The 2009 Lincoln MKS with the 3.7L Duratec V6 is a comfortable FWD/AWD luxury sedan built on Ford's D3 platform, but it suffers from catastrophic engine failures tied to carbon buildup on direct-injection internals and a transmission cooling defect that can grenade the 6F50/55 six-speed automatic.
Direct-Injection Carbon Buildup Leading to Engine Failure
Common · high severityTypical onset: 80,000-130,000 mi
Symptoms: Rough idle, misfires, CEL for lean codes or multiple misfires, Loss of power on acceleration, hesitation, Ticking or rattling from valve train at cold start, Excessive oil consumption (1 qt per 1,000 mi or worse), Catastrophic failure: spun bearings, scored cylinder walls, broken ringlands
Fix: Early stage: walnut-blast intake valves every 40k-50k ($400-700, 3-4 hours). Advanced stage with damage: short block or complete engine rebuild required. Includes new pistons, rings, bearings, possibly head work. 20-30 labor hours for a full rebuild.
Estimated cost: $6,000-10,000
Transmission Oil Cooler Internal Leak (Coolant-to-Trans Fluid)
Common · high severityTypical onset: 70,000-110,000 mi
Symptoms: Transmission slipping, delayed or harsh shifts, Milky or strawberry-colored transmission fluid (coolant contamination), Engine overheating or coolant loss with no external leaks, Transmission failure if not caught early
Fix: Replace transmission oil cooler and flush/replace all contaminated fluid. If contamination reached the trans, a full rebuild or replacement is required (12-16 hours). External cooler install recommended to prevent repeat.
Estimated cost: $800-1,200 (cooler only) or $3,500-5,500 (with trans rebuild/replacement)
Piston Ring Failures and Bore Scoring
Occasional · high severityTypical onset: 90,000-140,000 mi
Symptoms: Excessive oil consumption requiring frequent top-ups, Blue smoke from exhaust on startup or under load, Loss of compression, poor performance, Metallic knocking or rattling under acceleration
Fix: Requires engine disassembly, cylinder honing or boring (if scored), new pistons and rings. Often combined with bearing replacement. 18-25 labor hours for proper rebuild.
Estimated cost: $5,000-8,500
PTU (Power Transfer Unit) Failure on AWD Models
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Grinding, whining, or clunking from the front of vehicle during turns, Binding sensation in tight turns, Loss of AWD functionality, AWD warning light, Fluid leaking from PTU (mounted on transmission)
Fix: PTU shares fluid with transmission but runs hot and breaks down fluid. Replace PTU unit (requires trans removal or drop, 8-12 hours). Preventive fluid changes every 30k can help but not always effective.
Estimated cost: $2,000-3,200
Timing Chain Stretch and Phaser Failure
Occasional · high severityTypical onset: 100,000-150,000 mi
Symptoms: Rattling noise from front of engine at cold start (goes away when warm), CEL for cam/crank correlation codes (P0016, P0017, P0018), Rough running, poor fuel economy, In severe cases, timing jump causing valve-to-piston contact
Fix: Replace timing chains (primary and secondary), guides, tensioners, and variable cam timing (VCT) phasers. Front engine tear-down required. 12-16 labor hours.
Estimated cost: $2,800-4,200
Water Pump Failure
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Coolant leaks from front of engine (weep hole on pump), Squealing or grinding noise from accessory belt area, Engine overheating, temperature gauge climbing, Coolant smell or visible drips under vehicle
Fix: Replace water pump and thermostat while in there. Mechanical pump driven by accessory belt (easier than timing-chain-driven). 3-4 labor hours.
Estimated cost: $600-900
Transmission Mounts Collapsing
Common · low severityTypical onset: 70,000-110,000 mi
Symptoms: Clunking on acceleration or deceleration, Excessive engine/trans movement visible when shifting into drive or reverse, Vibration through cabin at idle or under load
Fix: Replace motor and transmission mounts. Usually all three should be done together. 2-3 labor hours.
Estimated cost: $400-700
Hard pass unless under 60k miles with full service records showing religious preventive carbon cleaning, fluid changes, and no trans cooler contamination history—otherwise you're buying someone else's expensive engine or transmission failure.
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.