1988 CADILLAC SEVILLE

Typical onset: 60,000-100,000 mi

Symptoms: Coolant consumption with no visible leaks, White smoke from exhaust, Milky oil on dipstick, Overheating despite new thermostat and water pump, Loss of compression in multiple cylinders

Fix: The aluminum block suffers from porosity allowing coolant seepage into cylinders and crankcase. Head gaskets fail due to inadequate clamping force from the block design. Real fix requires engine replacement or complete rebuild with aftermarket head studs, block sealing, decking both heads and block. Figure 18-24 labor hours for R&R plus rebuild time. Most shops recommend used 4.5L or 4.9L swap instead.

Estimated cost: $3,500-6,500

Typical onset: 80,000-120,000 mi

Symptoms: Sudden coolant loss, External coolant weeping between cylinders 3-4 or 6-7, Misfire that moves between adjacent cylinders, Overheating that doesn't respond to repairs

Fix: The HT-4100 block cracks in the valley between cylinders from thermal stress and thin casting. Not repairable with sealants despite what bottles claim. Requires complete engine replacement. Short block alone won't save you — used complete engines are cheaper than machining. 20-26 hours R&R in FWD transverse configuration.

Estimated cost: $4,000-7,000

Symptoms: Stalling at stops after warmup, Surging idle between 400-1200 RPM, No-start when hot, Check Engine light with codes 21 or 34, Hesitation off idle

Fix: The TPS wears out its carbon traces and the ISC motor gear strips or sticks. Both live on the throttle body. Replace both together since you're there anyway. 1.5-2.5 hours labor. The Digital Fuel Injection system is parts-availability challenged — buy quality remans, not cheap rebuilds.

Estimated cost: $350-650

Typical onset: 70,000-110,000 mi

Symptoms: ATF dripping from radiator area, Pink fluid on ground after parking, Low transmission fluid without visible leaks underneath, Transmission slipping after short drives

Fix: Steel cooler lines rust through where they connect to the radiator and at frame contact points. Lines are NLA from GM — you'll fabricate custom lines or use universal transmission cooler line kits. Add external cooler while you're at it since these transaxles run hot. 2-3 hours labor plus fluid.

Estimated cost: $400-700

Typical onset: 50,000-90,000 mi

Symptoms: Blue smoke on startup, Consuming 1+ quart per 500-800 miles, Fouled spark plugs on cylinders 1, 4, 6, or 8, Loss of power under load, Positive crankcase pressure blowing out PCV

Fix: Soft piston rings and inadequate ring tension from factory. Cylinder walls score easily. If compression test shows under 120 PSI on any cylinder, you're doing rings minimum, likely full rebuild. Pulling heads reveals scored bores 80% of the time. 22-28 hours for proper rebuild, boring, honing, new pistons. Not worth it — engine swap time.

Estimated cost: $3,800-5,500

Symptoms: Fuel gauge reads empty when tank is full, Speedometer drops to zero intermittently, Temperature display blanks out, Entire display goes dark then returns, Segments missing from digital readouts

Fix: Cold solder joints on the cluster circuit board and failing vacuum fluorescent displays. Remove cluster (1.5 hours), send out for rebuild to specialist ($250-400) or DIY resolder if you have skills. Original GM parts are extinct. This is more annoyance than breakdown risk.

Estimated cost: $400-650