Boating is one of the most demanding environments in which an engine can operate. Marine engines frequently run for extended periods of time at high rpm or wide-open throttle, often in corrosive saltwater. When not on the water, marine engines often sit in storage for long periods of disuse during the off-season. Recognizing these demands, Mercury Precision Lubricants® products are formulated to meet the unique needs of marine engines with specially designed additives that reduce friction and protect against engine wear and internal corrosion. The first engine manufacturer to develop oils that meet the National Marine Manufacturers Association® (NMMA) FC-W® standards for all four-stroke engines, Mercury rigorously tests its Precision Lubricants products to meet our high standards to protect your outboard, inboard or sterndrive engine and provide many years of reliable service and fun on the water. In this guide, we’ll take a closer look at the wide variety of oils and gear lubes offered in the Mercury Precision Lubricants product line to help you select the best choice for your engine or gearcase.

Mercury Precision Marine Engine Oils

Two-Stroke Marine Engine Oils

Premium 2-Stroke Engine Oil is formulated to meet the needs of low- to mid-horsepower two-stroke outboard engines under general marine operating conditions. It reduces rust and corrosion of internal components and meets or exceeds all outboard and personal watercraft manufacturers’ recommendations for use of TC-W2® and TC-W3® oils in premix and oil-injected two-stroke applications.

With a higher concentration marine additive package, Premium Plus 2-Stroke Marine Engine Oil Synthetic Blend is formulated for high-horsepower two-stroke outboards, including direct fuel-injected engines. Its clean-burning formula reduces carbon build-up in exhaust systems and provides superior lubrication in premix or oil-injected two-stroke applications.

OptiMax Synthetic Blend two-stroke engine oil was developed to meet the needs of Mercury OptiMax® and direct fuel-injected (DFI) two-stroke outboard engines. It provides maximum protection for OptiMax and DFI engines, outperforming other oils by combining a modified base stock blend with a synthetic additive package that provides superior resistance to piston scuffing, minimizes carbon build-up and helps maintain engine top-end speed and acceleration.

Four-Stroke Marine Engine Oils: Good, Better, Best

10W-30 Mineral 4-Stroke Marine Engine Oil provides outstanding lubricity for internal engine components to reduce wear, scuffing and scoring for improved long-term reliability, making it a good choice for Mercury and other brand four-stroke outboard engines. It contains advanced corrosion inhibitors and is FC-W® and FC-W Catalyst Compatible®.

10W-30 Synthetic Blend 4-Stroke Marine Engine Oil offers all the features and benefits of mineral-based oil along with industry-leading shear strength and corrosion inhibitors for better corrosion resistance and wear protection. It’s FC-W and FC-W Catalyst Compatible and recommended for all brands of four-stroke outboards.

10W-30 Full Synthetic 4-Stroke Marine Engine Oil contains 45 percent more dispersants, 24 percent more detergents and 49 percent more anti-wear additives than the synthetic blend. Developed to eliminate thermal breakdown under extreme rpm, temperatures and loads, it provides the best wear and corrosion prevention for any engine, especially those operating at maximum output and high temperatures for extended periods of time.

25W-40 Mineral 4-Stroke Marine Engine Oil provides excellent resistance against wear and corrosion along with industry-leading shear strength and viscosity retention. It’s FC-W and FC-W Catalyst Compatible and exceeds all marine industry oil requirements to help maintain peak engine performance and reliability.

25W-40 Synthetic Blend 4-Stroke Marine Engine Oil meets the stringent requirements of high-performance Mercury outboard models and other brand engines. It provides outstanding shear strength and viscosity stability for better bearing protection and superior corrosion prevention.

25W-50 Synthetic Blend 4-Stroke Marine Engine Oil is formulated with additives designed to maintain performance under high-heat and high-rpm conditions. It stays in grade under the most extreme conditions to ensure proper lubrication in a wide temperature range and is recommended for use in all Mercury Racing® FormulaRace and Verado® four-stroke outboards as well as non-catalyzed high-horsepower four-stroke marine engines.

Mercury Precision Lubricants Diesel Engine Oil

Formulated for all marine diesel engines, including Mercury, MerCruiser® and D-Tronic, 15W-40 Heavy Duty Diesel Engine Oil helps control the formation of sludge and varnish deposits in high-stress applications to protect diesel emissions systems, diesel particulate filters and Selectively Catalytic Reduction Systems. It also provides excellent shear stability to protect internal engine components against corrosion and wear.

5W-30 Full Synthetic Turbocharged Direct Injection Diesel Engine Oil resists thermal breakdown and oxidation under extreme conditions to optimize Turbocharged Direct Injection (TDI) diesel engine performance in marine applications. It protects anti-pollution systems, increases the life of diesel particulate filters (DPF) and provides outstanding wear and corrosion prevention to help extend engine life.

Mercury Precision Gear Lubes

Mercury 80W-90 Premium Gear Lube is recommended for gearcases for outboards below 75 horsepower. It outperforms automotive gear oil in marine applications by providing maximum protection against excessive wear in the presence of water and helps prevent corrosion and pitting.

SAE 90 High-Performance Gear Lube was engineered to extend gear life in high-speed and high-horsepower sterndrive and outboard gearcase applications. It contains extreme pressure synthetic additives to protect gears from metal-to-metal contact and provide excellent protection against corrosion and excessive wear.

85W-90 Extreme Performance Gear Lube is recommended for use in racing, high-performance and extreme-duty gearcase applications.