1991 CADILLAC DEVILLE

Typical onset: 80,000-130,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant loss with no visible leaks, Overheating episodes, Milky oil on dipstick or oil cap, Sweet smell from exhaust

Fix: Both head gaskets should be replaced simultaneously even if only one side shows failure. Requires head removal, resurfacing, and updated gaskets. Budget 12-16 hours labor. Critical to address cooling system issues first or it will fail again. If coolant contaminated the oil and owner kept driving, expect bearing damage requiring full engine rebuild.

Estimated cost: $1,800-3,200

Typical onset: 70,000-120,000 mi

Symptoms: Pink or strawberry milkshake appearance in coolant reservoir, Transmission slipping or delayed engagement, Coolant level drops, Transmission fluid looks watery or discolored, Overheating of transmission

Fix: The cooler lines running through the radiator fail internally, allowing coolant and ATF to mix. Requires radiator replacement, complete transmission fluid flush (often multiple flushes), new cooler lines, and possibly transmission rebuild if contamination sat for any length of time. 8-12 hours labor if trans survives, 20+ if rebuild needed.

Estimated cost: $1,200-2,500 (cooler/lines/flush), $3,500-5,500 (with trans rebuild)

Symptoms: Speedometer, fuel gauge, or temp gauge reads incorrectly or not at all, Intermittent gauge cluster blackouts, Climate control stuck in one mode, Warning lights randomly illuminating, Door locks cycling on their own

Fix: The digital instrument cluster has cold solder joints on circuit boards and capacitor failures. BCM can also fail causing bizarre electrical gremlins. Cluster can sometimes be repaired by specialist (mail-in service), otherwise replacement with used unit. BCM replacement requires reprogramming. 2-4 hours labor for diagnosis and R&R.

Estimated cost: $400-1,200

Typical onset: 60,000-100,000 mi

Symptoms: Coolant seeping from rear of engine near firewall, Rapid coolant loss, Steam from under hood, Overheating after highway driving

Fix: The metal coolant crossover pipes at the back of the engine corrode and develop pinhole leaks or gasket failures. Requires removing upper intake plenum and accessories for access. Plastic elbow connectors also crack. Replace all coolant hoses in the area while you're in there. 4-6 hours labor.

Estimated cost: $600-1,100

Typical onset: 80,000-150,000 mi

Symptoms: Harsh clunk when shifting from Park to Drive or Reverse, Excessive engine/trans movement visible when accelerating, Vibration at idle in gear, Driveline shudder during acceleration

Fix: The rubber transmission mount and upper torque strut deteriorate, allowing excessive drivetrain movement. The strut in particular is a known weak point. Replace both mounts and inspect torque strut bushings. 2-3 hours labor.

Estimated cost: $350-600

Symptoms: No-start condition after rain or car wash, Rough idle and misfires in humid weather, Stalling when driving through puddles, Intermittent starting issues

Fix: While less common on the '91 4.9L than later LT1 engines, these distributors can still fail from moisture intrusion. Mounted low on front of engine behind water pump. Requires water pump removal for access. Install vented Optispark cap for preventive measure. 5-7 hours labor.

Estimated cost: $800-1,400

Typical onset: 90,000-140,000 mi

Symptoms: No-start with no fuel pressure, Stalling when fuel level drops below half tank, Fuel gauge reading erratically or stuck, Engine stumbling under acceleration

Fix: Factory fuel pumps eventually fail, and the in-tank sending unit develops corroded contacts causing erratic gauge readings. Replace pump and sending unit together. Requires dropping fuel tank. 3-4 hours labor.

Estimated cost: $500-850