The 1982 Cadillac Seville represents a transitional year with three engine options—two of which are notorious problem children. The 350 diesel and especially the 4.1L V8-6-4 variable displacement gasoline engine have earned legendary status for catastrophic failures, while the 368 V8 is relatively solid but thirsty.
4.1L V8-6-4 Cylinder Deactivation System Failure
Common · high severityTypical onset: 40,000-80,000 mi
Symptoms: Rough idle and stalling when cylinders stick deactivated, Check engine light with solenoid codes, Poor fuel economy defeating the system's purpose, Eventually leads to burnt valves and worn camshaft lobes from oil starvation
Fix: Most techs disable the system entirely (4-6 hours) by installing a bypass kit and reprogramming the ECM. If internal damage occurred, expect head work or full engine rebuild (25-35 hours). Many owners swap to a traditional 368 or Chevy 350.
Estimated cost: $800-1,200 for disable kit, $4,500-7,500 for rebuild
350 Diesel Engine Catastrophic Failure
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Head gasket failures with coolant in oil (milky dipstick), Cracked cylinder heads from insufficient head bolt torque, Main bearing failures leading to spun bearings, Sudden loss of compression across multiple cylinders
Fix: The Oldsmobile 350 diesel has inadequate head bolts and block casting for diesel pressures. Head gasket jobs (18-22 hours) often reveal cracked heads. Full rebuilds (30-40 hours) are common, but most opt for a gas engine swap instead given parts scarcity and repeat failures.
Estimated cost: $5,000-8,000 rebuild, $4,000-6,000 for gas engine swap
THM 325-4L Overdrive Transmission Failures
Common · high severityTypical onset: 80,000-130,000 mi
Symptoms: Overdrive unit burns up causing no 4th gear, Slipping between 2nd and 3rd gear from worn clutches, Transmission overheating from failed oil cooler lines, Hard shifting or delayed engagement when cold
Fix: The THM 325-4L overdrive automatic is weak behind these engines. Failed oil coolers contaminate the transmission (replace both, 8-10 hours). Full rebuilds run 16-20 hours. Cooler line replacements are preventive maintenance at 12+ years old.
Estimated cost: $2,200-3,500 rebuild, $400-700 cooler replacement
Digital Fuel Injection (DFI) Computer and Sensor Failures
Occasional · medium severitySymptoms: Intermittent stalling and no-start conditions, Erratic idle speed hunting between 400-1200 RPM, Hard starting when hot, Throttle position sensor codes with surging acceleration
Fix: The early Cadillac DFI system uses fragile electronics and sensors that fail with age. ECM failures require a rebuilt unit (2-3 hours to install). Throttle position sensors and coolant temp sensors are common culprits (1-2 hours each). Diagnosing intermittent issues can add 2-4 hours of labor.
Estimated cost: $800-1,500 for ECM, $200-400 per sensor
Rear Main Seal and Oil Pan Gasket Leaks
Common · low severityTypical onset: 70,000-120,000 mi
Symptoms: Oil puddles under the rear of engine after sitting overnight, Oil coating on transmission bellhousing, Low oil level requiring frequent top-offs (1 quart per 500-1000 miles)
Fix: Rear main seal requires transmission removal (8-10 hours total). Oil pan gaskets leak from age and cork gasket deterioration (4-6 hours). Both are deferred maintenance until major engine work is needed, but can leave your driveway looking like Valdez.
Estimated cost: $600-1,000 rear main, $400-600 oil pan
Vacuum System Leaks Affecting HVAC and Accessories
Occasional · low severitySymptoms: HVAC defaults to defrost-only mode, Climate control blend doors won't change position, Cruise control inoperative or surging, Hissing sound from under dash
Fix: These cars use vacuum for numerous systems. Rubber vacuum lines become brittle after 40+ years. The vacuum reservoir canister can crack. Diagnosis takes 1-2 hours of checking lines and actuators, repairs are 2-4 hours depending on accessibility.
Estimated cost: $300-600
Only buy a 368-equipped example with documented recent transmission service—the diesel and V8-6-4 variants are money pits that will leave you walking, and parts availability gets worse every year.
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.