The 1998 Subaru Impreza with the 2.5L EJ25D engine is a machine designed for longevity, but its performance relies heavily on the quality of fluids you use. Subarus from this era are known for their flat-four boxer engines, which generate heat in a unique way due to the horizontally opposed piston layout. Using high-quality synthetic motor oils and oil filters is essential to manage these temperatures, reduce sludge buildup, and ensure smooth operation for the transmission and differential systems. Proper fluid maintenance not only protects expensive internal components but also helps maintain fuel efficiency and drivability over the vehicle’s lifespan.
Recommended AMSOIL Products
- AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil – This premium oil is our top choice for the 1998 Impreza, offering superior protection against horsepower loss and wear for up to 25,000 miles or one year. Its enhanced additive package handles the thermal stress of the boxer engine exceptionally well.
- AMSOIL Extended-Life 5W-30 100% Synthetic Motor Oil – An excellent choice for drivers seeking a balance of performance and extended service intervals. It provides up to 20,000 miles of protection and features superior cleaning power to keep the engine running smoothly.
- AMSOIL OE 5W-30 100% Synthetic Motor Oil – Designed to outperform conventional oils while meeting OEM mileage requirements. This synthetic option fights sludge and deposits effectively, making it a reliable choice for regular maintenance.
- AMSOIL 5W-30 100% Synthetic High-Mileage Motor Oil – Specifically formulated for vehicles with over 75,000 miles, this oil boosts detergent levels and reduces sludge by 67% to help older engines perform better.
- AMSOIL Oil Filter – Engineered to provide 99% filtration efficiency at 20 microns, this filter allows for lower restriction to keep engine parts lubricated and offers greater capacity for contaminants than standard filters.
- WIX Oil Filter – A premium aftermarket option that offers improvements over original equipment manufacturer-branded filters, providing high-quality media for consistent engine protection.
The engine oil capacity for the 1998 Subaru Impreza 2.5L, including the filter, is 4.8 quarts. For optimal performance, it is important to torque the oil drain plug to between 29 and 33 foot-pounds. After refilling, always check the oil level to ensure it is within the safe operating range. Selecting the correct viscosity is critical for the EJ25D engine, and 5W-30 has been identified as the ideal grade for this application.
Protecting the Cooling System and Transmission
Subaru owners know that the cooling system is a frequent point of concern for these vehicles. The 1998 Impreza requires approximately 6.3 quarts of AMSOIL Passenger Car & Light Truck Antifreeze & Coolant. This Propylene Glycol Antifreeze and Engine Coolant is a 50/50 pre-mix formulation that exceeds OEM requirements and protects all cooling system metals, gaskets, and hoses for up to 150,000 miles or 5 years. For those who prefer a concentrated option to mix themselves, the AMSOIL Propylene Glycol Antifreeze and Engine Coolant offers similar long-term protection and is suitable for high-mileage maintenance schedules.
Transmission health is equally vital, especially given the manual and automatic variants available for this model year. The automatic transmission requires a total fill of 9.8 quarts for the 4-speed unit. The AMSOIL Signature Series Multi-Vehicle 100% Synthetic Automatic Transmission Fluid is highly recommended for its ability to withstand heavy towing, elevated temperatures, and challenging terrain. It remains fluid in sub-zero conditions and provides reserve protection during heavy use. Alternatively, the AMSOIL OE Multi-Vehicle 100% Synthetic Automatic Transmission Fluid offers excellent cold-weather performance and guards against leaks, promoting smooth, shudder-free shifts. For those with manual transmissions, the capacity is 7.4 pints.
Gear Lubricants and Differential Care
The 1998 Impreza’s all-wheel-drive system relies on high-quality gear lubricants to function correctly. The front final drive, which is used with the automatic transmission, requires 2.5 pints, while the rear differential requires 1.7 pints. For GL-5 applications above 0°C, the AMSOIL SEVERE GEAR® 80W-90 100% Synthetic Gear Lube is a robust choice. It controls thermal runaway, protects against rust and corrosion, and helps reduce operating temperatures. For colder environments or all-temperature applications, the AMSOIL SEVERE GEAR® 75W-90 100% Synthetic Gear Lube provides advanced protection against wear and contains friction modifiers specifically beneficial for limited-slip applications. These synthetic gear lubes ensure long oil, seal, and equipment life, which is crucial for maintaining the durability of the drivetrain components in this iconic Japanese import.
Brake Fluid and Essential Additives
Maintaining braking performance is critical for safety, particularly on a vehicle that may see varied weather conditions. The 1998 Impreza utilizes a hydraulic brake fluid system requiring DOT 3. The AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid provides excellent ABS and traction-control responsiveness while maintaining a stable viscosity over a wide temperature range. For those looking to optimize fuel economy and engine cleanliness, the AMSOIL P.i.® Performance Improver Gasoline Additive is a powerful tool. It restores up to 14% horsepower and cleans GDI fuel injectors to 100% flow rate after a single tank of fuel, helping to control pre-ignition knock and reduce the need for higher-octane fuel.
About the Vehicle
The 1998 Subaru Impreza represents a pivotal era in the brand’s history, solidifying its reputation for producing reliable, all-weather vehicles. Powered by the 2.5-liter EJ25D boxer engine, this model year offered a balance of everyday drivability and a spirited driving character that appealed to enthusiasts. The flat-four engine layout, with its horizontally opposed pistons, provided a low center of gravity that improved handling dynamics, making the Impreza a favorite in both urban environments and on winding roads. The introduction of the 2.5-liter engine in this generation marked a significant increase in power and torque compared to its predecessor, delivering a more robust performance experience for owners.
Subaru’s commitment to symmetrical all-wheel drive during this period set the Impreza apart from many competitors, offering superior traction in snow, rain, and uneven terrain. This capability made the vehicle particularly popular in regions with harsh winters, as well as among outdoor enthusiasts who valued reliability above all else. While the 1998 model did not feature the turbocharged WRX or the rally-bred WRX STI variants that would become legendary in subsequent years, the 2.5L Impreza laid the groundwork for the company’s future dominance in motorsports and consumer trust. Its reputation for durability and all-season confidence has kept many of these vehicles on the road decades after their initial production, serving as a testament to the engineering philosophy of the late 1990s. Owners of this vehicle often cite its straightforward mechanical layout and the inherent ruggedness of the chassis as reasons they continue to maintain and drive their Imprezas with pride.