A well-maintained engine is the backbone of a smooth-running boat, and keeping up with routine oil changes is key to long-term performance. The Mercury MerCruiser Oil Filter (35-866340K01) 4-Pack is built for the job, providing top-tier filtration for GM-based MerCruiser sterndrive and inboard engines. Whether you're running a powerful V8 or a durable inline 4- or 6-cylinder, these filters help keep oil clean, reduce engine wear, and ensure reliable operation on the water.. Designed for Maximum Protection. High-Efficiency Filtration - M-Pleated filter media captures microscopic contaminants, preventing sludge buildup and maintaining oil purity.. Anti-Drain Back Valve - Keeps oil in place when the engine is off, ensuring smooth startups and preventing dry starts.. Corrosion-Resistant Housing - Heavy-duty electroplated construction stands up to the harsh marine environment, including saltwater exposure.. Why It Matters. Oil filters might be small, but they play a critical role in engine