Maintaining the 1987 Jeep Comanche with a 4.0L inline-six requires a disciplined approach to fluid management, especially as the vehicle ages. Proper lubrication is critical for preserving engine compression, ensuring smooth shifts in the transmission, and preventing rust or corrosion in the cooling and braking systems. Because this truck has seen decades of use, the right synthetic additives can help mitigate common wear issues and extend the vehicle’s operational life.
Recommended AMSOIL Products
For the 1987 Jeep Comanche 4.0L, a 10W-30 viscosity rating is specified by the manufacturer. AMSOIL offers a range of synthetic options tailored to different maintenance needs and driving styles.
- AMSOIL Signature Series 10W-30 100% Synthetic Motor Oil – Offers superior protection against horsepower loss and wear, ideal for maximizing the engine’s longevity with extended change intervals up to 25,000 miles.
- AMSOIL Extended-Life 10W-30 100% Synthetic Motor Oil – Provides enhanced cleaning power and a guaranteed protection interval of 20,000 miles for owners who prefer a balance of economy and performance.
- AMSOIL OE 10W-30 100% Synthetic Motor Oil – A cost-effective synthetic formulation designed to fight sludge and deposits, delivering reliable engine cleanliness.
- AMSOIL 10W-30 100% Synthetic High-Mileage Motor Oil – Specifically engineered for vehicles with over 75,000 miles, featuring boosted detergents to reduce sludge by 67% and restore performance.
- WIX Oil Filter – Features premium filtration media that outperforms standard OEM filters, capturing fine contaminants to keep the oil cleaner for longer.
- WIX Air Filter – Ensures clean airflow to the engine with high-quality media, improving efficiency and protecting internal components from dust and debris.
The engine capacity for the 4.0L inline-six is 5.5 quarts when including a filter change. After refilling, always check the oil level to ensure accuracy. The oil drain plug should be torqued to 30 ft/lbs to prevent stripping or leaks.
Transmission and Transfer Case Lubrication
The 1987 Comanche often utilizes the AW4 automatic transmission. Maintaining the fluid in this unit is vital for preventing shuddering and ensuring smooth gear changes. For the automatic transmission, AMSOIL Signature Series Multi-Vehicle and AMSOIL OE Multi-Vehicle fluids resist thermal breakdown, which is common during towing or heavy off-road use. The total fill capacity for the 4-speed AW4 is 8.5 quarts, though an initial fill requires approximately 4.2 quarts. A WIX Transmission Filter is recommended to replace the old unit during a service, ensuring clean fluid flow through the valve body.
- AMSOIL Signature Series Multi-Vehicle 100% Synthetic Automatic Transmission Fluid – Designed to withstand heavy towing and high temperatures, this fluid maintains fluidity in sub-zero conditions.
- AMSOIL OE Multi-Vehicle 100% Synthetic Automatic Transmission Fluid – Excellent for reducing wear and sludge while guarding against leaks, promoting shudder-free shifts.
- AMSOIL Torque-Drive 100% Synthetic Automatic Transmission Fluid – Provides long life by fighting thermal and oxidative degradation, extending the service interval significantly.
- WIX Transmission Filter – A high-efficiency filter that traps contaminants, ensuring the transmission valve body operates smoothly.
If the Comanche is equipped with a manual transmission (AX-5 or BA), the capacity varies between 3.4 and 7.4 pints depending on the specific gear ratio and drive configuration. Manual transmissions and transfer cases require robust gear lubricants to handle the high shear forces associated with off-road articulation.
- AMSOIL SEVERE GEAR 75W-90 100% Synthetic Gear Lube – A versatile GL-5 lubricant that controls thermal runaway and protects limited-slip differentials.
- AMSOIL SEVERE GEAR 75W-140 100% Synthetic Gear Lube – Ideal for rear differentials with a 7.56 or 8.8 housing, offering superior protection against extreme pressure.
- AMSOIL 75W-90 Long Life 100% Synthetic Gear Lube – Engineered for extended service life, protecting seals and improving cold-weather shifting efficiency.
Cooling, Braking, and Power Steering
The cooling system for the 1987 Jeep Comanche holds a capacity of 12.2 quarts. Using a high-quality antifreeze is essential to prevent corrosion in the older metal components and rubber hoses common in vehicles of this era. The AMSOIL Passenger Car & Light Truck Antifreeze & Coolant is a phosphate-, nitrate-, and borate-free formulation that protects all cooling system metals.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – A 50/50 pre-mix that provides protection up to 150,000 miles or 5 years.
- AMSOIL Propylene Glycol Antifreeze and Engine Coolant – A concentrated option that requires mixing with distilled water, offering superior safety and performance.
For the braking system, the vehicle typically requires a DOT 4 fluid. Hydraulic AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid absorbs moisture over time, which lowers the boiling point and can lead to pedal sponginess or corrosion. This fluid maintains a stable viscosity and offers excellent responsiveness for ABS systems.
- AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid – Provides stable viscosity and enhanced safety for vehicles equipped with traction control or ABS.
Finally, the power steering system benefits from a synthetic fluid that reduces friction and protects seals from hardening. The AMSOIL 100% Synthetic Multi-Vehicle Power Steering Fluid is formulated to keep the pump quiet and the seals soft, preventing leaks and improving steering feel.
- AMSOIL 100% Synthetic Multi-Vehicle Power Steering Fluid – Resists heat and reduces friction, ensuring quiet and responsive steering operation.
About the Vehicle
The 1987 Jeep Comanche represents a pivotal moment in the history of American compact trucks. Launched in the mid-1980s, the Comanche was built on the robust K5 Cherokee platform but featured a shorter wheelbase and a pickup bed. This made it one of the first “compact four-wheel-drive trucks” available in the U.S. market, bridging the gap between the rugged utility of the full-size Jeep Gladiator and the nimbleness of a smaller SUV. It was designed for those who needed a capable 4×4 workhorse but lacked the space for a full-size truck in a garage or driveway.
Under the hood, the 1987 model year offered the legendary 4.0L inline-six engine, known internally as the “Power-Tech” predecessor. This engine was a direct descendant of the AMC 258 cubic inch unit, but significantly improved with a higher output and better reliability. The 4.0L became famous for its immense low-end torque and incredible durability, capable of running with minimal maintenance in harsh conditions. It was a simple, cast-iron beast that delivered power reliably regardless of the terrain, whether navigating a dirt road or towing a small boat.
Owners of the 1987 Comanche often appreciate its unique blend of capabilities. It shares the same chassis architecture as the Cherokee XJ, meaning it retains the legendary suspension articulation and rugged frame rails of the Jeep. This platform allows for extensive aftermarket modifications, making it a favorite among off-road enthusiasts who customize them for rock crawling or overlanding. The shorter length makes it more maneuverable in tight trails compared to larger trucks, while the 4.0L engine provides the torque necessary to tackle steep inclines without stalling.
However, keeping a 35-year-old vehicle on the road presents specific challenges. As the vehicle ages, certain wear points become more apparent. Here are four common issues that using AMSOIL synthetic lubricants can help mitigate:
- Valve Train Noise and Wear – The 4.0L engine is robust, but over time, the hydraulic lifters can develop a distinct “ticking” noise due to oil sludge buildup or valve train wear. Switching to AMSOIL 10W-30 100% Synthetic High-Mileage Motor Oil with their enhanced anti-wear additives can help quiet the valvetrain and clean existing deposits, restoring smoother operation.
- Automatic Transmission Shuddering – The AW4 automatic transmission is known to shudder or slip as the clutch plates wear down or the fluid breaks down under heat. Using a synthetic ATF like AMSOIL Signature Series Multi-Vehicle or AMSOIL Torque-Drive can help maintain proper friction coefficients, smooth out the shifts, and potentially extend the life of the transmission components.
- Seal and Hose Leaks – Older rubber components, such as valve cover gaskets, oil pan seals, and AMSOIL Propylene Glycol Antifreeze hoses, tend to harden and shrink over decades of heat cycles. Synthetic fluids contain specific additives that help keep rubber seals supple. Using AMSOIL 100% Synthetic Multi-Vehicle Power Steering Fluid and AMSOIL 10W-30 100% Synthetic High-Mileage Motor Oil can reduce the rate of seal hardening, slowing the onset of oil or coolant leaks.
- Differential Whine and Gear Wear – The front and rear differentials on the Comanche are subject to high stress, especially when used off-road. Standard gear oils can sometimes fail to provide sufficient protection against the extreme pressures of metal-to-metal contact in aging gears. AMSOIL SEVERE GEAR 75W-90 100% Synthetic Gear Lube and AMSOIL SEVERE GEAR 75W-140 100% Synthetic Gear Lube offer superior film strength and thermal stability, helping to prevent gear whine and reduce wear on the ring and pinion gears.
With its combination of rugged engineering and versatile performance, the 1987 Jeep Comanche remains a beloved icon for truck enthusiasts. By selecting the right synthetic lubricants for this specific vehicle, owners can ensure that the iconic 4.0L engine continues to perform reliably for years to come.