Mercury 4-Stroke Full Synthetic Marine Engine Oil – 25W-40, 1L | 8M0078641

Mercury 4-Stroke Full Synthetic Marine Engine Oil – SAE 25W-40, 1L

Protect your Mercury 4-stroke engine with this genuine OEM full synthetic marine engine oil. The full synthetic formula delivers superior thermal stability, oxidation resistance, and wear protection compared to conventional and synthetic-blend oils — making it the right choice for high-output engines, extended service intervals, or demanding operating conditions. Includes marine-specific corrosion inhibitors and shear-stability additives engineered for both saltwater and freshwater environments.

Part Details

• Part Number: 8M0078641
• Mercury Reference: 92-8M0078641
• Brand: Mercury Marine
• Product Type: 4-Stroke Marine Engine Oil – Full Synthetic
• Viscosity: SAE 25W-40
• Container Size: 1 Litre
• Certification: NMMA FC-W and FC-W Catalyst Compatible
• Condition: New OEM

Compatible Applications

• Mercury FourStroke outboards – 2.5 HP through 400 HP
• Mercury Pro XS FourStroke outboards
• Mercury Verado FourStroke outboards
• MerCruiser 3.0L, 4.3L V6, 5.0L V8, 5.7L V8, 6.2L V8, 7.4L V8, 8.2L V8 sterndrives and inboards
• Any 4-stroke marine engine where SAE 25W-40 full synthetic is specified — always confirm in your owner's manual

Key Features

• Full synthetic formula – superior thermal stability and oxidation resistance vs. conventional or synthetic-blend oils
• FC-W and FC-W Catalyst Compatible certified – safe for catalyst-equipped engines
• Advanced marine corrosion protection – enhanced inhibitors for saltwater and humid environments
• Shear stability – maintains viscosity under sustained high-RPM and heavy-load operation
• Extended drain capability – full synthetic base resists thermal breakdown longer than conventional oils

Service Interval

Change engine oil and filter at the interval specified in your engine owner's manual — typically every 100 hours or annually, whichever comes first. Full synthetic oil may support extended drain intervals on some engines; always follow Mercury's published guidance for your specific model and serial number range.

Technical FAQ

• What's the difference between 8M0078641 and 8M0078639? Both are SAE 25W-40 Mercury marine oils. 8M0078639 is a synthetic blend; 8M0078641 is full synthetic. Full synthetic offers better thermal stability and oxidation resistance.
• What's the difference between 8M0078641 and 8M0078642? Same full synthetic oil — 8M0078641 is the 1L bottle; 8M0078642 is the 4L jug.
• Can I use automotive synthetic oil instead? No. Automotive oils lack the marine-specific corrosion inhibitors required for boat engines and can void your warranty.
• Is this FC-W Catalyst Compatible? Yes — safe for engines equipped with catalytic converters.
• What if my engine specifies 10W-30? Use the viscosity in your owner's manual. See the Mercury 10W-30 Engine Oil – 1L (8M0078637) for that grade.

Also Available

• Mercury 4-Stroke Full Synthetic Oil – 4L (8M0078642)
• Mercury 4-Stroke Synthetic Blend Oil – 1L (8M0078639)
• Mercury 4-Stroke Synthetic Blend Oil – 4L (8M0078640)
• Mercury 25W-50 High Performance Oil – 1 Qt (8M0078013)
• Mercury 10W-30 Engine Oil – 1L (8M0078637)
• Mercury 10W-30 Engine Oil – 4L (8M0078638)

Parts Desk Insights

The full synthetic 8M0078641 is the right call when an engine sees hard use, extended service intervals, or operates across a wide temperature range — the full synthetic base resists thermal breakdown and oxidation significantly better than the synthetic-blend 8M0078639. The most common customer question is whether any 25W-40 marine oil is interchangeable: the viscosity matches, but full synthetic and synthetic-blend oils have different additive packages and drain-interval characteristics — if the service manual specifies full synthetic, use full synthetic. The 1L bottle is best suited for top-ups or smaller single-cylinder engines; for a full oil change on most Mercury 4-stroke outboards or MerCruiser sterndrives, the 4L jug (8M0078642) is the more practical purchase.