Description

Mercury MerCruiser Quicksilver 25-29439 is a genuine Mercury Marine O-ring used as a sealing ring in select Mercury, Mariner, and MerCruiser water pump housing and gear housing assemblies. Mercury references list the base part number as 29439, with GTIN / UPC 745061133464, and supporting parts diagrams identify it at the water pump housing O-ring location.

Key Features

• Genuine Mercury Marine / Quicksilver O-ring reference
• Used in supported water pump housing / gear housing assemblies
• OEM part number: 25-29439
• Base part reference: 29439
• GTIN / UPC reference: 745061133464
• Size references include approximately 1.185 in. I.D. / 30.1 mm I.D. and 0.100 in. width / 2.5 mm width
• Catalog package reference: approximately 3.00 in. x 1.50 in. x 0.20 in.

Engine Compatibility

This O-ring is shown in Mercury references across select older Mercury / Mariner outboard gear housing applications, including various 3.9 HP, 4 HP, 4.5 HP, 6 HP, 7.5 HP, 9.8 HP, 40 HP, 60 HP, 75 HP, 110 HP, and Mark-series applications depending on serial number range. Mercury where-used data also lists select MerCruiser big-block applications, including 454 MAG MPI Horizon, 7.4L MPI MIE, 8.2L MIE MPI, 454 MAG MPI Bravo, and 502 MAG MPI Bravo serial ranges.

Serial Number Fitment Notice

O-ring fitment depends on the exact engine, drive, gear housing, water pump housing, and serial number range. Always confirm compatibility using the Mercury or MerCruiser serial number and the exact parts diagram before ordering, especially because 25-29439 appears across both outboard and MerCruiser-related applications.

When This Part Needs Replacement

Replace this O-ring whenever the related water pump housing or gear housing assembly is opened, or if the original seal is flattened, cut, brittle, swollen, cracked, missing, or no longer sealing properly. Reusing an old water pump housing O-ring can lead to leakage or repeat lower-unit 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, pinching, or rolling during assembly. Confirm the diagram location before installation because this O-ring is used in multiple Mercury and MerCruiser assemblies.

Alternate/Superseded Part Numbers

• 25-29439
• 29439
• Sierra 18-7156
• Sierra 18-7156-9
• GLM 81230
• Johnson / Evinrude / OMC 309731
• Volvo Penta 3852537 — related cross-reference in supported applications

Parts Desk Insight

This O-ring is commonly tied to the water pump housing area, so it is worth replacing while the pump is already apart. The safest match is by exact parts diagram callout, since 25-29439 appears across several Mercury, Mariner, and MerCruiser applications.

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