The 2000 Mazda Millenia is a well-equipped luxury sedan let down by catastrophic engine failures on the 2.3L Miller-cycle supercharged (KJ-ZEM) engine and transmission weaknesses across both powertrains. The 2.5L V6 is significantly more reliable but transmission issues remain common.
2.3L Supercharged Engine Catastrophic Failure (Miller Cycle)
Common · high severityTypical onset: 80,000-130,000 mi
Symptoms: Severe rod knock or bottom-end noise, Loss of oil pressure, Metal shavings in oil, Sudden loss of power followed by engine seizure
Fix: Complete engine rebuild or replacement required. Connecting rod bearings fail due to inadequate oiling on this Miller-cycle design. Typical rebuild involves crank polishing/replacement, all bearings, piston rings, head gasket set. 25-35 hours labor for rebuild, 15-20 hours for used engine swap.
Estimated cost: $4,500-7,500
Automatic Transmission Failure (Both Engines)
Common · high severityTypical onset: 100,000-150,000 mi
Symptoms: Harsh shifting or slipping between gears, Delayed engagement from Park to Drive, Transmission overheating, Metal debris in transmission pan
Fix: The F4A-EL 4-speed automatic suffers clutch pack and valve body wear. Oil cooler lines also fail, leading to fluid contamination and accelerated wear. Rebuild requires 12-16 hours; replacement with used unit 8-10 hours. Always replace oil cooler during transmission work.
Estimated cost: $2,200-3,800
Supercharger Bearing and Seal Failure (2.3L Only)
Occasional · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Whining or grinding noise from supercharger on acceleration, Oil leaking from supercharger snout, Loss of boost pressure, Check engine light with lean codes
Fix: Lysholm-type supercharger requires bearing and seal replacement or complete unit replacement. Rebuild kits exist but labor-intensive. Remove and reinstall supercharger assembly. 8-12 hours labor.
Estimated cost: $1,800-3,200
Head Gasket Failure (Both Engines)
Occasional · high severityTypical onset: 110,000-160,000 mi
Symptoms: Coolant loss with no visible leak, White smoke from exhaust, Overheating under load, Oil contamination in coolant reservoir
Fix: Both cylinder heads must come off. Common on both V6 variants due to aluminum head/block interface. Includes head gasket set, timing components, coolant flush. Always check head flatness. 14-18 hours labor.
Estimated cost: $2,800-4,200
Transmission Oil Cooler Line Failure
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: Transmission fluid leak near radiator, Pink fluid pooling under front of vehicle, Low transmission fluid level, Transmission slipping after fluid loss
Fix: Steel lines rust through at bends and fittings. Replace both cooler lines and inspect external cooler. Can cause transmission failure if fluid loss goes unnoticed. 2-3 hours labor.
Estimated cost: $350-650
Crank Position Sensor Failure
Occasional · high severityTypical onset: 80,000-150,000 mi
Symptoms: No-start condition with no crank reference, Intermittent stalling while driving, Engine cranks but won't fire, Tachometer drops to zero while running
Fix: Sensor located behind timing cover on some variants, easier access on others. Heat cycles cause internal failure. 1.5-3 hours labor depending on engine variant and accessibility.
Estimated cost: $250-550
Skip the 2.3L supercharged model entirely unless the engine has already been rebuilt with receipts; the 2.5L is a safer bet but still expect transmission work before 150,000 miles.
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.