The 2004 Buick Century with the 3.1L V6 is a comfortable, affordable mid-size sedan plagued primarily by known GM 3100/3400 engine weaknesses—namely intake manifold gasket failures and head gasket issues that can cascade into catastrophic internal damage if ignored. Transmission cooler line corrosion is also a repeat offender.
Symptoms: Coolant loss with no visible external leaks, White smoke from exhaust on cold start, Milky oil on dipstick or oil cap, Overheating or rough idle
Fix: Replace lower intake manifold gaskets (plastic OEM gaskets rot out), upper plenum gaskets, thermostat, and flush contaminated coolant. Use updated Fel-Pro or Felpro PermaDryPlus gaskets. 6-8 labor hours.
Estimated cost: $800-1,400
Head Gasket Failure / Coolant-in-Oil Contamination Leading to Bearing Damage
Occasional · high severity
Typical onset: 100,000-150,000 mi
Symptoms: Continued coolant loss after intake gasket replacement, Persistent milky oil, chocolate milk appearance, Knocking or ticking from lower end as bearings wash out, Loss of compression, misfires
Fix: If caught early, head gasket replacement runs 10-12 hours. If coolant contaminated oil and starved bearings, you're into a short block or full engine rebuild—new pistons, rings, bearings, machine work. Many owners opt for a salvage yard 3.1L or upgrade to 3100/3400 known-good engine. 18-24 hours for full rebuild.
Estimated cost: $1,200-2,000 (gaskets only) or $3,500-5,500 (rebuild/reman engine installed)
Transmission Oil Cooler Line Corrosion and Leaks
Common · medium severity
Typical onset: 80,000-130,000 mi
Symptoms: Transmission fluid dripping near radiator or under engine, Low transmission fluid level, slipping or delayed engagement, Rust spots or green coolant mixing with red ATF if internal radiator cooler fails
Fix: Replace steel cooler lines (they rust through at crimps and bends), often both feed and return. If radiator's internal ATF cooler failed, flush transmission and replace radiator to prevent total transmission failure. 2-3 hours for lines, 4-5 if radiator also needed.
Estimated cost: $300-600 (lines) or $700-1,100 (lines + radiator + trans flush)
Transmission Mount Collapse
Common · low severity
Typical onset: 70,000-110,000 mi
Symptoms: Clunk or thud when shifting from Park to Drive/Reverse, Excessive engine movement visible from engine bay on acceleration, Vibration at idle
Fix: Replace rear transmission mount (hydraulic mount fails, oil leaks out). Straightforward but requires supporting transmission. 1.5-2 hours.
Estimated cost: $180-320
Fuel Tank Pressure Relief Valve Issues (Recall-Related)
Occasional · medium severity
Symptoms: Check engine light with evap system codes (P0440, P0442), Fuel smell near tank, especially after filling, Difficulty fueling, pump clicks off repeatedly
Fix: NHTSA recall 04V258000 addressed pressure relief in filler neck assembly. If not done, replace fuel tank pressure sensor or vent valve solenoid. Also check for rusted filler neck. 1.5-2.5 hours depending on component.
Estimated cost: $250-500
Power Steering Pump Whine and Rack Leaks
Occasional · low severity
Typical onset: 90,000-140,000 mi
Symptoms: Whining noise on turns, worse when cold, Power steering fluid leak from rack boots or pump, Heavy steering effort
Fix: Replace power steering pump or rack seals. Rack replacement is 4-5 hours; pump is 2-3 hours. Flush system with fresh fluid.
Estimated cost: $350-600 (pump) or $600-1,000 (rack)
Owner tips
Flush Dexcool coolant every 3 years and switch to traditional green coolant or use Peak extended-life that's intake-gasket safe
Monitor oil condition religiously—any milky appearance means stop driving immediately to save the bottom end
Inspect transmission cooler lines annually for surface rust; replace proactively around 100k to avoid being stranded
Change transmission fluid every 50k miles; the 4T65E is sensitive to old fluid
Buy only if the intake gaskets have already been done with updated parts and the engine has no coolant-in-oil history—otherwise, budget $2k-4k for deferred engine work within a year.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.
Fitment notes: Side post terminals standard for GM vehicles of this era
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Every control module on the 1997-2005 Buick Century — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
⚠️ Optional on higher trim levels; requires memory position reprogramming by user
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
DORMAN IS RECALLING 979 STEERING KNUCKLES, DORMAN P/NOS. 697-902 AND 697-903, SOLD UNDER DORMAN'S "OE SOLUTIONS<SUP>TM</SUP>" BRAND NAME, AND NAPA P/NOS. 7-8502 AND 7-8503 WHICH WERE SOLD FOR REPLACEMENT USE ON THE VARIOUS VEHICLES LISTED ABOVE. A POTENTIAL MATERIAL OR DESIGN DEFECT COULD RESULT IN THE STEERING KNUCKLE BREAKING IN THE HUB AREA.
Consequence: A BROKEN STEERING KNUCKLE COULD RESULT IN LOSS OF STEERING CONTROL AND A POSSIBLE CRASH WITHOUT WARNING.
Remedy: DORMAN WILL NOTIFY OWNERS AND REPLACE THE DEFECTIVE STEERING KNUCKLES FREE OF CHARGE AND REIMBURSE THE REPAIR FACILITY OR OWNER FOR LABOR. THE RECALL BEGAN ON FEBRUARY 23, 2009. OWNERS MAY CONTACT DORMAN'S TOLL-FREE HOTLINE AT 1-800-523-2492 AND PRESS 5.
CERTAIN DELPHI FUEL PRESSURE REGULATORS, P/NOS. FP10020-11B1, FP10026-11B1, AND FP10027-11B1, SOLD AFTER JANUARY 9, 2007, AS AFTERMARKET EQUIPMENT FOR VARIOUS PASSENGER VEHICLES LISTED ABOVE. THE UNIVERSAL PRESSURE REGULATORS (UPR) WERE PRODUCED WITHOUT AN O'RING AND RETAINER.
Consequence: FUEL MAY LEAK, POSSIBLY RESULTING IN A FIRE.
Remedy: DELPHI WILL NOTIFY OWNERS AND REPLACE THE UPR FREE OF CHARGE. THE RECALL BEGAN ON APRIL 23, 2007. OWNERS CAN CONTACT DELPHI AT 877-411-8770.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2004 Buick Century 3.1L V6 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.