The 2018 Subaru Legacy equipped with the powerful 3.6L six-cylinder engine (Engine Code EZ36D 6) requires precision lubrication to maintain its performance and longevity. As a naturally aspirated flat-six engine, the Legacy relies on high-quality synthetic fluids to manage heat and ensure smooth operation under varying driving conditions. Using the correct oil viscosity and compatible fluids for the transmission, cooling system, and differentials is essential for preventing wear and maximizing the vehicle’s service life. Proper maintenance not only protects critical components but also supports the efficient operation of the vehicle’s all-wheel-drive system, a hallmark of Subaru engineering.
Recommended AMSOIL Products
- AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil – Offers the highest level of protection with up to 25,000 miles of service, providing superior resistance to wear and horsepower loss.
- AMSOIL Extended-Life 5W-30 100% Synthetic Motor Oil – Delivers 20,000 miles of protection with enhanced cleaning power to keep the engine running smoothly over time.
- AMSOIL OE 5W-30 100% Synthetic Motor Oil – A cost-effective option that outperforms conventional oils and meets the required viscosity standards for normal service intervals.
- AMSOIL 5W-30 100% Synthetic High-Mileage Motor Oil – Specifically formulated for vehicles with over 75,000 miles to reduce sludge and combat oil consumption.
- AMSOIL Oil Filter – Engineered for maximum filtration efficiency and reduced restriction to ensure clean oil flows to all engine components.
- WIX Oil Filter – A premium alternative filter option that offers high-quality media for reliable engine protection.
- WIX Air Filter – Ensures clean air intake for optimal combustion and engine efficiency.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – Provides up to 150,000 miles of corrosion protection and temperature regulation in a pre-mix formula.
- AMSOIL Propylene Glycol Antifreeze and Engine Coolant – A concentrated, safer alternative that offers extended service intervals and excellent corrosion protection.
- AMSOIL 100% Synthetic CVT Fluid – Designed for the Subaru’s transmission to provide exceptional metal-to-metal frictional properties and durability.
- AMSOIL SEVERE GEAR® 80W-90 100% Synthetic Gear Lube – Ideal for GL-5 differential applications, offering advanced wear protection and thermal control.
- AMSOIL SEVERE GEAR® 75W-90 100% Synthetic Gear Lube – Suitable for temperatures down to -20°F with excellent shear stability and friction modifier content.
- AMSOIL SEVERE GEAR® 75W-110 100% Synthetic Gear Lube – A thicker viscosity option for limited-slip differentials requiring specific performance characteristics.
- AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid – Delivers superior boiling points and stable viscosity for responsive ABS and traction control performance.
Engine Oil and Maintenance Specifications
Selecting the right motor oil is critical for the 3.6L EZ36D 6 engine found in the 2018 Legacy. This engine requires a SAE 5W-30 viscosity for all temperature ranges. When performing a service, the system holds 6.9 quarts of oil when the filter is replaced. After refilling, it is essential to check the oil level to ensure proper coverage. The oil drain plug should be torqued to 33 ft/lbs, and a new washer must be installed on the drain bolt every time to prevent leaks. For vehicles with significant mileage, high-mileage formulations are available to address specific wear concerns.
AMSOIL Signature Series stands out as the premier choice for owners seeking the longest possible intervals, up to 25,000 miles or one year. This fluid offers 75% more engine protection against horsepower loss and wear compared to industry standards. For those prioritizing cleaning power and slightly shorter intervals, the Extended-Life 5W-30 provides up to 20,000 miles of protection while helping to keep the engine running smoother for longer. If budget is a primary factor without sacrificing synthetic benefits, the OE 5W-30 is a robust choice that fights sludge and deposits effectively. Additionally, for engines exceeding 75,000 miles, the High-Mileage 5W-30 features a boosted detergent package and enhanced anti-wear additives to reduce sludge and oil consumption.
Filtration is just as important as the oil itself. The AMSOIL Oil Filter (EA15K20-EA) provides filtering efficiency of 99 percent at 20 microns. It allows for lower restriction, ensuring that critical engine parts remain lubricated even under high-pressure conditions. The filter also holds a greater capacity for small, wear-causing contaminants than competing filters, contributing to extended service life. A WIX Oil Filter (51334-EA) serves as an excellent alternative, offering premium media that improves upon original equipment manufacturer-branded filters.
Transmission and Drivetrain Fluids
The 2018 Subaru Legacy utilizes a specific automatic transmission (TR690) that requires careful fluid maintenance. While the total fill capacity is 13.4 quarts, routine top-offs should follow manufacturer guidelines to ensure proper operation. The transmission relies on VTF22 fluid specifications. AMSOIL 100% Synthetic CVT Fluid (CVTQT-EA) is engineered to provide exceptional metal-to-metal frictional properties, ensuring smooth shifting and protection against wear even in severe driving conditions.
The rear differential of the Legacy is a crucial component of its all-wheel-drive system. Depending on the specific requirements and temperature ranges, either 80W-90 or 75W-90 synthetic gear lube is recommended. The capacity for the rear differential is 1.7 pints. For GL-5 applications requiring 80W-90, AMSOIL SEVERE GEAR 80W-90 (AGLPK-EA) offers advanced protection against wear, controls thermal runaway, and protects against rust and corrosion. It contains friction modifiers suitable for limited-slip applications. For extreme cold weather performance down to -20°F, AMSOIL SEVERE GEAR 75W-90 (SVGPK-EA) provides superior low-temperature flow and shear stability. If the differential requires a thicker fluid for specific operating conditions, AMSOIL SEVERE GEAR 75W-110 (SVTPK-EA) is available to handle the load while protecting seals and reducing operating temperatures.
Cooling, Braking, and Seasonal Care
Proper thermal management is vital for the 3.6L engine. The cooling system capacity is 7.4 quarts. AMSOIL Passenger Car & Light Truck Antifreeze & Coolant (ANTPC1G-EA) is a pre-mixed, 50/50 ethylene glycol formulation that exceeds OEM requirements. It is free from phosphates, nitrates, nitrites, silicates, borates, and amines, making it compatible with all cooling system metals, gaskets, and hoses. For those who prefer a concentrated formula, AMSOIL Propylene Glycol Antifreeze and Engine Coolant (ANT1G-EA) offers a safer, eco-friendly alternative that can last up to 150,000 miles or 5 years. It greatly surpasses standards for metallic corrosion and erosion.
Braking performance should never be compromised. AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid (BFLVCN-EA) is recommended for the hydraulic brake system. It provides excellent ABS and traction-control responsiveness with a stable viscosity over a wide temperature range, ensuring consistent pedal feel and stopping power.
For seasonal storage, AMSOIL Gasoline Stabilizer (astcn-ea) helps keep fuel fresh for up to 12 months, protecting against varnish, gum buildup, and ethanol corrosion. If the vehicle will be inactive for extended periods, AMSOIL Engine Fogging Oil (fogsc-ea) is an ideal choice to coat internal engine components and prevent rust during storage. Additional care products like AMSOIL P.i. Performance Improver (apicn-ea) can be used to restore up to 14% horsepower and clean fuel injectors, ensuring the engine performs at its peak.
About the Vehicle
The 2018 Subaru Legacy is a testament to the brand’s reputation for building reliable, safe, and capable passenger vehicles. Part of Subaru’s mid-size sedan lineup, the Legacy has long been a favorite among families, commuters, and drivers who frequent areas with challenging weather conditions. The specific model discussed here is powered by the EJ or FB series 6-cylinder engine (in this case, the EZ36D 6), which delivers a robust 256 horsepower and 247 lb-ft of torque. This powerplant is naturally aspirated, meaning it does not rely on turbochargers for boost, a design choice that generally contributes to long-term reliability and smoother power delivery.
Subaru’s Symmetrical All-Wheel Drive system is a core feature of the Legacy, standard on most trims. This layout provides inherent balance and superior traction, allowing drivers to navigate rain, snow, and light off-road conditions with confidence. The Legacy’s suspension tuning typically offers a comfortable ride quality that absorbs road imperfections well, making it an excellent choice for long highway journeys or daily city driving. The vehicle’s design focuses on practicality, offering generous cargo space in the trunk and a roomy rear seat, reinforcing its position as a family-oriented sedan.
While the Legacy is known for its durability, owners often report specific maintenance needs as the vehicle ages. One common issue in earlier models with similar 6-cylinder engines was oil consumption, which can lead to low oil levels and potential engine strain. Using a high-mileage synthetic motor oil formulated with seal conditioners and enhanced anti-wear additives can help mitigate these consumption issues and protect internal components. Another prevalent concern for flat-six engines is the need for regular coolant flushes to prevent corrosion, as the cooling system can be susceptible to degradation over time. High-quality antifreeze with superior corrosion inhibitors is essential to maintain the integrity of the radiator, hoses, and water pump. Owners also frequently address transmission shifting issues, particularly if the fluid is old or contaminated, where using a premium synthetic CVT fluid can restore smooth operation. Finally, while the all-wheel-drive system is robust, the rear differential and transfer case require periodic fluid changes to prevent wear on gears and bearings, especially for those who drive in severe conditions. Addressing these specific maintenance points ensures the 2018 Subaru Legacy continues to deliver the safety, performance, and peace of mind that owners expect from the brand.