10 Best Four-Cycle Marine Oils 2025 in the United States

The Quicksilver by Mercury Marine 25W-40 Marine Engine Oil is designed specifically for 4-stroke marine engines, making it a suitable choice for boat owners. Its 25W-40 viscosity ensures optimal performance, especially for high-rpm outboard motors. The oil is formulated to provide superior corrosion resistance and wear protection, which helps in maintaining peak engine performance and reliability. This is particularly beneficial for marine environments where engines face harsh conditions.

A key advantage is that the oil meets Mercury Marine original equipment manufacturer specifications, offering assurance that it is tailored for such engines. However, the product is mineral-based, not synthetic, which might be a downside for those seeking synthetic oil benefits like longer intervals between oil changes. Despite its strong performance and protection characteristics, some users might prefer a synthetic option for potentially better longevity and efficiency.

It's also worth noting that the oil is a direct replacement for Mercury Marine part number 8M0078628, ensuring compatibility for those who already use this specific part. This product is well-suited for marine engines, especially Mercury Marine outboards.

Honda Pro GN4 Motor Oil is designed specifically for four-cycle marine engines and other motorcycle engines. This product comes in a 1-gallon container and has a viscosity rating of 10W-30, which is suitable for a range of temperatures and ensures smooth operation under various conditions.

One of its main strengths is its formulation, which includes high-quality base stocks and an additive package tailored to the unique requirements of motorcycle and marine engines. This makes it robust in terms of shear resistance, viscosity stability, and cleanliness – essential for the durability and performance of modern engine technologies. The oil meets the API Service Classification standards, confirming its compliance with industry criteria for quality and performance.

It is suitable for a variety of vehicles including scooters, street motorcycles, UTVs, sport motorcycles, dirt motorcycles, adventure touring, choppers, and off-road motorcycles, making it versatile. However, it might not be the best choice for users who prefer synthetic oils, as this product appears to be conventional. Additionally, it is essential to always check OEM (Original Equipment Manufacturer) recommendations to ensure compatibility with your specific engine model. As an authorized Honda dealer product, it offers the assurance of authenticity and quality, especially for Honda engines.

The Quicksilver 10W-30 Oil Change Kit is designed specifically for 4-stroke 150hp Mercury and Mariner outboards, making it a convenient all-in-one solution for these engines. The kit includes five 1L bottles of Quicksilver 10W-30 marine engine oil, an oil filter, a drain plug seal, and a drip tray, covering all essentials for an oil change.

The viscosity rating of 10W-30 ensures good performance in varied temperatures, providing reliable protection and lubrication for your marine engine. The inclusion of advanced corrosion inhibitors in the oil formulation is a significant advantage, as it helps protect engine components from rust and wear, enhancing long-term durability. Additionally, the oil is NMMA FC-W and FC-W Catalyst Compatible, indicating it meets industry standards for marine engines and can be used in engines with catalytic converters.

This oil change kit is a practical and reliable choice for owners of 150hp Mercury and Mariner outboards, offering ease of use and comprehensive protection for the engine.