MERCURY 4-Stroke Marine Engine Oil 25W-40 Quart — Corrosion Protection, FC-W Catalyst Compatible

MERCURY 25W-40 4‑Stroke Marine Engine Oil (1 quart) is a purpose-built lubricant that protects and stabilizes four-stroke outboard, sterndrive and inboard engines in corrosive marine environments.

Marine engines face salt, humidity, temperature swings and extended idle times that automotive oils don’t encounter. This Mercury 25W-40 formulation delivers thicker viscosity for hotter-running marine applications, a corrosion-targeted additive package, and industry certifications that meet or exceed marine OEM requirements. It’s supplied by Mercury Marine to their original equipment specifications, so it’s engineered for compatibility with Mercury, MerCruiser and many other four-stroke marine powerplants.

How does this oil guard against corrosion on and off the water?

The blend includes specialized rust and corrosion inhibitors that form a protective film on metal surfaces, reducing oxidation when the engine is wet or stored ashore. Those additives help preserve components during seasonal layups and frequent exposure to humid, salty air.

• Corrosion-inhibiting additives for external and internal protection
• Stable film formation that limits metal-to-metal contact
• Provides protection during both operation and storage

Why pick 25W‑40 for my four-stroke marine engine?

25W‑40 offers stronger viscosity at higher operating temperatures compared with lighter grades, making it well-suited for marine engines that run hot or under load. It maintains oil film thickness to protect bearings and cams while also resisting thinning from shearing and extended service intervals.

• Higher viscosity maintains oil film at elevated temperatures
• Good shear stability for longer-lasting protection
• Recommended where OEMs specify 25W‑40 for four-stroke marine use

Is this oil compatible with catalytic systems and industry standards?

Yes—this Mercury product is certified FC‑W and marked as FC‑W Catalyst Compatible, so it meets recognized marine engine performance benchmarks and is formulated to be safe with compatible exhaust emission systems. It exceeds the marine industry requirements for four-stroke oils, helping preserve warranty compliance when the correct grade is used.

• FC‑W certification for marine four‑stroke performance
• Designed to be catalyst compatible where required
• Meets or exceeds OEM warranty specifications

How does this oil support wear protection and engine longevity?

The formula combines robust base oils with anti-wear additives that reduce metal wear under load and during start-stop cycles. Consistent viscosity retention limits friction and bearing stress, contributing to extended engine life when the oil is changed at recommended intervals.

• Anti-wear chemistry to protect high-stress components
• Viscosity retention resists breakdown under heat and shear
• Manufactured to Mercury’s OEM performance and testing standards

Who is this for? Boaters, fleet operators and marine technicians who run four‑stroke outboard, sterndrive or inboard engines and need a quart-sized supply of a marine-grade 25W‑40 lubricant. It’s ideal for Mercury and MerCruiser owners looking for OEM-specified oil, anyone maintaining mixed-brand fleets that accept 25W‑40, and users who prioritize corrosion resistance, catalytic compatibility and proven wear protection. Use it where the engine manufacturer calls for 25W‑40 to maintain performance and warranty coverage.