AMSOIL 25W-40 SYNTHETIC-BLEND MARINE ENGINE OIL

AMSOIL 25W-40 Synthetic-Blend Marine Engine Oil delivers reliable wear protection and rust defense for four-stroke marine engines that spend their lives running hard in the harshest operating environment most powerplants will ever face. It is NMMA FC-W Catalyst Compatible certified and designed specifically for the demands of marine duty, not adapted from an automotive formula.

Marine engines don't operate like car engines. A boat cruising at 30 mph holds roughly 5,000 rpm for sustained periods, while a car doing 60 mph on the highway sits around 2,000 rpm. That kind of continuous high-rpm load, combined with constant exposure to moisture, salt air, and temperature swings, creates conditions that break down conventional automotive oils and leave engine internals vulnerable to corrosion during storage. Most boats also spend weeks or months sitting idle between uses, giving moisture plenty of time to attack unprotected metal surfaces.

SHEAR-STABLE PROTECTION AT SUSTAINED HIGH RPM
Marine inboards, outboards, and stern drives spend the majority of their operating hours at or near wide-open throttle. That sustained mechanical stress shears lesser oils, thinning them out and reducing their ability to maintain a protective film on bearings, cylinder walls, and cam lobes. AMSOIL 25W-40 Synthetic-Blend Marine Engine Oil is formulated for excellent shear stability, maintaining its viscosity grade under punishing loads. The Four-Ball Wear Test (ASTM D4172) returned a scar diameter of just 0.40 mm, confirming the oil's ability to keep metal surfaces separated even under extreme pressure and temperature. A high-temperature/high-shear viscosity of 4.8 cP at 150°C (ASTM D4683) means the lubricating film holds together when it matters most.

RUST AND CORROSION INHIBITORS BUILT FOR THE WATER
Rust protection is not something motor oil does naturally. It has to be engineered in. Marine engines live in humid, wet environments where condensation forms on internal surfaces every time the engine cools down. Rust acts like sandpaper against bearings, cylinder walls, and piston rings. Aluminum pistons and other alloy components corrode. Over time, this degrades compression, reduces power output, and can cause catastrophic failure. AMSOIL 25W-40 Synthetic-Blend Marine Engine Oil is fortified with potent rust and corrosion inhibitors specifically to address the unique challenges of marine service, protecting engine internals during operation and during extended off-season storage.

LOW VOLATILITY FOR CONSISTENT PERFORMANCE
With a NOACK volatility of just 3.1% weight loss (ASTM D5800), this oil resists evaporation at high temperatures. Lower volatility means less oil consumption, more consistent viscosity over the drain interval, and fewer deposits left behind in the combustion chamber. The flash point of 254°C (489°F) and fire point of 284°C (543°F) provide a wide safety margin during sustained high-output operation.

NMMA FC-W CATALYST COMPATIBLE CERTIFIED
AMSOIL 25W-40 Synthetic-Blend Marine Engine Oil carries NMMA FC-W (CAT) certification, Registration Number FC-11825T. This certification confirms compatibility with catalytic exhaust systems found on newer four-stroke marine engines and verifies the oil has passed the National Marine Manufacturers Association's performance requirements. It is approved for use in four-stroke outboards, inboards, stern drives, and personal watercraft from manufacturers including Mercury and Mercruiser.

SPECIFICATIONS AND COMPATIBILITY
This oil meets or exceeds the following specifications:

• API SM
• NMMA FC-W Catalyst Compatible

It is a direct replacement for Mercury and Mercruiser branded 25W-40 marine oils in gasoline-fueled four-stroke applications. AMSOIL backs this product with its Warranty Secure guarantee, meaning it will not void your factory warranty.

SERVICE LIFE
For four-stroke outboard motors and personal watercraft, change oil at the engine or watercraft manufacturer-recommended interval due to the potential for fuel dilution and water contamination in these applications. For inboard and inboard/outboard (I/O) engines, change oil at two times the engine manufacturer-recommended interval, or once a year, whichever comes first.