Keeping a 1987 GMC S15 Pickup with the 2.8L inline-six running strong requires more than just basic maintenance; it demands the right lubricants to combat the wear and tear of an aging engine and drivetrain. The GM 2.8L (engine code R) is a robust powerplant, but like any vehicle from the late 80s, it benefits significantly from high-quality synthetic fluids that resist breakdown, sludge formation, and thermal degradation. Using the correct viscosity and high-performance additives ensures smoother shifting, better fuel economy, and extended component life for the transmission and transfer case.
Recommended AMSOIL Products
- AMSOIL Signature Series 10W-30 100% Synthetic Motor Oil – The top choice for maximum engine protection, this oil offers up to 25,000 miles of service and superior resistance to shear breakdown in the 2.8L engine.
- AMSOIL Extended-Life 10W-30 100% Synthetic Motor Oil – An excellent option for owners seeking a balance of cleaning power and long service intervals, guaranteeing protection for up to 20,000 miles.
- AMSOIL OE 10W-30 100% Synthetic Motor Oil – A cost-effective synthetic solution that fights sludge and deposits, providing OEM-level protection for the S15’s engine.
- AMSOIL 10W-30 100% Synthetic High-Mileage Motor Oil – Formulated specifically for engines with over 75,000 miles, this fluid reduces sludge and helps prevent leaks in older vehicles.
- AMSOIL Oil Filter – Designed to work with synthetic oils, this filter offers 99% filtration efficiency and greater capacity for contaminants to protect the engine longer.
- WIX Oil Filter – A reliable alternative featuring premium media that improves upon OEM filters, suitable for standard change intervals.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – A 50/50 pre-mix formulation providing protection up to 150,000 miles or 5 years for the cooling system.
- AMSOIL Propylene Glycol Antifreeze and Engine Coolant – A concentrated option offering extended thermal protection and excellent corrosion resistance for light trucks.
- AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Ideal for the THM700-R4 and THM180C transmissions, this fluid resists wear and remains fluid in extreme temperatures.
- AMSOIL OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – A cost-effective synthetic transmission fluid that provides excellent protection against wear for the S15’s automatic gearboxes.
- AMSOIL SEVERE GEAR® 80W-90 100% Synthetic Gear Lube – Perfect for manual transmissions and differentials, offering advanced protection against wear and rust.
- AMSOIL SEVERE GEAR® 75W-90 100% Synthetic Gear Lube – A versatile heavy-duty lube that helps control thermal runaway in demanding conditions.
- AMSOIL SEVERE GEAR® 75W-110 100% Synthetic Gear Lube – Suitable for specific high-load applications requiring a heavier viscosity grade for durability.
- AMSOIL Signature Series Multi-Vehicle 100% Synthetic Automatic Transmission Fluid – A versatile fluid suitable for various transfer cases and transmissions where a multi-vehicle specification is required.
- AMSOIL OE Multi-Vehicle 100% Synthetic Automatic Transmission Fluid – Designed for smooth shifting and leak prevention in manual and automatic applications alike.
- WIX Transmission Filter – A premium filter option that improves upon original equipment standards to keep transmission fluid clean.
- AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid – Provides excellent responsiveness and a stable viscosity for safe stopping power in all weather conditions.
- AMSOIL 100% Synthetic Multi-Vehicle Power Steering Fluid – Keeps seals soft and prevents leaks while reducing friction for quiet operation.
The engine oil capacity for the 1987 GMC S15 Pickup’s 2.8L engine is 4.5 quarts, including the filter. It is crucial to select the proper viscosity, with SAE 10W-30 being the preferred grade for most operating temperatures. When refilling, always check the oil level after the refill and torque the oil drain plug to between 15 and 20 ft/lbs. While SJ oil can be used if no other grades are available, synthetic options provide significantly better protection against horsepower loss and wear.
Transmission and Drivetrain Fluids
Maintenance of the transmission system is equally vital for the longevity of this truck. The 4-speed THM700-R4 automatic transmission has a total fill capacity of 11.2 quarts, while an initial fill requires 5 quarts. For the 3-speed THM180C, the total capacity is 5.2 quarts with 3 quarts for an initial fill. These older transmission units can benefit greatly from synthetic fluids that resist thermal breakdown, ensuring smooth shifts even under heavy towing or in extreme heat.
For manual transmissions like the CH465/MC9, which uses GL-5 spec fluid, AMSOIL SEVERE GEAR® 80W-90 100% Synthetic Gear Lube offers superior wear protection. Similarly, manual transmissions such as the MSG4A/M73 and T5 series require specific AMSOIL SEVERE GEAR® 75W-90 100% Synthetic Gear Lube. The S15 often features a transfer case, such as the NP207 or NP231 series, which requires specific lubrication. The NP207 holds 4.6 pints, while the NP231 and NP233 hold 2.1 pints. Front and rear differentials also vary by gear ratio, with the 7.25 RG requiring 2.5 pints, the 8.25 RG requiring 4.2 pints, and the 9.25 RG requiring 5.9 pints. The rear 7.5 RG differential takes 4 pints. Using AMSOIL gear lubes helps control thermal runaway and protects against rust and corrosion in these heavy-duty components.
Cooling System and Brake Fluid
The cooling system in the 1987 GMC S15 Pickup holds approximately 10.6 quarts of AMSOIL Passenger Car & Light Truck Antifreeze & Coolant. Maintaining the correct antifreeze mixture is essential to prevent overheating and corrosion in the aging engine block. AMSOIL’s Passenger Car & Light Truck Antifreeze is a phosphate-, nitrate-, and silicate-free formulation that protects all cooling system metals. For those who prefer a concentrate, the Propylene Glycol Antifreeze allows for customization and offers up to 150,000 miles of protection.
Brake safety should never be compromised. The S15 utilizes hydraulic AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid that meets DOT 3 specifications. AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid ensures excellent responsiveness and stability across a wide temperature range, protecting the braking system from moisture absorption and boiling points associated with traditional fluids. Additionally, the power steering system benefits from AMSOIL’s 100% Synthetic Multi-Vehicle Power Steering Fluid, which reduces friction and helps seals remain soft to prevent leaks, a common issue in older vehicles.
About the Vehicle
The 1987 GMC S15 Pickup was a stalwart of the compact truck segment, serving as the truck variant of the popular Chevrolet S-10. Introduced in the mid-1980s as part of GM’s “Rounded Line” refresh, the S15 represented a significant evolution from its square-body predecessors. It featured a modernized, more aerodynamic design with rounded edges that appealed to a broader demographic, including those who needed utility but preferred a smoother ride.
At the heart of the 1987 model was the 2.8L V6 engine, specifically the code [R] R configuration mentioned in service guides. This engine was known for its durability and smooth power delivery, making it a favorite for both daily driving and light hauling. The S15 was available in various trims, from the base work truck to the more luxurious SLE, offering versatility that appealed to rural landowners, urban commuters, and outdoor enthusiasts alike. The compact footprint of the S15 made it incredibly maneuverable, while its robust suspension and frame provided enough capability to handle light trails and hauling duties.
Owners of the 1987 GMC S15 often appreciate its balance of size and utility. It filled a niche between full-size trucks and subcompact cars, offering a driving position and cargo space that was practical without being cumbersome. The 2.8L V6 was a significant step up from the four-cylinder options, providing the necessary torque for highway merging and towing small trailers. Over the decades, the S15 has developed a cult following among restoration enthusiasts and classic truck lovers who value its blend of 80s styling and rugged functionality.
Despite its durability, the 1987 S15 does face some common issues that owners can mitigate with the right fluids. One frequent problem is oil leaks from the valve cover gaskets and rear main seal, which can be exacerbated by the thermal breakdown of older conventional oils. Using a high-mileage synthetic oil like AMSOIL 10W-30 100% Synthetic High-Mileage Motor Oil can help condition seals and reduce these leaks. Another issue is transmission hesitation or harsh shifting, particularly in the THM700-R4, which can result from fluid oxidation and sludge buildup over time. AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid can restore smooth shifting and extend the life of the clutch packs.
Additionally, cooling system leaks and overheating are not uncommon in vehicles of this age due to corroded radiator fins and failing water pumps. AMSOIL Propylene Glycol Antifreeze and Engine Coolant helps protect against corrosion and scaling, ensuring the cooling system remains efficient. Finally, the manual transmission synchros can wear down, leading to grinding gears, a condition that can be improved by switching to a premium synthetic AMSOIL SEVERE GEAR® 80W-90 100% Synthetic Gear Lube with superior friction modifiers. Addressing these issues with high-performance lubricants allows the 1987 GMC S15 to continue serving its owners reliably for years to come.