The 2004 Mercedes-Benz CLK55 AMG is a high-performance grand tourer powered by a naturally aspirated 5.5-liter V8 engine. This engine, identified by code 5439cc 2, produces significant horsepower and torque, operating at higher temperatures and RPMs than standard passenger cars. To maintain peak performance and longevity, the lubrication system must meet rigorous European standards. Standard mineral oils simply cannot withstand the thermal and mechanical stress placed on this powerplant, making the use of 100% synthetic lubricants a necessity rather than an option.
Recommended AMSOIL Products
- AMSOIL 5W-40 FS 100% Synthetic European Motor Oil – Specifically formulated for the unique demands of European gasoline and diesel engines, featuring a precise blend of synthetic base oils.
- AMSOIL 0W-40 FS 100% Synthetic European Motor Oil – An excellent choice for extreme cold starting while maintaining robust protection at high operating temperatures.
- AMSOIL Oil Filter – Offers filtering efficiency of 99 percent at 20 microns, providing superior capacity for contaminants to protect the engine’s vital components.
- WIX Oil Filter – A premium alternative featuring advanced media that offers improvements over standard original equipment manufacturer branded filters.
- MANN-FILTERS Oil Filter – Utilizes premium media designed to meet the high standards required by this specific Mercedes-Benz engine.
- AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Withstands heavy towing and elevated temperatures, remaining fluid in sub-zero conditions.
- AMSOIL OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – A cost-effective synthetic option that protects against wear in the 5-speed automatic transmission.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – A 50/50 pre-mix formulation that protects all cooling system metals, gaskets, and hoses for up to 150,000 miles.
- AMSOIL Propylene Glycol Antifreeze and Engine Coolant – A concentrated formula that requires mixing with water, offering protection up to 150,000 miles or 5 years.
- AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid – Provides excellent ABS and traction-control responsiveness with a stable viscosity over a wide temperature range.
- AMSOIL 100% Synthetic Multi-Vehicle Power Steering Fluid – Reduces friction and helps seals remain soft to prevent leaks, ensuring quiet operation.
Engine Oil and Filtration
The heart of the 2004 CLK55 AMG is the 5.5-liter M113K engine. This powerhouse requires a lubricant that can handle the high shear forces and heat generated during spirited driving or highway cruising. The engine oil capacity is 9.0 quarts when performing a filter change. It is important to note that on models equipped with an oil cooler, additional oil may be required if the cooler is drained during the service. Always allow at least five minutes after refilling or turning the engine off before checking the oil level to ensure accuracy. The drain plug torque specification is 27 ft/lbs.
AMSOIL offers two distinct grades of European-formulated motor oil for this vehicle. The AMSOIL 5W-40 FS provides a balanced viscosity profile suitable for a wide range of temperatures. Alternatively, the AMSOIL 0W-40 FS offers superior cold-start protection, making it ideal for owners in colder climates who still require robust high-temperature performance. Both oils feature a precise blend of synthetic base oils and premium additives designed for the specific tolerances of European engines. These formulations ensure engine cleanliness and wear protection, extending the service life of the powertrain.
Filtration is equally critical. The recommended AMSOIL Oil Filter (Code EA15K39-EA) is engineered to provide filtering efficiency of 99 percent at 20 microns. It offers greater capacity for small, wear-causing contaminants than competing filters, helping to reduce engine wear and allowing the engine to run smoother for longer intervals. For those who prefer established brands, the WIX Oil Filter (Code 51226-EA) and MANN-FILTERS Oil Filter (Code HU7185X-EA) are also recommended, both utilizing premium media that offers improvements over standard OEM filters.
Transmission and Drivetrain Fluids
The CLK55 AMG is typically equipped with a 5-speed automatic transmission (722.6), a unit known for its smooth shifts but sensitive to fluid degradation. Maintaining the integrity of this fluid is crucial for preventing sludge buildup and ensuring the transmission lasts for the life of the vehicle. The total fill capacity for the transmission is 9.2 quarts.
AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid is designed to withstand the rigors of heavy towing, elevated temperatures, and challenging terrain. It remains fluid in sub-zero temperatures, providing reserve protection during heavy use. For those seeking a more budget-friendly synthetic option, the AMSOIL OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid is a robust choice that protects against wear without compromising performance. Both fluids are engineered to exceed original equipment manufacturer requirements, ensuring the transmission operates quietly and efficiently.
Regarding the differential and transfer case, the rear axle requires 3 pints of lubricant. While specific AMSOIL gear lubricants are often recommended for rear axles under heavy load, the vehicle’s manual should be consulted for the specific viscosity grade. The focus remains on using high-quality synthetic lubricants that resist thermal breakdown and oxidation, ensuring the differential gears are properly lubricated even under high torque conditions.
Brake, Steering, and Cooling Systems
Brake fluid is a hygroscopic fluid, meaning it absorbs moisture from the atmosphere over time. This can lower the boiling point and lead to brake fade or ABS failure. For the CLK55 AMG, AMSOIL recommends a DOT 4 plus fluid that meets MB Sheet 331.0 specifications. The AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid is an excellent choice, offering stable viscosity and excellent responsiveness for the vehicle’s braking system.
The power steering system also benefits from synthetic fluid. The AMSOIL 100% Synthetic Multi-Vehicle Power Steering Fluid is formulated to reduce friction, keep seals soft to prevent leaks, and resist heat for long fluid life. This ensures quiet operation and protects the steering pump and rack from wear.
Cooling system maintenance is vital for this high-output engine. The coolant capacity is 12.7 quarts. Owners can choose between a 50/50 pre-mix formulation, the AMSOIL Passenger Car & Light Truck Antifreeze & Coolant, or the concentrated AMSOIL Propylene Glycol Antifreeze and Engine Coolant which requires mixing with distilled water. Both options provide protection against corrosion and erosion for up to 150,000 miles or 5 years, protecting all cooling system metals, gaskets, and hoses.
Additional Care and Seasonal Maintenance
Beyond the essential fluids, maintaining the fuel system and preparing the vehicle for storage can significantly extend its life. For daily driving, the AMSOIL P.i. Performance Improver Gasoline Additive can help restore fuel injectors to 100% flow rate and improve fuel economy. For seasonal storage, products like the AMSOIL Gasoline Stabilizer keep fuel fresh for up to 12 months, while the AMSOIL Engine Fogging Oil protects internal engine components during long periods of inactivity.
Cleaning and protection products also play a role in maintaining the vehicle’s condition. The AMSOIL Heavy-Duty Degreaser effectively removes grease and grime from engine surfaces, while the AMSOIL Brake and Parts Cleaner leaves no residue on braking components. For exterior protection, the AMSOIL High-Foam Car Shampoo is hard on dirt but gentle on coatings, and the AMSOIL Exterior Ceramic Spray sheds water rapidly and protects against UV rays.
About the Vehicle
The 2004 Mercedes-Benz CLK55 AMG represents a pinnacle of early 21st-century grand touring. Part of the W209 generation of the CLK class, the CLK55 AMG was the high-performance variant developed by Mercedes-AMG. It was not merely a cosmetic upgrade; it featured the robust M113K 5.5-liter naturally aspirated V8 engine, which was a badge of engineering excellence for Mercedes-Benz at the time.
Owners of this vehicle often cite its driving character as the primary reason for their affection. Unlike the supercharged models that came later, the CLK55 AMG was beloved for the linear, throaty power delivery of its high-revving V8. The car offered a perfect balance between a luxury coupe and a sports car, providing high-speed stability and comfortable handling without sacrificing the smooth ride quality expected of a Mercedes-Benz. The design language of the W209, with its distinctive double-hump grille and sleek coupe silhouette, remains a classic automotive shape that ages gracefully.
Maintaining a CLK55 AMG requires an understanding that it is a precision instrument. While it is a reliable vehicle when properly cared for, its components are sensitive to degradation. Regular maintenance using high-quality fluids is essential to preserve the performance for which this model was famous. Whether it is a weekend cruiser or a daily driver, keeping the engine oil, transmission fluid, and cooling system in peak condition ensures that the CLK55 AMG continues to deliver the performance and reliability that owners value.
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