The 2019 McLaren 720S is a remarkable supercar with the M840T twin-turbo V8, but it carries significant mechanical fragility particularly in the engine internals and hydraulics. These are not high-mileage commuter issues—many catastrophic failures occur well before 30,000 miles due to manufacturing inconsistencies and aggressive heat cycling.
Catastrophic Engine Failure (Piston/Bearing/Rod Knock)
Occasional · high severityTypical onset: 5,000-35,000 mi
Symptoms: Metallic knocking from engine bay at idle or under load, Low oil pressure warning, Metal shavings in oil during analysis, Sudden loss of power, Check engine light with misfire codes
Fix: Complete engine rebuild or short block replacement required. This involves dropping the entire powertrain (8-12 hours alone), disassembly, machining, and reinstallation. Main bearings, rod bearings, pistons, rings commonly replaced together. Some cases require full crankshaft replacement. Total job runs 60-100 shop hours depending on collateral damage. Parts availability can delay repairs 4-8 weeks.
Estimated cost: $45,000-85,000
Dual-Clutch Transmission Oil Cooler Failure
Common · high severityTypical onset: 15,000-40,000 mi
Symptoms: Transmission overheat warnings on display, Harsh or delayed shifts especially when hot, Transmission fluid leaking from bell housing area, Limp mode activation, Burning smell after spirited driving
Fix: Oil cooler lines crack or cooler core itself fails, contaminating trans fluid and causing overheating. Requires dropping transmission (18-24 hours), replacing cooler assembly, flushing system, new fluid, and often replacing clutch packs if contamination occurred. Transmission mounts typically replaced during this service as they fatigue from heat.
Estimated cost: $12,000-22,000
Hydraulic Brake Line Corrosion and Failure
Occasional · high severitySymptoms: Spongy brake pedal feel, Brake fluid leaks visible near wheels or under car, Brake warning light, Pedal going to floor, Uneven braking or pulling to one side
Fix: Stainless brake lines can corrode at fittings due to road salt or moisture—this triggered a recall but failures still occur outside recall scope. All four corners typically need line replacement as preventive measure once one fails. Bleeding system, pressure testing required. 6-10 hours labor depending on how many lines replaced.
Estimated cost: $3,500-6,500
Head Gasket Failure
Occasional · high severityTypical onset: 20,000-50,000 mi
Symptoms: White smoke from exhaust on startup, Coolant loss with no visible leaks, Oil milky/chocolate color on dipstick, Overheating under load, Rough idle or misfires, Sweet smell from exhaust
Fix: M840T runs extremely hot and head gasket failures occur more frequently than expected. Both heads typically done together (penny-wise/pound-foolish to do one). Requires engine-out service, head resurfacing, ARP stud upgrade recommended. 40-55 hours total with proper cleanup and retorque procedure.
Estimated cost: $28,000-42,000
Fuel System Contamination/Filter Clogging
Occasional · medium severityTypical onset: 10,000-30,000 mi
Symptoms: Hesitation or stumbling on acceleration, Difficulty starting when hot, Fuel system pressure faults, Limp mode, Engine cutting out at high RPM
Fix: Fuel tank assembly issues (subject of recall) plus high-pressure fuel pump sensitivity means filters clog prematurely or tank debris circulates. Fuel filter replacement requires dropping tank (4-6 hours). If pump contaminated, add another $3K-5K. Always replace fuel filters and inspect tank during any fuel system work.
Estimated cost: $2,200-7,500
Shift Solenoid Pack Failures
Occasional · medium severityTypical onset: 25,000-60,000 mi
Symptoms: Harsh or delayed shifts between specific gears, Transmission fault codes, Stuck in one gear, Flashing transmission warning light, Erratic shift behavior in manual mode
Fix: SST dual-clutch uses complex solenoid pack for hydraulic actuation. Individual solenoids fail but best practice is replacing entire pack. Trans must come out (18-22 hours), mechatronic unit disassembly, solenoid pack replacement, adaptation procedure. Often discovered during oil cooler repairs.
Estimated cost: $8,500-14,000
Buy only with comprehensive warranty and a $20K repair reserve—these are financially devastating when they break, and they will break, often spectacularly and early.
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.