Keeping a 2018 BMW M240I running with peak performance requires lubricants that meet the strict demands of its high-output turbocharged engine. The 3.0L inline-six B58 engine is engineered for precision, responding to throttle inputs with immediacy and delivering power efficiently. However, that same performance architecture subjects the engine and its companion transmission to higher thermal loads and stress levels than standard passenger vehicles. Using factory-standard fluids often means adhering to frequent service intervals to ensure longevity, whereas premium synthetic lubricants can extend those intervals while providing superior protection against wear, deposits, and fluid degradation.
Recommended AMSOIL Products
- AMSOIL 0W-20 LS 100% Synthetic European Motor Oil – A premium synthetic oil specifically designed for the European B58 engine, offering exceptional protection against high turbocharger temperatures and deposits.
- WIX Oil Filter – A high-efficiency filter designed to work seamlessly with the synthetic oil to capture contaminants and ensure clean oil circulation.
- AMSOIL Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – Engineered to withstand the rigors of the ZF 8-speed transmission, ensuring smooth shifts and protection under heavy loads.
- AMSOIL OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid – A cost-effective alternative that still provides superior wear protection and fluid stability for the automatic transmission.
- AMSOIL DOT 3 and DOT 4 100% Synthetic Brake Fluid – Provides a higher boiling point than conventional fluid, ensuring consistent braking performance during spirited driving.
- AMSOIL Passenger Car & Light Truck Antifreeze & Coolant – A ready-to-use 50/50 pre-mix formulation that protects the cooling system from corrosion and overheating.
- AMSOIL Propylene Glycol Antifreeze and Engine Coolant – A concentrated option that requires mixing with water, offering extended service intervals and superior heat transfer properties.
Engine Oil and Filter Specifications
The heart of the M240I is the B58 engine, a turbocharged 3.0-liter inline-six that produces significant horsepower and torque. To keep this engine healthy, the oil must maintain its viscosity under high heat and resist shear breakdown. The factory recommendation points to an SAE 0W-20 viscosity grade. For those seeking to maximize engine life and performance, AMSOIL 0W-20 LS 100% Synthetic European Motor Oil is the ideal choice. It is formulated with a unique blend of synthetic base oils and additives to meet the stringent requirements of German engineering, helping to reduce sludge formation and control piston deposits.
When changing the oil, the system requires 6.9 quarts when the filter is also replaced. It is crucial to replace the oil drain plug seal to ensure no leaks occur, and to torque the drain plug to the specified 18 ft-lbs. To complement the synthetic oil, the WIX Oil Filter (WL10342) is the recommended filtration solution. This filter utilizes premium media designed to outperform original equipment manufacturer filters, capturing microscopic wear particles that can damage the engine’s tight tolerances.
Transmission and Differential Lubrication
Power delivery in the M240I is managed by a ZF 8HP50 eight-speed automatic transmission. This transmission is renowned for its smooth shifts but operates under high thermal loads, especially during aggressive driving. Using a fluid designed for standard passenger cars may not provide sufficient thermal stability over the long term. AMSOIL offers two primary options for the automatic transmission: the Signature Series Fuel-Efficient 100% Synthetic Automatic Transmission Fluid or the OE Fuel-Efficient 100% Synthetic Automatic Transmission Fluid. The Signature Series version is engineered to withstand elevated temperatures and heavy towing, remaining fluid even in sub-zero conditions, while the OE series offers a balance of performance and cost without sacrificing the synthetic protection needed for the 8-speed gearbox. The total fill capacity for the 8-speed unit is 9.3 quarts.
While the M240I does not have a manual transmission, it is important to note that the clutch fluid system requires specific attention. BMW recommends a DOT 4 Low Viscosity fluid. AMSOIL’s 100% Synthetic DOT 3 and DOT 4 Brake Fluid is an excellent upgrade. Its high boiling point prevents vapor lock during hard braking, and its low viscosity ensures quick response times for the anti-lock braking system and traction control modules, which are critical for a performance coupe like the M240I.
Cooling System Maintenance
The B58 engine runs hot, particularly the turbocharger. Effective cooling is non-negotiable for longevity. The vehicle uses different antifreeze capacities depending on the trim level. The High-Temperature Cooling Control (HTCC) models require approximately 11.1 quarts, while the Manual Transmission models with the Heat Management System (HTCC) require 9.8 quarts. Lower trim levels (LTCC) require about 4.1 quarts.
AMSOIL offers two distinct cooling solutions. The Passenger Car & Light Truck Antifreeze & Coolant is a 50/50 pre-mixed, ethylene glycol formulation that requires no mixing and provides protection up to 150,000 miles or five years. For those who prefer a concentrated antifreeze, the AMSOIL Propylene Glycol Antifreeze and Engine Coolant offers extended protection up to 150,000 miles or five years in passenger cars, or even up to one million miles in heavy-duty applications. Both options are free of phosphates, nitrates, and silicates, making them compatible with all cooling system metals and hoses while protecting against corrosion.
Fluid Additives and Vehicle Care
To further protect the powertrain, especially in direct injection engines, AMSOIL offers fuel system maintenance products. The M240I features a GDI engine, which can be prone to carbon buildup on intake valves over time. AMSOIL P.i. Performance Improver is a gasoline additive designed to restore up to 14% of horsepower by cleaning injectors and removing carbon deposits. It is compatible with capless fuel systems and helps prevent pre-ignition knock.
For vehicle owners looking to maintain the cosmetic appearance of their M240I, AMSOIL provides a range of cleaning and detailing products. The AMSOIL Engine Degreaser is effective for removing grease from the engine bay without harsh scrubbing. For cleaning the paint, the AMSOIL Miracle Wash Waterless Wash and Wax Spray offers a protective finish without the need for a traditional hose and bucket wash. The AMSOIL Exterior Ceramic Spray adds a layer of protection against UV rays and water spotting, ensuring the vehicle looks pristine.
About the Vehicle
The 2018 BMW M240i represents a pivotal moment in the BMW compact sports car lineage. Arriving as the successor to the F22 1 Series range, the M240i moved from a 4-cylinder engine to the formidable B58 inline-six. This transition elevated the M240i from a spirited hatchback into a legitimate performance rival to vehicles significantly more expensive than it. The M240i is built on the rear-wheel-drive (or optional xDrive all-wheel-drive) LCI CLAR platform, which offers a near-perfect 50/50 weight distribution, enhancing its dynamic handling capabilities.
The 3.0-liter turbocharged engine produces around 320 to 335 horsepower, depending on the specific market and trim configuration, paired with a 6-speed or 8-speed automatic transmission. This powertrain delivers a linear surge of torque that feels responsive and engaging, making the car a joy to drive on winding roads or during spirited track days. The interior is driver-focused, with high-quality materials and ergonomic designs typical of BMW’s premium positioning. Owners of the M240i often appreciate the balance of daily usability and weekend thrills, allowing the car to serve as a primary vehicle without sacrificing performance.
However, like any high-performance machine, the M240i has specific areas that require attention as it ages. One common issue with the N20 and B-series engines in general is the potential for oil leaks at the valve cover gasket and oil filter housing gasket. While the B58 is an improvement over previous generations, high heat and thermal cycling can still degrade standard rubber gaskets over time. Premium synthetic oils like AMSOIL’s European formula are less likely to cause gasket degradation compared to conventional oils, and their superior sealability can help mitigate minor seepage issues.
Another prevalent concern for turbocharged vehicles is carbon buildup on the intake valves, particularly on direct injection engines like the B58. Since fuel is injected directly into the combustion chamber, it does not wash over the intake valves, allowing carbon to accumulate from crankcase ventilation blow-by gases. This buildup can lead to rough idling, misfires, and reduced fuel economy. Regular use of a high-quality fuel additive like AMSOIL P.i. Performance Improver can help clean these injectors and intake ports, maintaining peak engine efficiency.
Additionally, the B58 engine is known to be sensitive to oil sludge if oil changes are not performed frequently enough or with poor-quality oil. Sludge can clog the oil passages, particularly the critical variable valve timing (VVT) solenoids, leading to timing issues and rough idle. AMSOIL’s superior detergents and dispersants help keep the engine internals cleaner for longer, allowing for extended oil change intervals without risking sludge formation.
Finally, the ZF 8HP50 transmission, while robust, benefits from high-quality fluid to ensure smooth shifting as the vehicle accumulates mileage. The transmission can develop shuddering or rough shifts if the fluid degrades or becomes contaminated with clutch material. Using a synthetic transmission fluid like AMSOIL’s Signature Series helps maintain the fluid’s frictional properties and thermal stability, ensuring the transmission continues to shift seamlessly throughout the life of the vehicle. By addressing these common areas with the right lubricants, M240i owners can ensure their vehicle remains a reliable and exciting drive for years to come.