The 1978 Buick Century is a solid mid-size A-body that suffers primarily from GM's infamous 350 diesel engine failures and transmission mount/cooler issues common to all TH200/TH350 applications of this era. The gas engines are generally reliable workhorses if maintained.
350 Diesel Engine Catastrophic Failure
Common · high severityTypical onset: 60,000-90,000 mi
Symptoms: White smoke from exhaust, Coolant contamination in oil (milky dipstick), Loss of compression, Sudden no-start with seized engine, Metal shavings in oil
Fix: GM's 5.7L diesel used gasoline-engine-based block with inadequate head bolts and weak main caps. Head gasket failures cascade into block cracking. Repair requires complete engine replacement or rebuild with extensive machine work. Expect 25-35 hours for R&R plus machine shop time and parts.
Estimated cost: $4,500-8,000
Transmission Mount Failure
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: Clunking on acceleration/deceleration, Excessive driveline vibration, Visible sag of transmission tailshaft, Difficulty shifting into gear
Fix: Rubber transmission mounts deteriorate and separate, allowing excessive drivetrain movement. Common across all A-body cars with TH200/TH350. Simple replacement takes 1.5-2 hours on a lift with exhaust work sometimes needed for access.
Estimated cost: $150-300
Transmission Oil Cooler Line Corrosion and Leaks
Common · medium severityTypical onset: 80,000-150,000 mi
Symptoms: Transmission fluid spots under car, Low fluid level on dipstick, Rust staining at radiator connections, Slipping or delayed engagement when fluid gets low
Fix: Steel cooler lines rust through at bends and radiator connections, especially in salt states. Replacement lines are cheap but routing through frame and crossmember takes 2-3 hours. Must refill and check for proper shifting afterward.
Estimated cost: $200-400
231 V6 Crankshaft and Main Bearing Wear
Occasional · high severityTypical onset: 120,000-180,000 mi
Symptoms: Deep knocking noise from bottom end, Low oil pressure at idle, Metal particles in oil filter, Gradual power loss
Fix: The Buick 231 V6 (3.8L) can develop main bearing wear, especially if oil changes were neglected. Requires complete teardown, crank grinding/replacement, and new bearings. Short block replacement often more cost-effective than full rebuild. Engine R&R plus machine work: 18-25 hours total.
Estimated cost: $2,800-4,500
Carburetor Rochester 2-Barrel Varnish and Wear
Common · low severitySymptoms: Hard starting when cold, Rough idle and stalling, Black smoke or hesitation on acceleration, Poor fuel economy
Fix: Ethanol fuel gums up the Rochester 2GC/2GE carburetors on gas engines after sitting or with irregular use. Usually needs complete rebuild with new jets, gaskets, and accelerator pump. DIY-friendly but finicky to tune. Professional rebuild: 2-3 hours.
Estimated cost: $250-450
Body Mount and Frame Rot (Rust Belt)
Occasional · high severitySymptoms: Doors misalign or don't close properly, Visible rust through at rocker panels, Body sags or leans, Floor pan holes visible from underneath
Fix: A-bodies in salt states rot at body mounts, frame rails behind front wheels, and floor pans. Body mount replacement requires lifting body off frame (12-16 hours). Frame section welding is specialized work. Inspect before purchase—uneconomical to repair on low-value cars.
Estimated cost: $1,500-3,500
Buy one with a gas engine and solid frame—avoid the diesel like the plague; these are cheap, simple cruisers that reward basic maintenance.
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.