The 2003 Infiniti FX35 is a sophisticated crossover that combines the handling of a sports car with the utility of an SUV. Under the hood lies the legendary VQ35DE engine, a 3.5-liter V6 known for its smooth power delivery and high-revving capabilities. To keep this engine running at its peak for years to come, selecting the correct lubricants is not just a maintenance task—it is a crucial step in preserving the vehicle’s performance and longevity. Using high-quality synthetic fluids ensures that the engine operates smoothly across extreme temperature ranges, resists the formation of sludge, and minimizes wear on critical components like the VQ35DE’s variable valve timing system.
Recommended AMSOIL Products
- AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil – The ultimate choice for maximum engine protection, extending oil change intervals up to 25,000 miles and offering superior wear resistance for the VQ35DE engine.
- AMSOIL Extended-Life 5W-30 100% Synthetic Motor Oil – A robust option that provides extended protection for up to 20,000 miles or one year, featuring enhanced cleaning power to keep the engine running smoother.
- AMSOIL OE 5W-30 100% Synthetic Motor Oil – An excellent outperforms conventional oils, designed to fight sludge and deposits while maintaining compatibility with original equipment manufacturer standards.
- AMSOIL 5W-30 100% Synthetic High-Mileage Motor Oil – Specifically formulated for vehicles with over 75,000 miles, this oil features boosted detergents and reduced viscosity loss to help older engines last longer.
- AMSOIL Oil Filter – Provides 99% filtering efficiency at 20 microns, allowing lower restriction and greater capacity to remove wear-causing contaminants from the engine oil.
- WIX Oil Filter – A premium aftermarket option with media that offers improvements over original equipment manufacturer-branded filters for reliable engine protection.
- WIX Air Filter – Premium filtration media that helps improve engine airflow and performance while protecting internal components from dust and debris.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – An ethylene glycol formulation that protects cooling system metals, gaskets, and hoses for up to 150,000 miles or five years.
- AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Designed to withstand heavy towing and elevated temperatures while providing reserve protection during demanding driving conditions.
- AMSOIL OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Offers reliable protection against wear and excellent cold-weather performance for the RE5R05A transmission.
- AMSOIL SEVERE GEAR 80W-90 100% Synthetic Gear Lube – Advanced protection against wear for front and rear differentials, containing friction modifiers ideal for limited-slip applications.
- AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid – Delivers excellent responsiveness for ABS and traction control systems with stable viscosity across 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 and high-temperature stability.
- AMSOIL P.i. Performance Improver Gasoline Additive – Restores up to 14% horsepower and cleans fuel injectors, helping to improve fuel economy and prevent pre-ignition knock.
When it comes to the VQ35DE engine found in the 2003 Infiniti FX35, the 5W-30 viscosity grade is the preferred specification for all temperature ranges. The engine requires a total oil capacity of 5.0 quarts, including the filter replacement. Ensuring the oil level is correct after refill is critical to maintaining proper lubrication and pressure within the complex valve train and bearing systems of this high-performance engine. The torque specification for the oil drain plug is 25 ft/lbs, so using a quality filter wrench and torque wrench during maintenance is recommended to prevent stripping the threads or leaking.
The cooling system of the FX35 is substantial, requiring 9.1 quarts of coolant. Maintaining the integrity of the cooling system is vital for the VQ35DE, which runs relatively warm during spirited driving or towing. AMSOIL antifreeze and coolant formulations are engineered to exceed OEM requirements, protecting against corrosion, cavitation, and freezing. For those who prefer a concentrated solution that can be mixed with distilled water for precise freeze protection, the propylene glycol-based option offers extended service life and broad compatibility with various metal types within the cooling system.
The transmission in the 2003 Infiniti FX35 is a five-speed automatic unit known as the RE5R05A. This transmission has a total fill capacity of 10.9 quarts. Automatic transmission fluid is a lifeblood component for this gearbox, as it handles the power of the V6 engine and transfers it to the all-wheel-drive system. Using a synthetic transmission fluid ensures that the fluid remains fluid in sub-zero temperatures and maintains its viscosity under the heat generated during heavy towing or mountain driving. The synthetic formulation resists thermal breakdown and oxidation, which helps prevent the sludge and varnish buildup that can lead to harsh shifting or premature transmission wear.
For the drivetrain components, the FX35 utilizes differentials that benefit from high-performance gear lubricants. The front differential requires 1.4 pints of lubricant, while the rear differential holds 3 pints. These areas often operate under high pressure and temperature, making the use of an extreme pressure synthetic gear lube highly beneficial. AMSOIL SEVERE GEAR products are formulated to control thermal runaway and protect against rust and corrosion. The presence of friction modifiers in these gear lubes is particularly useful for limited-slip differentials, ensuring smooth power delivery to all four wheels without the shudder or chatter associated with standard gear oils.
Brake and power steering systems also play a significant role in the overall safety and driving dynamics of the Infiniti FX35. Synthetic brake fluid offers a higher boiling point than conventional DOT 3 fluids, which reduces the risk of brake fade during repeated hard stops. For the power steering system, a synthetic multi-vehicle fluid helps prevent seal leaks and reduces friction, contributing to quieter and smoother steering response. Regular maintenance of these fluids can extend the life of seals and hoses, preventing costly repairs and ensuring the vehicle remains safe to drive in all conditions.
About the Vehicle
The 2003 Infiniti FX35 represents a pivotal moment in automotive history, as it was the year the FX line was born. Originally launched as the “Crossover Sport” concept, the FX35 quickly became a pioneer in a class that was non-existent at the time: the luxury performance crossover. It took the sporty, agile character of the Infiniti G35 sedan and lifted it onto a platform shared with the Nissan Xterra, creating a vehicle that could handle corners with precision while still offering the utility and all-wheel-drive capability needed for varied weather conditions. The FX35 is built on a rear-wheel-drive platform that has been modified to include a sophisticated all-wheel-drive system, a layout that is increasingly popular among drivers who value both sportiness and versatility.
At the heart of this capable machine is the VQ35DE engine, a 3.5-liter DOHC V6 that produces around 260 horsepower. This engine is renowned for its smooth power band, high-revving nature, and reliability. The VQ series, manufactured by Nissan, has won numerous awards and is widely regarded as one of the finest engine families ever produced. In the FX35, this engine provides ample power for passing maneuvers and highway merging, while the chassis tuning ensures that the vehicle remains planted on the road. The suspension is a double-wishbone setup at both the front and rear, a configuration typically found on high-performance sports cars, which allows for excellent handling dynamics that set the FX35 apart from competitors that prioritize comfort over agility.
Despite its reputation for reliability, the FX35 does share some common issues with its sibling, the G35, particularly related to the VQ35DE engine family. One of the most frequently reported problems is the “rattle” of the upper timing chain guides. Over time, the plastic guides can wear or become brittle, leading to a noisy rattle on cold starts or during deceleration. This issue can be exacerbated by the use of lower-quality conventional oils that do not provide sufficient film strength. Using a high-performance synthetic oil like the Signature Series can help mitigate this by providing better lubrication to the timing chain tensioners and guides, potentially extending their lifespan.
Another common concern for owners of this vehicle is the tendency for the engine to consume oil as it ages. The variable valve timing (VVT) system, which is crucial for the engine’s performance, can be sensitive to oil pressure and cleanliness. As the vehicle accumulates mileage, the piston rings may not seal as tightly, leading to increased consumption. The AMSOIL High-Mileage Motor Oil is specifically designed to address this issue with enhanced additives that reduce oil consumption and help seal the gaps in the piston rings, allowing the engine to run cleaner and more efficiently. Additionally, the variable valve timing actuators can sometimes suffer from sludge buildup if oil changes are not performed frequently enough. A premium synthetic oil with superior cleaning power can help dissolve these deposits and keep the VVT system operating smoothly.
Finally, owners often report issues with the transmission shifting roughly, particularly in the lower gears, or experiencing shudder during acceleration. This can sometimes be traced back to the degradation of the transmission fluid over time. The fluid can break down under heat, leading to a loss of friction modifiers and a change in viscosity. Switching to a high-quality synthetic transmission fluid can restore proper shift feel, reduce shudder, and protect the clutch plates from premature wear. By addressing these specific maintenance needs with the recommended fluids, FX35 owners can ensure their vehicle continues to deliver the spirited driving experience that made it a favorite among enthusiasts.