The 2020 Z4 M40i shares the Toyota Supra platform and B58 engine—generally solid, but early G29 chassis examples saw transmission cooling issues and some catastrophic B58 bearing failures tied to low-speed pre-ignition (LSPI) on tune-happy cars or neglected oil changes.
Transmission Oil Cooler Failure / Leaking
Occasional · medium severityTypical onset: 30,000-60,000 mi
Symptoms: Transmission fluid puddle under car, often pink/red staining, Harsh shifting or delayed engagement when fluid is low, Check engine light with transmission overtemp codes
Fix: Replace cooler and lines, flush system. 3-4 hours labor. Common on early ZF 8HP models; revised part available.
Estimated cost: $800-1,400
B58 Connecting Rod Bearing Wear / Spun Bearing
Rare · high severityTypical onset: 40,000-80,000 mi
Symptoms: Knocking or ticking noise on cold start that doesn't go away, Sudden loss of oil pressure, engine warning light, Metallic debris in oil during change
Fix: Full engine rebuild or short-block replacement. 20-30 hours labor depending on extent. Worst-case scenario if LSPI event occurs or extended oil change intervals. Not widespread but catastrophic when it happens.
Estimated cost: $8,000-15,000
Transmission Mount Failure
Common · low severityTypical onset: 50,000-90,000 mi
Symptoms: Clunking when shifting into drive or reverse, Excessive drivetrain movement felt through chassis, Vibration at idle in gear
Fix: Replace trans mount. 1.5-2 hours labor. Hydraulic mount design degrades faster with spirited driving.
Estimated cost: $400-700
High-Pressure Fuel Pump (HPFP) Failure
Occasional · high severitySymptoms: Long crank / no-start condition, Rough idle, misfires under load, Fuel pressure fault codes, limp mode
Fix: Replace HPFP on intake side of engine. 2-3 hours labor. Some B58s got updated pump design; failure often tied to bad fuel or contamination.
Estimated cost: $1,200-2,000
Coolant Thermostat / Housing Leaks
Occasional · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Coolant weeping from front of engine, Overheating or slow warm-up, Sweet smell after driving
Fix: Replace thermostat and housing assembly. 2-3 hours labor. Plastic housing fatigues; do water pump at same time if high mileage.
Estimated cost: $600-1,100
Soft-Top Mechanism Binding / Motor Failure
Occasional · low severitySymptoms: Roof stops mid-cycle, error message on dash, Grinding or clicking noise during operation, Manual release required to close/open
Fix: Lubricate rails and pivots; replace motor or microswitch if mechanical failure. 1-3 hours labor depending on component. Keep drains clear to avoid water intrusion.
Estimated cost: $300-1,500
Buy a 2020+ with full service records and confirm no tuning history—solid platform if maintained, but bearing failures and trans cooler issues make a pre-purchase inspection with oil analysis mandatory.
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.