The 2015 Q70L is Infiniti's long-wheelbase luxury sedan on the proven Y51 platform. The 3.7L VQ37VHR is generally reliable, but the 5.6L VK56VD V8 has catastrophic oil-consumption issues that can grenade motors. Transmission cooler failures and driveline vibrations are platform-wide concerns.
5.6L V8 Catastrophic Oil Consumption & Engine Failure
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Burning 1+ quart per 1,000 miles with no visible leaks, Blue smoke on startup or acceleration, Check engine light for multiple misfires, Complete engine seizure if oil starvation occurs
Fix: Piston ring land failure allows oil into combustion chambers. No partial fix exists—requires complete engine rebuild (40-50 hours) or replacement long block (25-30 hours). Many owners discover this too late after catastrophic failure.
Estimated cost: $12,000-18,000
Transmission Oil Cooler Failure (7AT)
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Transmission fluid in coolant or coolant in transmission (strawberry milkshake fluid), Transmission slipping or delayed engagement, Overheating transmission temp warnings, Catastrophic transmission failure if cross-contamination occurs
Fix: Internal cooler in radiator fails, allowing fluid cross-contamination. Requires radiator replacement, full transmission flush or rebuild if contaminated (trans rebuild adds 18-22 hours). Radiator alone is 3-4 hours. If you catch it early (cooler only), much cheaper.
Estimated cost: $800-1,200 (cooler only), $4,500-7,000 (with transmission rebuild)
Driveshaft Center Support Bearing Failure (AWD)
Occasional · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Clunking or vibration at 30-50 mph during acceleration, Droning or humming from underneath vehicle, Vibration worsens under load or when cold, Related to NHTSA recall for driveshaft issues
Fix: Center support bearing and flex disc wear out. Driveshaft removal and bearing/coupling replacement takes 4-5 hours. Some techs replace entire driveshaft assembly to avoid comebacks. Check for related recall coverage first.
Estimated cost: $800-1,400
Transmission Mount Collapse
Common · medium severityTypical onset: 60,000-90,000 mi
Symptoms: Clunk when shifting from Park to Drive or Reverse, Excessive vibration at idle in gear, Visible engine/trans movement when revving in Park
Fix: Hydraulic transmission mount deteriorates, especially on V8 models due to torque. Replacement is straightforward, 2-3 hours including subframe support. OEM mount strongly recommended over aftermarket.
Estimated cost: $450-750
Fuel System Clogging & Filter Issues
Occasional · medium severityTypical onset: 90,000-130,000 mi
Symptoms: Hard starting after sitting overnight, Hesitation or stumble under acceleration, Intermittent stalling, usually when fuel level is low, Check engine light for fuel trim codes
Fix: In-tank fuel filter/strainer clogs from debris or fuel pump sock deterioration. Requires fuel tank drop (4-5 hours). Often find corroded fuel level sender at same time. Replace pump assembly while you're in there.
Estimated cost: $900-1,500
3.7L VQ37 Timing Chain Rattle (Gallery Gasket)
Occasional · medium severityTypical onset: 100,000-140,000 mi
Symptoms: Rattling noise from front of engine on cold start for 2-5 seconds, Noise disappears once oil pressure builds, May trigger cam timing codes if severe
Fix: Oil gallery gaskets leak, delaying oil pressure to timing chain tensioners. Requires front cover removal, timing chain inspection, and gasket replacement (12-15 hours). Not as common as older VQ engines but still occurs. Check oil pressure at startup before condemning.
Estimated cost: $2,200-3,500
The 3.7L V6 model is a solid luxury cruiser if maintained; avoid the 5.6L V8 entirely unless you have records proving no oil consumption and budget for a potential engine replacement.
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.