle removal, seal replacement, and brake overhaul on affected side (3-4 hours per side). If bearing is damaged, add bearing replacement time.
Estimated cost: $400-800 per side
Intake Manifold Gasket Coolant Leaks (SOHC)
Occasional · medium severityTypical onset: 100,000-160,000 mi
Symptoms: Coolant smell from engine bay, Slow coolant loss without visible external leaks, White smoke on cold start, Rough idle when engine is cold
Fix: The plastic intake manifold warps and gaskets fail, allowing coolant into cylinders or external leaks. Replacement requires removing upper plenum and runners (6-8 hours). Use OEM gaskets—aftermarket versions often fail quickly.
Estimated cost: $800-1,400
Cruise Control Deactivation Switch Fire Risk
Occasional · high severitySymptoms: Burning smell from under hood near brake master cylinder, Smoke from engine bay, Cruise control stops working, Melted wiring near brake pedal assembly
Fix: Speed control deactivator switch can short and cause under-hood fires even with ignition off (multiple recalls). Check if recalls 00S05, 04E024, or 06S05 were completed. Replacement is 1-2 hours if not recalled.
Estimated cost: $150-300 if not covered by recall
EVAP Purge Valve and Vacuum Leak Issues
Common · low severityTypical onset: 60,000-110,000 mi
Symptoms: Check engine light with P0442, P0443, P0455 codes, Rough idle, Fuel smell, Failed emissions testing
Fix: Vacuum lines become brittle, and the EVAP canister purge valve sticks. Diagnosis involves smoke testing (1 hour), then replacing valve and damaged vacuum lines (1-2 hours total).
Estimated cost: $200-450
Hard pass unless it's an OHV 4.0L with verified maintenance records and under $3,000—the SOHC engine and 5R55E transmission are ticking time bombs that often cost more to fix than the vehicle is worth.
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.