The 720S is McLaren's M840T twin-turbo V8 masterpiece, but early examples suffer from catastrophic engine failures due to piston ring and bore wear, plus hydraulic actuation system headaches. When properly maintained and unaffected by the 'piston recall,' these are incredible machines—but the engine lottery is real.
Piston Ring / Cylinder Bore Failure (M840T Engine)
Occasional · high severityTypical onset: 15,000-40,000 mi
Symptoms: Excessive oil consumption (1+ qt per 1,000 mi), Blue smoke on cold start or hard acceleration, Low compression readings on one or more cylinders, Check engine light with misfire codes (P0300-P0308)
Fix: Complete engine rebuild or short-block replacement. McLaren issued a Technical Service Bulletin and extended warranty coverage for affected VINs, but many early cars weren't caught. Proper fix requires removing body panels, engine out, bore honing or replacement, new pistons/rings, gaskets. 60-80 labor hours at a McLaren-certified shop.
Estimated cost: $35,000-65,000
Hydraulic Lift System Failure
Common · medium severitySymptoms: Front axle lift won't raise or gets stuck mid-travel, Hydraulic pump runs constantly or makes whining noise, Fluid leaks near front strut towers or under center tunnel, Dashboard warning: 'Hydraulic Fault' or 'Lift Unavailable'
Fix: Usually the hydraulic pump or accumulator. Pump replacement requires partial undertray removal and bleeding the system. Leaking lines or actuators add time. 4-8 hours depending on which component fails.
Estimated cost: $3,500-7,500
Transmission Oil Cooler Leaks
Occasional · medium severityTypical onset: 30,000-60,000 mi
Symptoms: Transmission fluid dripping from undertray center section, Low transmission fluid warning on dash, Harsh or delayed shifts when fluid level drops, Visible oil pooling after car sits overnight
Fix: Oil cooler O-rings degrade or cooler itself cracks. Requires removing belly panels and some hydraulic lines for access. Replace cooler and lines, refill/bleed SSG transmission. 6-10 hours.
Estimated cost: $2,800-5,000
Fuel Tank Recall & Evap System Issues
Common · high severitySymptoms: Strong fuel smell in cabin or near rear of car, Check engine light with EVAP leak codes (P0442, P0456), Fuel gauge erratic or stuck, Difficulty fueling / pump clicks off prematurely
Fix: NHTSA recall 19V-383 addressed fuel tank cracking. If already done, watch for EVAP canister and vent valve failures. Tank replacement requires body lift or partial rear clamshell removal. 12-18 hours if not warranty.
Estimated cost: $8,000-15,000
Transmission Mounts Deteriorating
Occasional · low severityTypical onset: 40,000-70,000 mi
Symptoms: Clunking or thudding on hard acceleration or downshifts, Excessive driveline vibration at idle in gear, Visible sagging or torn rubber in transmission mounts
Fix: The 7-speed SSG sits in a carbon tub cradle. Mounts fatigue from heat and torque cycling. Requires lift, undertray removal, and supporting transmission. 5-7 hours for both mounts.
Estimated cost: $2,200-3,800
Infotainment / IRIS System Glitches
Common · low severitySymptoms: Touchscreen freezes or restarts randomly, Bluetooth won't pair or drops constantly, Backup camera black screen or distorted, Climate control unresponsive via screen
Fix: Software updates often resolve issues, but some cars need full IRIS module replacement. Dealer-only programming. 1-2 hours for reflash, 3-4 if module swap needed.
Estimated cost: $500-2,500
Buy only with comprehensive pre-purchase inspection and confirmed piston TSB completion—right car is transcendent, wrong one is a $50k engine rebuild waiting to happen.
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.