The NB2-generation Miata (2001-2005) with the 1.8L BP engine is generally bulletproof, but a few specific weaknesses show up at higher mileage: oil consumption from worn piston rings, short-nosed crankshaft failures, and transmission mount deterioration. Most examples are well-maintained by enthusiasts, but track cars and those with deferred maintenance can need major engine work.
Piston Ring Wear / Oil Consumption
Common · medium severityTypical onset: 100,000-150,000 mi
Symptoms: Burning a quart of oil every 500-1,000 miles, Blue smoke on cold starts or deceleration, Fouled spark plugs on cylinders 3 and 4 especially
Fix: Requires engine teardown to replace piston rings and oftenpistons if ring lands are damaged. Can be done in-chassis but most shops pull the engine for access. 16-20 hours labor for full ring job with honing and cleanup.
Estimated cost: $2,200-3,800
Short-Nose Crankshaft Failure (Woodruff Key Shear)
Occasional · high severityTypical onset: 80,000-140,000 mi
Symptoms: Sudden rattling or knocking from front of engine, Crank pulley wobble visible at idle, Check engine light with cam/crank correlation codes, Total loss of spark and fuel sync if key fully shears
Fix: The factory Woodruff key on the crankshaft nose can shear, especially if the crank bolt was ever improperly torqued. Requires crank removal, keyway repair or crankshaft replacement, and timing belt service. 12-18 hours labor depending on crank condition. Many shops install an oversized key or pin the pulley.
Estimated cost: $1,800-4,500
Rear Main Seal / Oil Pan Gasket Leaks
Common · low severityTypical onset: 120,000+ mi
Symptoms: Oil drips on garage floor after overnight parking, Visible oil weepage at engine/trans bellhousing junction, Oil residue along bottom of clutch dust cover
Fix: Rear main seal requires transmission removal. Oil pan gasket is easier but often done together. 6-8 hours for rear main with trans out, add 2 hours if doing pan gasket simultaneously. Good time to replace clutch if original.
Estimated cost: $900-1,600
Transmission Mount Collapse
Common · low severityTypical onset: 80,000-120,000 mi
Symptoms: Clunking on shifts, especially 1st to 2nd, Excessive shifter vibration at idle, Visible sag or torn rubber on mount beneath transmission
Fix: The rubber transmission mount (PPF mount) deteriorates and causes driveline slop. Replacement is straightforward: raise car, support trans, swap mount. 1.5 hours labor. Poly aftermarket mounts last longer but transmit more NVH.
Estimated cost: $180-350
Valve Cover Gasket / Spark Plug Tube Seal Leaks
Occasional · low severityTypical onset: 90,000+ mi
Symptoms: Oil pooling in spark plug wells, causing misfires, Burning oil smell from exhaust manifold area, Oil residue along valve cover perimeter
Fix: Valve cover gasket set includes plug tube seals. Straightforward job: remove coil packs, valve cover, clean surfaces, install new gasket and seals. 2-3 hours labor. Use OEM Mazda gasket for best longevity.
Estimated cost: $280-500
Cam Angle Sensor (CAS) Failure
Occasional · high severitySymptoms: No-start condition with cranking but no spark, Intermittent stalling at idle or when hot, Check engine light with crank position sensor code
Fix: The cam angle sensor in the distributor fails internally. Replacement distributor or CAS assembly is required. 1.5 hours labor. OEM part recommended; aftermarket sensors have high failure rates. Common issue on cars stored outdoors in humid climates.
Estimated cost: $350-650
Excellent used buy if maintenance records show regular oil changes and timing belt service—most engine work stems from neglect or track abuse, not design flaws.
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.