Mercury Quicksilver Transfer Port Cover O-Ring 25-33465 | Outboard & Jet Drive

Transfer Port Cover O-Ring for Mercury & Mariner Outboards

The Mercury Quicksilver 25-33465 is an OEM transfer port cover O-ring used in select Mercury and Mariner outboard and jet-drive applications. This small-diameter sealing ring sits at the transfer port cover joint, preventing fluid or pressure loss at that assembly. As with all OEM sealing parts, it should be replaced any time the joint is opened during service — reusing a compressed or heat-cycled O-ring is a common source of repeat leaks.

Part Information

• Part Number: 25-33465
• Short Reference: 33465
• Brand: Mercury / Quicksilver
• Official Product Type: O-Ring, Transfer Port Cover
• Superseded By: 8M0215007 (current Mercury OEM replacement reference — verify availability)
• Related Cross-References: 25-54029 (see Mercury O-Ring 54029), 25-822370

Compatible Applications

• Select Mercury outboard engines (verify by model and serial number)
• Select Mariner outboard engines (verify by model and serial number)
• Select Mercury jet-drive applications where the transfer port cover O-ring is specified in the parts diagram

Fitment Note: O-rings are highly application-specific. Confirm compatibility using your exact engine model and serial number in the Mercury parts catalog before ordering. Two O-rings can look identical while differing in diameter or cross-section — part number matching is the only reliable method.

System & Diagram Position

This O-ring seals the transfer port cover — a cover plate on the engine powerhead that closes off the transfer port passage. In the Mercury parts diagram, it appears in the powerhead or cylinder block section, listed alongside the transfer port cover fasteners and related sealing components. Its position varies by engine model; always locate it in the diagram for your specific serial number range before ordering.

Dimensions

Exact dimensions are not published in available catalog data for this part number. Confirm the O-ring cross-section and inner diameter against the Mercury parts diagram or by measuring the original before ordering if the part number is unavailable.

When to Replace

• Any time the transfer port cover is removed for service
• O-ring is visibly flattened, cracked, brittle, or deformed
• Fluid or pressure leak traced to the transfer port cover joint
• Preventive replacement during a powerhead rebuild or major engine service

Installation Notes

• Clean the sealing groove and cover mating surface before installing the new O-ring
• Do not stretch or twist the O-ring during installation
• A light film of compatible lubricant (such as Quicksilver 2-4-C or equivalent) helps seat the O-ring without damage
• Confirm the O-ring is fully seated in its groove before torquing the cover fasteners
• Follow the Mercury service manual torque specification for the transfer port cover

Related Parts

• Mercury MerCruiser Quicksilver O-Ring (2.800 x .103) 54029
• Mercury MerCruiser Quicksilver O-Ring 25-31986
• Mercury MerCruiser Quicksilver O-Ring 25-32069
• Mercury Oil Filter Adaptor O-Ring 25-33756
• Mercury MerCruiser End Cap O-Ring 25-35126

Technical FAQ

Q: Is 25-33465 the same as 8M0215007?
A: 8M0215007 is the current Mercury supersession reference for this part. If 25-33465 is unavailable, 8M0215007 is the replacement to request. Confirm with the Mercury parts catalog for your engine before ordering either number.

Q: Can I measure my old O-ring and find a generic substitute?
A: Technically possible, but not recommended for engine sealing applications. OEM O-rings are made to specific durometer and material specifications for the fluid and temperature environment they seal. A generic O-ring that matches the dimensions may not hold up the same way.

Q: How do I know if this is the right O-ring for my engine?
A: Look up your engine model and serial number in the Mercury parts catalog and locate the transfer port cover section in the diagram. The part number listed there is the definitive reference — if it shows 25-33465 or 8M0215007, this is the correct part.

Parts Desk Insights

Best use case: This O-ring is the right call during any transfer port cover service on a compatible Mercury or Mariner outboard. At this price point, it should always be replaced rather than reused — the cost of a repeat teardown to fix a leak from a reused O-ring is never worth it.

Common mistakes: The most frequent mistake is ordering by appearance rather than part number. O-rings that look identical can differ by 0.5mm in cross-section or inner diameter, and that difference is enough to cause a leak or prevent proper seating. Always order by the part number shown in the diagram for your specific serial number range. A second common mistake is forgetting to check whether the supersession (8M0215007) is what's currently in stock — if 25-33465 shows as unavailable, ask for the superseding number.