258M0214974 Mercury MerCruiser O-Ring | Genuine Quicksilver OEM Part

🔧 Product Description

Genuine Quicksilver Gear Housing Cover O-Ring - Part Number: 25-8M0214974

A genuine Quicksilver large-section O-ring used in selected Mercury and Mariner gear-housing, extension and cover assemblies.

The O-ring has an approximate 3.609-inch inside diameter with a 0.139-inch cross-section. It seals the mating housing or cover joint to retain lubricant and exclude water.

⚙️ Key Features

• Genuine Quicksilver OEM O-ring

• Correct current Mercury part number 25-8M0214974

• Approximate size: 3.609-inch ID x 0.139-inch section

• Supersedes 25-861844 and 785-97386

• Used in selected mid- and high-horsepower gearcases

🔄 Supersession & Cross Reference

OEM Supersession Chain:

• 25-8M0214974 → Supersedes 25-861844

• 25-861844 → Supersedes / replaces 785-97386

• 785-97386 earlier OEM O-ring reference

OEM / Related Numbers:

• 25-8M0214974

• 8M0214974

• 258M0214974

• 25-861844

• 861844

• 785-97386

• Size: 3.609 x 0.139 inch

Aftermarket / Verified Equivalents:

• No aftermarket equivalent

🚤 Compatibility

Commonly used on:

• Mercury and Mariner gear-housing cover and extension assemblies

• Large O-ring sealing locations in mid- and high-horsepower lower units

Typically suits:

• Engine models:

• Mercury 65HP through 90HP gear-housing applications using the 861844 O-ring

• Mercury 100HP 4-cylinder

• Mercury 115HP 4-cylinder

• Mercury 125HP 4-cylinder

• Mercury 115HP extension-kit and lower-unit assemblies

• Mercury 3.0L EFI and DFI lower-unit assemblies using the corresponding large housing O-ring

• Mercury / Mariner gearcases whose parts diagram specifies a 3.609 x 0.139-inch O-ring

• HP Range: Approximately 65HP - 250HP where specified

• Engine Type: Mercury / Mariner two-stroke, EFI and DFI outboard

• System Type: Gear-housing cover / extension sealing O-ring

🔌 Function

The O-ring seals the housing joint, retaining lower-unit lubricant and preventing water from entering the gear and bearing cavity.

Common signs of failure:

• Gear lubricant leaking from the housing joint

• Milky or water-contaminated gear oil

• Gearcase fails pressure or vacuum testing

• O-ring flattened, pinched or cut

• Corrosion in the O-ring groove

📦 Condition

• Genuine Quicksilver part

• Brand new

• Supplied in original or equivalent packaging