The 1991 Roadmaster with the 5.7L (350 TBI) is a solid body-on-frame sedan let down by GM's 4L60 (700-R4 derivative) transmission and fuel system quirks. Engine internals fail catastrophically when the Optispark distributor (added in '94) isn't the issue, but these earlier TBI motors suffer piston ring and bearing wear from oil consumption neglect.
4L60 Transmission Failure (Internal Clutch Pack & Overheating)
Common · high severityTypical onset: 90,000-150,000 mi
Symptoms: Delayed or harsh 1-2 shift, slipping on acceleration, Transmission fluid dark brown or burnt smell, Whining noise in overdrive, especially under load, Check Engine light with transmission codes (on OBD-I scanner)
Fix: Rebuild or replacement required. Internal 3-4 clutch packs wear from inadequate factory cooling. External auxiliary cooler should be added during rebuild (2 hours for cooler install). Total rebuild time 8-12 hours depending on removal complexity.
Estimated cost: $1,800-2,800
Piston Ring Wear & Oil Consumption (5.7L TBI)
Common · medium severityTypical onset: 120,000-180,000 mi
Symptoms: Blue smoke on startup or acceleration, burning 1+ quart per 500-800 miles, Carbon buildup on spark plugs, misfires on cold start, Low compression readings (under 120 psi) on multiple cylinders, Oil fouling of catalytic converter, rotten egg smell
Fix: Top-end rebuild minimum: heads off, hone cylinders, new rings, valve seals (18-24 hours). If cylinder taper exceeds .003 inch, needs full rebuild or short block. Many owners just feed it oil until rod knock starts.
Estimated cost: $2,200-4,500
Fuel Pump & Sender Unit Failure
Common · high severityTypical onset: 80,000-130,000 mi
Symptoms: No-start or stalling after sitting, especially in hot weather, Fuel gauge erratic or stuck on empty/full, Whining noise from rear when key on, then silence, Pressure drops below 9 psi at idle (TBI spec is 9-13 psi)
Fix: In-tank pump replacement requires dropping 25-gallon tank (1.5 hours). Sender unit often corrodes at wiring connector. Replace both together with new strainer sock. Plastic fuel lines at tank crack, add 0.5 hours if replacement needed.
Estimated cost: $450-750
Transmission Oil Cooler Line Corrosion & Leaks
Common · medium severityTypical onset: 70,000-120,000 mi
Symptoms: Transmission fluid dripping near radiator or along frame rail, Pink fluid spots on driveway, ATF smell after driving, Low fluid level causing delayed engagement or slipping, Rust holes visible on steel cooler lines at bends/brackets
Fix: Factory steel lines rust through at mounting points and bends. Replace with pre-bent lines (1.5-2 hours) or upgrade to stainless braided hoses. Flush cooler in radiator to check for contamination. Rust in cooler means transmission rebuild is coming soon.
Estimated cost: $280-500
Intake Manifold Gasket Leaks (Coolant & Vacuum)
Occasional · medium severityTypical onset: 100,000-160,000 mi
Symptoms: Coolant seepage at front or rear of intake, white crusty buildup, Rough idle, high idle, or stalling when warm, Coolant loss with no external leaks visible, sweet smell from vents, Misfires on bank with vacuum leak, P0300-series codes
Fix: Remove TBI unit and upper plenum, replace lower intake gaskets (Felpro 1200-series recommended, not OEM composite). 4-6 hours labor. Check EGR valve and clean ports while open. Coolant crossover tube o-rings fail simultaneously, replace together.
Estimated cost: $550-900
Rear Main Seal Oil Leak
Occasional · low severityTypical onset: 110,000-180,000 mi
Symptoms: Oil dripping from bellhousing bottom, coating transmission case, Oil spots on driveway after sitting overnight, No smoke, no oil on exhaust manifolds (rules out valve covers)
Fix: Two-piece rope seal design leaks as rope compresses. Requires transmission removal (5-7 hours total). Many techs live with it if drips are slow—loses maybe 1 quart per 3,000 miles. Not worth fixing unless transmission is already out for other work.
Estimated cost: $650-1,100
Hood Latch Cable Corrosion & Secondary Latch Failure
Occasional · low severitySymptoms: Hood won't release from inside, cable feels slack or broken, Secondary safety catch rusted, hood pops up while driving (rare but serious), Cable frayed at handle or latch mechanism in front clip
Fix: NHTSA recall addressed secondary latch, but cable itself wasn't recalled. Replace cable (1 hour), lubricate latch pivot points. If secondary catch is rusted solid, hood can open unexpectedly—check both systems before highway driving.
Estimated cost: $120-220
Buy one under 100k miles with service records showing frequent transmission fluid changes; budget $1,500-2,000 for deferred maintenance and expect to nurse oil consumption or rebuild the trans by 150k.
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.