1991 HYUNDAI SONATA

Typical onset: 80,000-140,000 mi

Symptoms: Loud knocking or rod knock at idle, worse when cold, Loss of oil pressure, flickering oil light, Metallic rattling that increases with RPM, Metal shavings in oil during changes

Fix: Main and rod bearings fail prematurely due to marginal oiling and soft bearing material. Requires complete teardown, crank polishing or replacement, new bearings, and piston inspection. Short-block replacement often more cost-effective than full rebuild. 18-24 labor hours for proper engine-out rebuild.

Estimated cost: $2,800-5,500

Typical onset: 70,000-110,000 mi

Symptoms: Transmission fluid leaking near radiator area, Erratic shifting or slipping between gears, Whining noise during acceleration, Milky or discolored transmission fluid indicating coolant contamination

Fix: Steel cooler lines rust through where they connect to radiator; coolant mixes with ATF and destroys transmission internals. Requires line replacement, external cooler addition, full fluid flush, and often transmission rebuild or replacement if contamination occurred. 8-12 hours for transmission R&R plus rebuild time.

Estimated cost: $1,800-3,200

Typical onset: 90,000-130,000 mi

Symptoms: White smoke from exhaust on startup, Overheating with no external coolant leaks, Bubbles in coolant reservoir when running, Oil with milky appearance or coolant loss without visible leaks

Fix: V6 head gaskets fail between cylinders or into coolant jackets. Both heads must come off; always resurface heads, replace timing belt/water pump while apart. 14-18 labor hours. The 2.4L four-cylinder has this less often but same repair complexity.

Estimated cost: $2,200-3,800

Typical onset: 60,000-80,000 mi

Symptoms: Squealing from front of engine, Coolant leak from water pump weep hole, Engine won't start after belt breaks (interference engine), Visible belt cracking or glazing

Fix: Both engines are interference design; belt failure bends valves. Belt service interval was originally 60k but many fail earlier. Always replace water pump, tensioner, and idler pulleys together. If belt breaks, expect valve job or head work. 4-6 hours for preventive service, 12-16 if valves bent.

Estimated cost: $450-800 preventive / $2,000-3,500 after failure

Typical onset: 100,000-150,000 mi

Symptoms: Hard starting when hot, Rough idle and misfires, Loss of power under acceleration, Stalling at stops after highway driving

Fix: In-tank fuel pump sock clogs, fuel filter neglect common, and injectors develop varnish from poor fuel quality. Full fuel system cleaning with new filter, injector service, and sometimes pump replacement needed. 3-5 hours depending on severity.

Estimated cost: $400-900

Typical onset: 60,000-100,000 mi

Symptoms: Clunk when shifting from park to drive, Excessive engine movement visible from driver seat, Vibration through steering wheel at idle, Difficulty shifting smoothly

Fix: Hydraulic front mount deteriorates quickly, letting engine rock excessively and stressing halfshafts. Replace all three mounts as a set; front mount alone is 2 hours, all three is 3-4 hours.

Estimated cost: $350-650

Typical onset: 80,000-120,000 mi

Symptoms: Plastic radiator tank cracking at seams, Overheating in traffic or summer heat, Coolant puddles under car after sitting, Heater blows cold at idle

Fix: Plastic end-tank radiators crack, hoses become brittle, and thermostats stick. Entire cooling system refresh recommended: radiator, all hoses, thermostat, coolant flush. Prevents head gasket failure. 4-5 hours for complete overhaul.

Estimated cost: $500-850