{"product_id":"merc-167","title":"Mercury MerCruiser O-Ring 25-34821 | OEM Sealing Ring","description":"\u003ch2\u003eMercury MerCruiser O-Ring — Part No. 25-34821\u003c\/h2\u003e\n\u003cp\u003eThis is the genuine Mercury Marine OEM O-ring listed under part number \u003cstrong\u003e25-34821\u003c\/strong\u003e (base number \u003cstrong\u003e34821\u003c\/strong\u003e). O-rings in the Mercury and MerCruiser lineup are application-specific — they are sized and compounded for the exact sealing location called out in the parts diagram. When the diagram specifies 25-34821, this is the correct OEM replacement, not a generic substitute.\u003c\/p\u003e\n\n\u003ch2\u003ePart Details\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003ePart Number:\u003c\/strong\u003e 25-34821\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBase Number:\u003c\/strong\u003e 34821\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eType:\u003c\/strong\u003e O-Ring (OEM sealing ring)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Mercury Marine OEM\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eCompatible Applications\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUse where the Mercury, MerCruiser, or Quicksilver parts diagram specifically calls for part number 25-34821 or 34821\u003c\/li\u003e\n\u003cli\u003eConfirm fitment by engine or drive serial number, assembly location, and current Mercury parts diagram before ordering\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cem\u003eO-ring fitment must be confirmed by part number and diagram position. Similar-looking O-rings vary in inside diameter, cross-section, and compound — do not substitute by size alone.\u003c\/em\u003e\u003c\/p\u003e\n\n\u003ch2\u003eAlternate \u0026amp; Superseded Part Numbers\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e25-34821\u003c\/strong\u003e — current Mercury\/MerCruiser formatted number\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003e34821\u003c\/strong\u003e — base part number\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eWhen to Replace\u003c\/h2\u003e\n\u003cp\u003eReplace this O-ring any time the assembly it seals is disassembled for service. O-rings that have been compressed, heat-cycled, or exposed to fuel or oil should never be reused — even if they appear undamaged. Replace as a matter of course during any service that disturbs the sealing location.\u003c\/p\u003e\n\n\u003ch2\u003eInstallation Tips\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eClean the O-ring groove and mating surface before installation — debris or corrosion in the groove will prevent a proper seal\u003c\/li\u003e\n\u003cli\u003eLightly lubricate the O-ring with the appropriate Mercury-approved lubricant before installation to prevent tearing during assembly\u003c\/li\u003e\n\u003cli\u003eDo not stretch or twist the O-ring during installation\u003c\/li\u003e\n\u003cli\u003eConfirm the O-ring is fully seated in the groove before assembling the mating components\u003c\/li\u003e\n\u003cli\u003eFollow the Mercury service manual torque and assembly sequence for the specific location\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eTechnical FAQ\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eQ: Can I substitute a generic O-ring of the same size?\u003c\/strong\u003e\u003cbr\u003eA: Not recommended. Mercury OEM O-rings are compounded for compatibility with the specific fluids, temperatures, and pressures at the sealing location. A generic substitute may swell, harden, or degrade faster in marine applications, leading to leaks.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eQ: How do I find the right O-ring for my engine or drive?\u003c\/strong\u003e\u003cbr\u003eA: Look up your engine or drive serial number in the Mercury parts diagram and confirm the diagram calls for 25-34821 at the specific assembly location you are servicing. If you’re unsure, our parts team can help verify before you order.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eQ: Should I replace all O-rings in an assembly at once?\u003c\/strong\u003e\u003cbr\u003eA: Yes, when practical. If one O-ring in an assembly has failed or been disturbed, replacing all O-rings in that assembly during the same service visit is good practice — it avoids a repeat teardown if another seal fails shortly after.\u003c\/p\u003e\n\n\u003ch2\u003eParts Desk Insights\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003eBest use case:\u003c\/strong\u003e This O-ring is the right call when the parts diagram specifically calls for 25-34821 and an OEM-quality seal is needed at that location. It’s a low-cost part that belongs in any service order where the assembly is being opened — ordering it ahead of teardown avoids delays waiting for a seal to arrive mid-job.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eCommon issues:\u003c\/strong\u003e The most frequent problem is customers ordering by size rather than part number, then discovering the compound or cross-section doesn’t match the original. Always order by the number in the diagram. The second common issue is reusing the original O-ring after disassembly — a seal that has been compressed and heat-cycled may look fine but will often leak on reassembly.\u003c\/p\u003e","brand":"MERC","offers":[{"title":"Default Title","offer_id":43563854331940,"sku":"34821","price":11.84,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0743\/5799\/7604\/files\/images-2026-08-20T132720.864_728bf168-cf5a-4e64-a81d-e0bf58ea0c63.jpg?v=1787264471","url":"https:\/\/marisolmarine.com\/products\/merc-167","provider":"Marisol Marine Company","version":"1.0","type":"link"}