Seachoice 50-21004 Full-Flow Oil Filter – 20 Micron | Mercury & Mariner Outboard
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Seachoice 50-21004 Full-Flow Oil Filter – 20 Micron
Part Number: 50-21004 | SKU: 50-21004 | UPC: 719249210049
The Seachoice 50-21004 is a 20-micron full-flow spin-on oil filter for selected Mercury and Mariner 4-stroke outboard engines. It crosses directly to Sierra 18-7914 and to multiple Mercury and Quicksilver OEM filter numbers. Built with high-efficiency cellulose filter media, an epoxy-coated corrosion-resistant canister, reinforced body construction, heavy-duty end-cap seals, and an anti-drain-back valve, it meets or exceeds original equipment filtration requirements for applicable Mercury outboard applications.
Key Specifications
- Filtration: 20 micron
- Filter type: Full-flow spin-on
- Thread: 20 mm x 1.5
- Filter media: High-efficiency cellulose
- Anti-drain-back valve: Yes
- Canister: Epoxy-coated reinforced steel
- End-cap seals: Heavy-duty
- Manufactured in an ISO/TS 16949 certified facility
Compatible Applications
- Mercury 25 HP 4-stroke carbureted outboards, 2006 and earlier
- Mercury 30 HP 3-cylinder 4-stroke outboards, 2005 and earlier
- Mercury 40–60 HP 4-stroke outboards, 1998 and newer (selected configurations)
- Mercury 75–115 HP 4-stroke outboards (selected serial number ranges — verify before ordering)
- Mariner 4-stroke outboards specifying the listed Mercury OEM filter numbers
- Other Mercury and Mariner 4-stroke applications cross-referencing Sierra 18-7914
Fitment Note: Mercury uses several similar-looking filters across its 4-stroke outboard lineup. Always confirm fitment by matching the existing filter’s OEM part number or the Sierra 18-7914 cross-reference. Confirm by engine model, model year, and serial number — do not order by appearance alone.
Service Interval
Replace at every scheduled engine oil service. Follow Mercury’s recommended interval for your specific outboard model — typically every 100 hours or once per season, whichever comes first.
Installation Notes
- Remove the old filter and confirm the old gasket has come away with it — a retained gasket will cause an oil leak
- Clean the filter mounting surface
- Lightly coat the new filter gasket with fresh engine oil before threading it on
- Tighten by hand plus ¾ turn, or per Mercury service specification — do not over-tighten
- Run the engine and inspect for leaks before returning to service
Cross-Reference Part Numbers
- Seachoice: 50-21004 / 21004
- Sierra: 18-7914
- Mercury: 35-822626K04, 35-822626T2, 35-877768K01, 35-8M0008397, 35-8M0064104
- Mercury / Quicksilver: 35-822626Q04, 35-822626Q2
Related Products
- Sierra 7914 4-Cycle Outboard Oil Filter — Sierra OEM-equivalent filter this unit replaces
- Sierra 18-7913 4-Cycle Outboard Oil Filter – Mercury & Honda
- Seachoice 50-21011 Full-Flow Oil Filter – 20 Micron — Mercury FourStroke & Yamaha 69J-series filter
- Seachoice 50-21001 Full-Flow Oil Filter – 20 Micron — MerCruiser, Volvo Penta & OMC sterndrive filter
- Seachoice 50-21018 Full-Flow Oil Filter – 20 Micron — Yamaha 4-stroke outboard filter
Parts Desk Insights
Best Use Case: Routine oil and filter changes on Mercury and Mariner 4-stroke outboards in the 25–115 HP range that call for the Sierra 18-7914 or Mercury 35-822626 / 35-8M0064104 filter family. This is a high-volume service filter for a broad range of popular mid-size Mercury 4-stroke outboards, making it a practical stock item for dealers and boaters on a regular maintenance schedule.
Common Issues: Mercury uses multiple similar-looking spin-on filters with different thread specs and internal configurations across model years and HP ranges — the most common ordering error is choosing the wrong filter by appearance. The safest confirmation method is to match one of the OEM Mercury part numbers listed above, or the Sierra 18-7914 cross-reference, against what is currently on the engine. Always confirm by model year and serial number for engines at the edge of the horsepower ranges listed.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
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.
To qualify for a return:
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:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.