1972 PONTIAC BONNEVILLE

Typical onset: 80,000-120,000 mi

Symptoms: Blue smoke on startup or acceleration, Fouled spark plugs, Oil level drops quart per 500-800 miles, Carbon buildup on intake valves

Fix: The low-compression 8.2:1 engines in '72 run soft rings that wear quickly under sustained highway use. Proper fix requires ring replacement (8-12 hours) or short block swap if cylinder taper exceeds .010". Ridge reaming and honing mandatory. Many shops go straight to reman short block to avoid comebacks.

Estimated cost: $1,800-3,200

Typical onset: any mileage—corrosion-driven

Symptoms: ATF puddle under radiator area, Transmission slipping after warmup, Pink milkshake in radiator or ATF in coolant, Sudden loss of forward gears

Fix: Steel cooler lines rust through at bends near radiator or frame brackets, especially in salt states. If ATF mixes with coolant through internal radiator leak, transmission is toast—requires flush, converter replacement, and often full rebuild. External line replacement alone is 1.5-2 hours; contamination scenario runs 12-18 hours total.

Estimated cost: $150-400 for lines alone; $2,200-3,800 with transmission rebuild

Typical onset: 100,000-150,000 mi

Symptoms: Deep knock at idle that worsens with RPM, Oil pressure drops below 10 psi hot idle, Metallic debris in oil filter, Vibration through drivetrain

Fix: The 455 especially suffers from main bearing failure due to marginal oiling in stock configuration and owner neglect of oil changes. Requires crankshaft removal, journaling/polishing (.010" or .020" undersize bearings), line boring if saddles are damaged. Total engine-out job: 16-22 hours. Many opt for reman long block instead of machine work gamble.

Estimated cost: $3,500-5,500

Typical onset: 60,000-100,000 mi

Symptoms: Clunk when shifting from Park to Drive, Excessive driveline vibration at 40-50 mph, Transmission tail visible sagging below crossmember, Harsh engagement into gear

Fix: Rubber mount deteriorates from heat and age; TH400 tailshaft drops and causes U-joint angles to go out of spec. Replacement is straightforward—support transmission, swap mount—but requires transmission jack or jackstands. 1-1.5 hours labor. Inspect U-joints and driveshaft balance while you're under there.

Estimated cost: $120-220

Symptoms: Fuel smell in garage after sitting, Black smoke at idle, Stumble or stall when coming to stop, Hard cold starts despite new choke

Fix: The Q-jet's needle-and-seat wear allows fuel to seep past, flooding the intake. Float level goes out of spec, and accelerator pump diaphragms crack. Full carb rebuild kit (3-4 hours including removal/bench work) usually solves it. Alternatively, Edelbrock/Holley swaps are popular but lose some low-end torque. Set float at 7/16" and check secondary air valve tension.

Estimated cost: $350-650

Typical onset: 70,000-110,000 mi

Symptoms: Power steering fluid puddle on driver-side engine bay, Whining noise that rises with RPM, Steering effort increases when fluid runs low, Burnt smell from fluid hitting exhaust manifolds

Fix: Saginaw pump's front seal dries out and weeps; harmonic balancer pulley wobble accelerates wear. Seal replacement is 1.5-2 hours if you pull pump (need pulley puller). Flush system with fresh Dexron and inspect pressure hose for cracks. Low-cost fix but messy—ATF gets everywhere.

Estimated cost: $180-320