1979 CADILLAC SEVILLE

Typical onset: 40,000-80,000 mi

Symptoms: excessive white or blue smoke, coolant loss with no visible leaks, hard starting when warm, loss of power under load, knocking or rattling from lower end

Fix: Head gasket failure from inadequate head bolt torque is the signature issue, often leading to cracked blocks and spun bearings. Most require complete engine replacement or rebuild including block work, updated head studs, and hardened valve seats. Engine-out rebuild runs 35-45 hours labor; many owners swap to gasoline 350 instead (25-30 hours including adapter work).

Estimated cost: $4,500-8,500

Typical onset: 60,000-100,000 mi

Symptoms: slipping on 1-2 or 2-3 shift, no reverse or intermittent reverse, delayed engagement, whining noise in gear, burnt fluid smell

Fix: The lightweight THM 200 behind the diesel was marginal from the factory. Intermediate band failures, weak direct clutches, and governor issues are typical. Full rebuild with updated parts required: 12-16 hours removal, rebuild, reinstall. Some shops won't touch them and recommend THM 350 swap instead (adds 4-6 hours).

Estimated cost: $2,200-3,800

Symptoms: rough idle or stalling, fuel in coolant or coolant in fuel, injector knock, poor fuel economy, fuel leaks at injection pump

Fix: Water intrusion through poorly-sealed fuel cap and internal coolant leaks contaminate the fuel system. Requires replacement of all filters, injection pump rebuild or replacement (8-12 hours), and often all eight injectors. Fuel tank cleaning adds another 4 hours. Preventive filter changes every 3,000 miles help but don't eliminate the issue.

Estimated cost: $1,800-4,200

Symptoms: AC blows hot or cold only, blower stuck on high or won't run, erratic temperature control, display shows wrong temperature, clicking from under dash

Fix: The early digital climate control uses a fragile programmer unit with vacuum servos and circuit boards that fail. New units haven't been available for years. Requires used replacement (2-3 hours dash disassembly) or conversion to manual controls (6-8 hours custom work). Most techs hunt for good used programmers.

Estimated cost: $600-1,200

Typical onset: any age in salt states

Symptoms: clunking over bumps, doors misalign suddenly, cracks in door jambs or rear quarter panel, visible rust at rocker panels, steering feels loose or wandering

Fix: The separate body-on-frame construction hides serious rust in the frame rails and body mounts, especially behind rear wheels and front subframe. Body mount replacement runs 8-12 hours; frame section repair adds 15-25 hours if welding is needed. Many cars are totaled by this rather than repaired.

Estimated cost: $1,200-4,500

Typical onset: all ages

Symptoms: headlight doors won't open or close, cruise control inoperative, HVAC doors stuck, hissing under dash, rough idle on gasoline engine

Fix: Dozens of vacuum lines for accessories and emissions become brittle and crack. Methodical replacement of all under-hood and under-dash lines required: 4-6 hours to do properly. Vacuum reservoir and check valves often need replacement too. Parts are cheap but labor is tedious.

Estimated cost: $450-850