The 2018 Mercedes-Benz GLC350E is a sophisticated plug-in hybrid that pairs a 2.0-liter turbocharged four-cylinder engine with an electric motor to deliver a balanced mix of performance and fuel efficiency. Owning this vehicle requires a maintenance regimen that respects its advanced engineering, particularly regarding the engine’s high-performance demands and the specific cooling requirements of its hybrid powertrain. Proper lubrication ensures the turbocharger operates at peak efficiency while protecting internal components from the high thermal loads associated with both combustion and electric drive systems.
Recommended AMSOIL Products
- AMSOIL 5W-40 FS 100% Synthetic European Motor Oil – This oil is specifically designed for the unique demands of gasoline, diesel, and hybrid European vehicles, featuring a precise blend of synthetic base oils and premium additives.
- AMSOIL 0W-40 FS 100% Synthetic European Motor Oil – An excellent choice for maintaining optimal flow and protection in extreme temperatures, ensuring the engine remains fluid even when the vehicle is starting in cold conditions.
- AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Withstands the rigors of heavy towing, elevated temperatures, and challenging terrain while remaining fluid in sub-zero conditions to provide reserve protection during heavy use.
- AMSOIL OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Provides superior protection against wear for the vehicle’s automatic transmission, ensuring smooth shifting and extended component life.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – A unique poly-organic acid formulation that offers protection up to 150,000 miles or 5 years, safeguarding all cooling system metals, gaskets, and hoses against corrosion.
- AMSOIL Propylene Glycol Antifreeze and Engine Coolant – A concentrated option that requires mixing with distilled water, providing protection up to 150,000 miles or 5 years with greatly surpassed standards for metallic corrosion and erosion resistance.
- AMSOIL P.i. Performance Improver Gasoline Additive – Restores up to 14% horsepower and brings GDI fuel injectors back to 100% flow rate after just one tank of fuel, improving overall fuel economy.
- AMSOIL Gasoline Stabilizer – Helps keep fuel fresh for up to 12 months, protecting against varnish, gum buildup, and ethanol corrosion during seasonal storage.
Engine Oil and Filtration
The heart of your 2018 GLC350E is the 2.0-liter 4-cylinder engine, identified by code 274.920.9 Turbo. This engine operates under significant stress, especially given the turbocharging system which generates substantial heat. To combat this, AMSOIL recommends either the 5W-40 FS 100% Synthetic European Motor Oil or the 0W-40 FS 100% Synthetic European Motor Oil. Both products are engineered with a European formula that features a precise blend of synthetic base oils and premium additives designed specifically for gasoline, diesel, and hybrid European vehicles.
The oil capacity for the engine is 6.9 quarts when performing a change with a filter replacement. After refilling, it is crucial to check the oil level to ensure the correct quantity is present. When tightening the drain plug, a torque of 30 ft/lbs is required. Owners should remember to replace the drain plug seal to prevent future leaks. While no specific oil filter recommendation was available in the current source data, using high-quality synthetic oil significantly reduces sludge formation and extends the time intervals between maintenance, providing superior engine cleanliness compared to conventional oils.
Cooling System Maintenance
Maintaining the proper temperature is vital for the hybrid system’s longevity. The cooling system requires a specific fluid that protects all metals, gaskets, and hoses. For a complete fluid change, the capacity for the Hybrid Thermal Cooling Coolant (HTCC) is 16.9 quarts. If using the Low Thermal Cooling Coolant (LTCC), the capacity is 7.9 quarts. AMSOIL offers two primary options here: the Passenger Car & Light Truck Antifreeze & Coolant and the Propylene Glycol Antifreeze and Engine Coolant.
The Passenger Car & Light Truck Antifreeze & Coolant is a 50/50 ethylene glycol pre-mix formulation. It is phosphate-, nitrate-, nitrite-, silicate-, borate-, and amine-free, making it compatible with all other antifreeze colors. It provides protection for up to 150,000 miles or 5 years. Alternatively, the Propylene Glycol Antifreeze is a concentrated fluid that requires mixing with distilled or high-quality water. This concentrated option also offers protection for up to 150,000 miles or 5 years in passenger cars and light trucks, with greatly surpassed standards for metallic corrosion and erosion.
Transmission and Drivetrain Fluids
The 2018 GLC350E is equipped with a 724.268 7-speed automatic transmission. Proper lubrication is essential for this complex unit, especially when dealing with the torque conversion required in a hybrid setup. The total fill capacity for the automatic transmission is 9.5 quarts. AMSOIL offers two excellent choices for this application: the Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid and the OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid.
The Signature Series fluid is designed to withstand the rigors of heavy towing, elevated temperatures, and challenging terrain. It remains fluid in sub-zero temperatures and provides reserve protection during heavy use. The OE Fuel-Efficient fluid provides comparable protection against wear, ensuring the transmission shifts smoothly under all conditions. For the transfer case, the capacity is listed as unknown, with a total of 1.5 pints required for the unit. If service is required, the torque specifications are 18 ft/lbs for the drain plug and 10 ft/lbs for the fill plug. The same Signature Series or OE Fluids are recommended for the transfer case and front differential, which holds 1.3 pints.
Additional Fluids and Protectants
While the primary maintenance involves engine oil, coolant, and transmission fluid, there are other fluids and protectants that contribute to the vehicle’s health. For storage purposes, AMSOIL Gasoline Stabilizer helps keep fuel fresh for up to 12 months, preventing varnish and gum buildup and fighting ethanol corrosion. If the vehicle will be sitting for an extended period, AMSOIL Engine Fogging Oil is an excellent choice to protect internal components during storage.
For fuel system health, the P.i. Performance Improver is a powerful gasoline additive that can restore up to 14% horsepower and bring GDI fuel injectors back to 100% flow rate. It also helps prevent carbon rap and controls pre-ignition knock. For general vehicle care, products like the Heavy-Duty Metal Protector provide a long-lasting protective coating against salt and moisture, while the AMSOIL Silicone Spray helps protect rubber surfaces from cracking and drying. The High-Foam Car Shampoo and Exterior Ceramic Spray ensure the vehicle’s finish remains protected against UV rays and contaminants.
About the Vehicle
The 2018 Mercedes-Benz GLC350e represents a significant step in the brand’s evolution toward electrification, sitting as a compact luxury midsize crossover SUV. This model combines the practicality of an SUV with the efficiency of a plug-in hybrid powertrain. Under the hood lies the M274 engine, a 2.0-liter turbocharged inline-four that serves as the combustion component of the hybrid system. When paired with the electric motor, the vehicle delivers a combined system output that offers brisk acceleration without the typical fuel penalty of a large displacement engine.
Driven on the M274 platform, the GLC350e inherits the robust engineering standards of the Mercedes-Benz C-Class while offering a higher ride height and increased cargo utility. Owners often appreciate the seamless transition between electric-only driving and hybrid operation, which makes it ideal for city commuting where short trips benefit from zero-emission driving. The vehicle’s market position is firmly in the competitive segment against rivals like the BMW X3 xDrive30e and the Volvo XC60 T8, known for their strong performance and premium interiors.
The turbocharged nature of the 2.0L engine means that the vehicle is susceptible to high operating temperatures, particularly during stop-and-go traffic or aggressive driving. This thermal stress can accelerate the breakdown of lubricants. Additionally, the complex nature of the hybrid powertrain, which integrates high-voltage components with traditional drivetrain parts, requires fluids that are stable over long periods to prevent corrosion and deposit buildup. Many GLC350e owners report issues with engine knock or reduced fuel economy if lower-quality fluids are used, which is why switching to high-quality synthetic lubricants is often recommended to mitigate these common problems. The plug-in hybrid system also relies heavily on the cooling system’s integrity to manage the battery and motor temperatures, making the choice of a high-performance antifreeze critical for long-term reliability.
Owners should also be mindful of the transfer case and differential maintenance, as the all-wheel-drive system (4MATIC) adds complexity to the drivetrain. Ensuring that the transfer case fluid is free of contamination and properly lubricated prevents the wear and tear associated with the constant power transfer between the front and rear axles. By adhering to the recommended fluid specifications, GLC350e owners can maintain the vehicle’s performance characteristics and resale value for years to come.