MERCURY 25W-40 4‑Stroke Marine Engine Oil, 1 Quart — FC-W Certified, Catalyst Compatible

MERCURY 25W-40 4-Stroke Marine Engine Oil (1 qt, part 8M0078627) is a marine-grade motor oil formulated to protect four-stroke outboards, sterndrives and inboards from wear, corrosion and viscosity breakdown on and off the water.

Boating engines face salt, moisture and stop-start operation that automotive oils are not engineered to handle. This Mercury-labeled 25W-40 oil combines a robust base-stock blend with a targeted additive package to maintain lubricant film, resist thermal thinning, and help reduce corrosion in harsh marine environments. It meets or exceeds marine industry standards, including FC-W and FC-W Catalyst Compatible certifications, and is approved for use where 25W-40 is specified by the engine maker.

How does this oil protect engines used in saltwater and freshwater?

This formula includes corrosion inhibitors and anti-wear agents tailored for marine exposure, helping preserve metal surfaces during operation and storage. The additives form a protective layer that combats rust and pitting caused by moisture and electrolytes in seawater.

• Specialized corrosion inhibitors for on- and off-water protection
• Wear-reducing additives to extend component life
• Stabilized formulation to resist oxidation and sludge

Why choose 25W-40 for my four-stroke outboard or sterndrive?

25W-40 provides a balanced viscosity profile for many mid- to high-temperature marine operating conditions, maintaining a protective oil film at operating temperatures while offering acceptable cold-start performance where 25W cold rating is suitable. Use this grade where the engine manufacturer specifies 25W-40 to meet warranty and performance requirements.

• Maintains viscosity under load and high heat
• Compatible with Mercury, MerCruiser and other leading brands
• Recommended when engine specs call for 25W-40

Is this oil compatible with catalytic systems and industry standards?

Yes — the product is certified FC-W and marked FC-W Catalyst Compatible, indicating it complies with marine fuel and emissions-related performance benchmarks and is formulated to avoid harming catalyst systems. It also surpasses common marine warranty and manufacturer recommendations for four-stroke oils.

• FC-W certified for marine four-stroke engines
• Catalyst compatible to protect emission-control components
• Meets or exceeds OEM warranty requirements

How does Mercury ensure consistent quality in this oil?

Mercury produces this lubricant to its original equipment manufacturer specifications, using decades of marine-engine testing and manufacturing experience. Strict quality controls and blend standards help deliver repeatable viscosity, additive performance and protection across production batches.

• Formulated and produced to Mercury OEM specifications
• Backed by factory testing and marine engineering know-how
• Designed for consistency between fills and seasons

Who is this for: Boaters, professional marine technicians and owners of four-stroke outboard, sterndrive and inboard engines who need a reliable, warranty-compliant 25W-40 marine oil. It’s suited for recreational and light commercial vessels operating in both freshwater and saltwater where manufacturer guidance calls for this viscosity and FC-W certification.