1987 CADILLAC ELDORADO

Typical onset: 60,000-100,000 mi

Symptoms: excessive oil consumption (1 quart per 500-1000 miles), knocking or tapping from lower engine, coolant mixing with oil (milky dipstick), overheating despite new radiator/thermostat, loss of compression in one or more cylinders

Fix: The HT-4100's thin-wall aluminum block develops porosity and cracks, while inadequate oiling starves rod and main bearings. Most mechanics recommend complete engine replacement rather than rebuild due to block integrity issues. Expect 18-25 hours labor for long block swap including cooling system refresh and gaskets. Some owners opt for non-HT engine swaps (Olds 307, Chevy 350) which adds fabrication time but provides reliability.

Estimated cost: $3,500-6,500

Typical onset: 80,000-120,000 mi

Symptoms: pink or strawberry milkshake appearance in radiator, transmission slipping or delayed engagement, transmission fluid level mysteriously low, overheating transmission, coolant level dropping without external leaks

Fix: The internal transmission cooler inside the radiator fails, allowing coolant and ATF to mix - death sentence for the TH-425 transmission. Requires radiator replacement or external cooler bypass, complete transmission fluid flush (often multiple flushes), and frequently full transmission rebuild if contamination went unnoticed. 8-12 hours for cooler fix plus flush; add 16-20 hours if trans needs rebuild.

Estimated cost: $800-1,200 (cooler/flush only), $2,500-3,800 (with transmission rebuild)

Typical onset: 90,000-140,000 mi

Symptoms: harsh 1-2 or 2-3 shifts, slipping under acceleration, no reverse or intermittent reverse, whining noise in gear, transmission fluid burnt smell or dark color

Fix: The TH-425 (front-wheel-drive variant of TH-400) suffers from worn clutch packs, failing governor, and valve body issues. Governor failure is particularly common and causes erratic shifting. Full rebuild includes clutches, bands, seals, and typically governor and valve body refresh. 16-22 hours labor for R&R and rebuild. Some hard parts are getting scarce.

Estimated cost: $2,200-3,500

Typical onset: any mileage - age-related

Symptoms: high idle (1200-1500 RPM), stalling when coming to stop, surging idle, poor fuel economy, transmission shifting harshly or at wrong points, check engine light with codes 21 or 34

Fix: The TPS and ISC motor are early electronic fuel injection weak points that fail from heat and age. TPS failure causes drivability issues and incorrect transmission shift points. ISC motor carbon buildup or motor failure causes idle problems. TPS replacement is 1 hour, ISC cleaning/replacement is 1.5-2 hours. Often both need attention simultaneously on 35+ year old cars.

Estimated cost: $250-500

Symptoms: segments missing from digital displays, entire speedometer or fuel gauge blank, intermittent display when hitting bumps, dim or flickering displays, complete instrument cluster blackout

Fix: The vacuum fluorescent displays and circuit boards suffer from cold solder joints and component failure. Repair requires removing cluster (2 hours), then either sending to specialist for repair ($200-400) or sourcing used cluster. No modern replacement available - these are repair-only items. Speedometer accuracy affects transmission shift points on these cars.

Estimated cost: $350-650

Typical onset: 70,000-110,000 mi

Symptoms: clunking when shifting into drive or reverse, excessive vibration at idle, steering wheel shakes, visible engine movement when revving, driveline shudder under acceleration

Fix: The front-wheel-drive transverse V8 setup puts tremendous stress on engine and transmission mounts. Rubber deteriorates and hydraulic mounts leak. Front cradle mounts require partial subframe lowering. Plan 4-6 hours to replace engine mounts, transmission mount, and front cradle mounts as a set - doing one at a time accelerates wear on others.

Estimated cost: $600-950