Description

Mercury MerCruiser Quicksilver 25-20863 is a genuine Mercury Marine O-ring used as a sealing ring in select Mercury, Mariner, and MerCruiser assemblies. Mercury parts references list the base manufacturer part number as 20863, with GTIN / UPC 745061130234. Cross-reference data commonly identifies this O-ring as 2-5/8 in. I.D. x 2-7/8 in. O.D. x 1/8 in. width, and it is also associated with thermostat and powerhead gasket service applications on supported engines.

Key Features

• Genuine Mercury Marine / Quicksilver O-ring reference
• OEM part number: 25-20863
• Base part reference: 20863
• Size reference: 2-5/8 in. I.D. x 2-7/8 in. O.D. x 1/8 in. width
• GTIN / UPC reference: 745061130234
• Commonly included in powerhead gasket set applications for select 45 Jet, 50 HP, 55 HP, and 60 HP 3-cylinder Mercury / Mariner outboards
• Catalog package reference: approximately 3.00 in. x 3.00 in. x 0.25 in.

Engine Compatibility

This O-ring is shown in Mercury references across select older Mercury / Mariner outboard applications, including 4.5 HP, 7.5 HP, 45 / 4.5 one-cylinder, 75 HP, 450, 500, and other listed serial-number ranges. It is also cross-referenced in Sierra powerhead gasket set applications for 45 Jet, 50 HP, 55 HP, and 60 HP 3-cylinder Mercury / Mariner outboards.

Serial Number Fitment Notice

O-ring fitment depends on the exact engine model, component group, thermostat or powerhead location, and serial number range. Always confirm compatibility using the Mercury or MerCruiser serial number and the exact parts diagram before ordering.

When This Part Needs Replacement

Replace this O-ring whenever the related assembly is opened, or if the original seal is flattened, cut, swollen, hardened, cracked, missing, or no longer sealing properly. Reusing an old compressed O-ring can lead to leaks and repeat service.

Installation Notes

Clean the O-ring groove and mating surface before installation. Lightly lubricate the O-ring with the service-manual-approved lubricant where specified, and make sure it seats evenly without twisting, stretching, pinching, or rolling during assembly. Confirm the exact diagram location before installation because this O-ring appears in multiple Mercury and Mariner assemblies.

Alternate/Superseded Part Numbers

• 25-20863
• 20863
• GLM 82310
• Sierra 18-7152
• AM25-80863
• Mercury / Mariner 25-815460 — related cross-reference in supported applications

Parts Desk Insight

This O-ring is best matched by size, part number, and diagram location. It appears in more than one Mercury / Mariner service area, so using the exact serial-number diagram is safer than matching by horsepower or appearance alone.

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