The 1965 Mercury Comet shares its platform with the Ford Falcon and represents a transitional year before the larger '66 redesign. Most survivors today run the bulletproof 200ci I6 or 289ci V8, though big-block swaps complicate things. These are simple, body-on-frame cars where mechanical issues rarely strand you, but 60-year-old components and rust are your real enemies.
Timing Chain Stretch and Gear Wear (I6 and Small-Block V8)
Common · medium severityTypical onset: 80,000+ mi (or unknown history)
Symptoms: Hard starting when warm, excessive cranking, Erratic idle and backfiring through carburetor, Rattling noise from front of engine on cold start, Ignition timing drifts despite repeated adjustments
Fix: Replace timing chain, gears, and tensioner as a set. 200ci I6 takes 3-4 hours; 289 V8 takes 4-5 hours due to tighter engine bay. Must remove radiator, water pump, harmonic balancer, and front cover. Critical to verify cam gear hasn't worn excessively or chewed up the cam snout. Most use double-roller chains now for longevity.
Estimated cost: $450-850
Manual Steering Box Slop and Wandering
Common · medium severitySymptoms: Excessive play at steering wheel (more than 2 inches), Car wanders lane to lane on highway, Clunking when reversing steering input, Front end feels vague and unresponsive
Fix: Original Ford manual steering boxes wear internally and adjustment only helps temporarily. Rebuild kits exist but labor-intensive (5-6 hours including alignment). Most shops recommend remanufactured box swap (2-3 hours). Verify idler arm and tie rod ends aren't also shot before diagnosing box. Power steering cars less common but have separate leak/pump issues.
Estimated cost: $400-750
Generator-to-Alternator Conversion Issues
Occasional · medium severitySymptoms: Dim headlights at idle, brightening with RPM, Battery slowly discharges during short trips, Ammeter shows discharge under electrical load, No-start after sitting, weak cranking
Fix: Many '65 Comets still run original generators (35-40 amp max). Modern electrical accessories overload them. Proper alternator conversion requires correct pulley, brackets, voltage regulator swap (external to internal), and wiring changes. Half-done conversions cause weird charging behavior. Takes 2-3 hours to do correctly. Verify voltage regulator is matched to alternator type.
Estimated cost: $350-600
Rear Axle Seals and Pinion Seal Leaks
Common · low severityTypical onset: 60,000+ mi
Symptoms: Gear oil dripping on inside of brake drums, Oil spots on garage floor behind rear wheels, Reduced braking effectiveness on one rear wheel, Visible oil seepage at pinion yoke
Fix: Original neoprene seals harden with age. Axle seals require backing off axle bearings and pulling shafts (1.5-2 hours per side). Pinion seal requires driveshaft removal, pinion nut removal, yoke puller (2-3 hours). Critical to mark pinion depth before disassembly. Contaminated rear brake shoes must be replaced ($80-120 additional). Often find worn wheel bearings during this job.
Estimated cost: $300-650
Floor Pan and Torque Box Rust Perforation
Common · high severitySymptoms: Visible rust holes in driver/passenger floor under carpet, Sagging rear seat floor, visible ground underneath, Cracking or separation at rear spring mounts (torque boxes), Car feels flexy over bumps, clunking from rear suspension
Fix: Unibody design concentrates stress at torque boxes where rear leaf springs mount. These rust from inside out. Floor pans rust from water intrusion through cowl or door seals. Proper repair requires cutting out rot, welding in replacement panels (20-40 hours depending on severity). Patch panels available but quality varies. Rear torque box failure affects structural integrity and suspension geometry. This is the car-killer for northern survivors.
Estimated cost: $2,500-6,500
Single-Bowl Carburetor Stumble and Bog (200ci I6)
Occasional · low severitySymptoms: Hesitation or stumble on acceleration from stop, Bogging when pressing throttle quickly, Black smoke when cold, lean surge when hot, Hard to tune for both idle and performance
Fix: 200ci engines used Autolite 1100 or Holley 1904 single-barrel carbs. Accelerator pump diaphragms harden, power valves stick, float needles wear. Rebuild kits are $30-50 but ethanol fuel damages aged components. Takes 2-3 hours to rebuild on-car if familiar. Many owners swap to Weber 32/36 DGEV conversion ($300-400) for 2-barrel performance and reliability (4-5 hours with manifold adapter fabrication).
Estimated cost: $150-450
Buy one if the body is solid and you can verify mechanical history—drivetrain parts are cheap and available, but rust repair costs more than the car's worth.
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.