Sierra Synthetic Blend 10W30 FC-W 4-Stroke Outboard Engine Oil, 1 Gallon – 9421CAT3
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Sierra Synthetic Blend 10W30 FC-W 4-Stroke Outboard Engine Oil – 1 Gallon | Part #9421CAT3
A synthetic-blend 10W30 engine oil formulated specifically for 4-stroke outboard engines, including Mercury 4-cycle outboards that specify 10W30. FC-W and FC-W Cat Compatible certified, this oil meets the NMMA’s requirements for water-cooled 4-stroke marine engines with and without emission catalyst systems — a standard that automotive engine oils do not meet. The gallon jug is the right size for boaters who go through oil regularly or want to keep a full season’s supply on hand.
Why 10W30 FC-W Matters for Outboards
Many 4-stroke outboard engines — particularly Mercury and Mariner models — specify 10W30 rather than the 25W40 used in most inboard and sterndrive applications. Using the correct viscosity grade is critical: too heavy an oil reduces cold-start protection and can stress the oil pump; too light an oil may not maintain adequate film strength at operating temperature. The FC-W certification ensures the oil is formulated for the marine environment, not just adapted from an automotive specification.
Key Features
- NMMA FC-W® Certified & FC-W Cat Compatible — approved for 4-stroke outboard, sterndrive, and inboard engines with and without emission catalyst systems
- Approved for Mercury 4-cycle outboards requiring 10W30 — a direct fit for Mercury and Mariner 4-stroke outboard applications
- Catalyst-safe ZDDP technology — prevents phosphorus depletion and extends emission catalyst life
- Synthetic blend base — better thermal stability and oxidation resistance than conventional mineral oil
- SAE 10W30 multi-grade — good cold-start flow with adequate high-temperature viscosity for outboard use
- Superior corrosion protection — guards internal engine components against moisture and salt exposure
- Industry-leading wear protection and deposit control — keeps engine internals clean across the full service interval
Specifications
- Viscosity: SAE 10W30
- Certification: NMMA FC-W®, FC-W Cat Compatible
- Application: 4-stroke outboard, sterndrive, and inboard marine engines; specifically approved for Mercury 4-cycle outboards requiring 10W30
- Size: 1 US gallon (3.78L)
- Part number: 9421CAT3
- Sold as: Case packs only
Parts Desk Insights
Best use case: This gallon is the go-to format for Mercury 4-stroke outboard owners who do their own oil changes and want to buy a season’s supply at once, or for service shops that stock 10W30 FC-W for Mercury outboard services. The 10W30 grade is specifically required by many Mercury 4-stroke outboards — it is not interchangeable with the 25W40 used in most inboard and sterndrive applications. For a single oil change, the Sierra Synthetic Blend 10W30 FC-W 4-Stroke Outboard Engine Oil, Qt. – 9421CAT2 is the more economical single-use option. For high-volume shop use, the Sierra 10W30 FC-W 4-Stroke Outboard Oil, 55-Gallon Drum – 94207 is available. If your engine calls for a non-catalyst-specific 10W30 FC-W oil, see the Sierra 10W30 FC-W 4-Stroke Outboard Oil, Qt. – 94202. For the OEM Mercury 10W30 synthetic blend option, see Mercury Synthetic Blend Engine Oil 10W30 – 8M0149203.
Compatibility note: Always confirm your engine manufacturer’s oil specification — viscosity grade, FC-W certification level, and any OEM approvals — before ordering. Sold in case packs; confirm case quantity at time of order.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
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Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
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