The 1978 Buick Regal is a solid G-body platform with good bones, but the TH200/TH350 automatics are the weak link, and the 350 diesel should be avoided entirely. Most survivors with the 231 V6 or gas 350 V8 are dealing with transmission issues and engine wear from deferred maintenance in their third or fourth ownership cycle.
TH200 Transmission Failure (V6 models)
Common · high severityTypical onset: 60,000-90,000 mi
Symptoms: Slipping between 1st and 2nd gear under moderate throttle, No 3rd gear or delayed engagement, Burnt transmission fluid smell, Harsh downshifts or flare-ups
Fix: The TH200 behind the 231 V6 was underbuilt from the factory and cannot handle even mild abuse. Rebuild requires 8-12 hours with upgraded clutches and bands. Many shops recommend swapping to a TH350 instead (adds 4-6 hours for crossmember/linkage work). Expect core, rebuild kit, and fluids.
Estimated cost: $1,400-2,200
350 Oldsmobile Diesel Engine Catastrophic Failure
Common · high severityTypical onset: 40,000-80,000 mi
Symptoms: White smoke on startup, Coolant in oil (milkshake dipstick), Loss of power and hard starting, Head gasket failure leading to cracked block
Fix: The 5.7L diesel has inadequate head bolts and poor head gasket design. Once it blows, you're looking at heads, gaskets, bolts, injectors, and often a cracked block. Most owners swap to a gas 350 Chevy small-block (20-30 hours with mounts, exhaust, wiring). Rebuilding the diesel is throwing good money after bad.
Estimated cost: $4,500-7,500
Upper Engine Wear on 231 V6 (Oil Starvation)
Occasional · medium severityTypical onset: 100,000-150,000 mi
Symptoms: Lifter tick on cold starts that doesn't go away, Low oil pressure at idle when hot, Blue smoke on deceleration, Rattling from valvetrain
Fix: The Buick 231 (3.8L) had marginal oiling to the rocker arms, especially if oil changes were skipped. Valve job with lifter replacement is 10-14 hours. If main bearings are also worn (common), you're looking at a full rebuild or low-mile junkyard engine swap. Cores are still available but getting scarce.
Estimated cost: $1,800-3,200
Transmission Mount and Crossmember Deterioration
Common · low severityTypical onset: any mileage (age-related)
Symptoms: Clunk when shifting from park to drive, Vibration at highway speeds, Visible sagging of transmission tailshaft, Exhaust rattling against floor pan
Fix: Rubber transmission mount and the stamped steel crossmember both rot out from road salt and age. The mount is 1-2 hours, but if the crossmember is Swiss cheese (common in rust-belt cars), you're welding or replacing it (adds 3-4 hours). Check carefully on lift before purchase.
Estimated cost: $150-600
Carburetor Issues on Gas Engines (Rochester 2-bbl and 4-bbl)
Occasional · medium severitySymptoms: Flooding and fuel smell in garage, Stumble off idle or bog on acceleration, High idle that won't come down, Hard starting when warm
Fix: The Rochester carbs are rebuildable but suffer from warped throttle shafts, worn needle-and-seat assemblies, and vacuum leaks. A proper rebuild with new jets, gaskets, and accelerator pump takes 3-5 hours. Ethanol fuel accelerates deterioration. Many owners swap to a basic Edelbrock or Holley for reliability (2-3 hours).
Estimated cost: $350-750
Rear Main Seal Leak (All Engines)
Occasional · low severityTypical onset: 80,000-120,000 mi
Symptoms: Oil drips from bell housing area, Oil spots under car after sitting overnight, Clutch contamination if manual (rare), Visible seepage around flex plate
Fix: The two-piece rear main seal loves to weep once the rope-style packing hardens. Transmission must come out (6-8 hours labor). Often combined with transmission rebuild or clutch work to save on duplicate labor. Not an emergency, but it will leave marks on your driveway.
Estimated cost: $450-850
Buy a 305 or gas 350 V8 car if you can find one; skip the diesel entirely and budget $1,500-2,000 for transmission work on any V6 car.
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.