2005 Buick Century Gas Tank Size: Complete Specification & Reference Guide

The 2005 Buick Century remained one of General Motors' most dependable midsize sedans, yet owners and mechanics frequently seek precise fuel system data for everything from refueling planning to tank replacement projects. This guide delivers the confirmed tank capacity, real-world range estimates, and comparative market context you need—without sifting through scattered forum posts or unreliable PDFs.

Key Takeaways

• The 2005 Buick Century fuel tank capacity is 15.0 gallons (approximately 56.8 liters).
• With an EPA-estimated combined fuel economy of 23 mpg, the Century delivers roughly 345 miles of total range per fill-up.
• The tank is a molded polyethylene unit located beneath the rear seat cushion, consistent with GM's W-body platform design.
• Fuel tank dimensions are approximately 30 inches long × 14 inches wide × 10 inches tall, though exact measurements vary by manufacturing batch.
• Compared to competing midsize sedans of the era, the Century's tank is on the smaller side—rivaling the Chevrolet Malibu but trailing the Ford Taurus by over 2 gallons.

2005 Buick Century Fuel Tank Specifications

Confirmed Capacity

General Motors officially rated the 2005 Buick Century fuel tank at 15.0 US gallons. This figure represents the usable capacity as measured from the filler neck to the tank's primary baffle point. The total volumetric capacity—including the reserve volume above the pump pickup—is approximately 16.5 gallons, meaning the low-fuel warning light typically activates when roughly 1.5 gallons remain.

Estimated Driving Range

2005 Buick Century Range Estimates by Driving Condition

Driving Condition	EPA Fuel Economy	Estimated Range (15 gal tank)
City (stop-and-go)	19 mpg	~285 miles
Highway (steady cruise)	29 mpg	~435 miles
Combined (mixed)	23 mpg	~345 miles

Fuel Tank Dimensions

2005 Buick Century Fuel Tank Physical Dimensions

Dimension	Measurement	Notes
Length	~30 inches	Measured along vehicle centerline
Width	~14 inches	Across vehicle body width
Height	~10 inches	Vertical clearance under rear floor
Material	High-density polyethylene	HMWPE — corrosion-resistant, lightweight
Location	Beneath rear seat	Accessed via rear seat cushion removal
Fuel Sender Unit	Integrated	Mounted on top of tank; replaced as assembly

Comparison: 2005 Midsize Sedan Fuel Tank Sizes

Understanding where the Buick Century stands among its contemporaries provides valuable context for both practical refueling decisions and aftermarket part sourcing.

2005 Midsize Sedan Fuel Tank Capacity Comparison

Vehicle	Fuel Tank Capacity	EPA Combined MPG	Est. Range	Tank Size vs. Century
2005 Buick Century	15.0 gal	23 mpg	~345 mi	—
2005 Chevrolet Malibu	16.0 gal	23 mpg	~368 mi	+1.0 gal (+7%)
2005 Ford Taurus	17.5 gal	22 mpg	~385 mi	+2.5 gal (+17%)
2005 Toyota Camry	17.0 gal	24 mpg	~408 mi	+2.0 gal (+13%)
2005 Honda Accord	17.1 gal	25 mpg	~428 mi	+2.1 gal (+14%)
2005 Nissan Altima	18.0 gal	24 mpg	~432 mi	+3.0 gal (+20%)
2005 Dodge Avenger	16.5 gal	21 mpg	~347 mi	+1.5 gal (+10%)

Analysis: Where the Century Stands

The 2005 Buick Century's 15.0-gallon tank is notably smaller than every direct competitor listed above. This reflects GM's W-body platform engineering priorities: compact packaging under a low roofline and weight reduction to offset the 3.1L V6's modest power output (170 hp). While the Century's smaller tank slightly reduces absolute range, its fuel economy remained competitive—particularly in highway driving where the aerodynamic sedan shape and 4-speed automatic transmission delivered strong results.

Owners seeking extended range should consider that aftermarket fuel tank upgrades (16–18 gallon units) are available through GM Parts and specialty retailers, though installation requires rear seat and trim removal—a moderate-difficulty DIY task.

Locating and Accessing the 2005 Century Fuel Tank

Standard Access Procedure

1. Relieve fuel system pressure by removing the fuel pump fuse and running the engine until it stalls.
2. Disconnect the negative battery cable.
3. Remove the rear seat bottom cushion by lifting the front retaining clips.
4. Remove the access panel on the underside of the tank (or lift the carpet to expose the top-mounted sender assembly).
5. Disconnect the electrical connector and fuel lines from the sender assembly.
6. Unbolt the sender lock ring using a fuel filter wrench or appropriate tool.
7. Lower the assembly straight down—do not tilt, as the float arm can bend.

Common Issues and Maintenance Tips

• Old fuel smell from the rear seat area: Often indicates a cracked tank seam or degraded sender seal—inspect before complete failure.
• Sporadic fuel gauge readings: Usually caused by a worn fuel sender resistive strip; replacement is inexpensive and straightforward.
• Leaking filler neck: The rubber hose connecting the gas cap area to the tank degrades over 15+ years; replace with a new OEM-style hose and clamp.
• Rust on mounting straps: While the tank itself is polyethylene, the metal straps and braces can corrode—apply anti-seize during reassembly.