{"title":"Yamaha 9.9-55HP 2-Stroke Outboard Engine Parts","description":"\u003csection id=\"hero\" style=\"padding:16px 0;\"\u003e\n  \u003cp\u003eThis page covers Yamaha 2‑Stroke 9.9–55HP outboard engines. Use it to find compatible parts and service information, including maintenance tips, frequently replaced items, and troubleshooting guidance. You can also browse the main Yamaha collection. Scroll to the bottom of this page to start browsing parts for this engine, and on the collection page use the “Filter \u0026amp; Sort” controls to narrow results by horsepower, year range, and part category\/section.\u003c\/p\u003e\n  \u003cp\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-outboard-parts\" style=\"display:inline-block;background:#0b57d0;color:#fff;padding:10px 14px;border-radius:6px;text-decoration:none;\"\u003eBrowse All Yamaha Parts\u003c\/a\u003e\u003c\/p\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"identify-model\" style=\"padding:12px 0;\"\u003e\n  \u003ch2\u003eHow to Identify Your 9.9–55HP Model\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003eLocate the nameplate\/serial label on the transom bracket (usually on the port side). It shows model code, serial number, and shaft length.\u003c\/li\u003e\n    \u003cli\u003eRead the model code and suffix: letters typically indicate shaft length (S=15\", L=20\"), electric start, and control type (tiller\/remote). Year codes vary by region.\u003c\/li\u003e\n    \u003cli\u003eFor 2‑Stroke models, you’ll typically see an external oil tank (oil‑injection) or premix instructions on the cowl. Carburetors are standard on these engines.\u003c\/li\u003e\n    \u003cli\u003eIf you’re between platforms, note cylinder count: 9.9–30HP are commonly 2‑cylinder; 40–55HP are commonly 3‑cylinder.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"engine-overview\" style=\"padding:12px 0;\"\u003e\n  \u003ch2\u003ePlatform Overview\u003c\/h2\u003e\n  \u003ch3\u003eSmall Twin‑Cylinder (9.9–30HP)\u003c\/h3\u003e\n  \u003ctable style=\"width:100%;max-width:860px;border-collapse:collapse;\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eFeature\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eDescription\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eConfiguration\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eInline 2‑cylinder, carbureted 2‑Stroke with premix or oil‑injection.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eCommon Models\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e9.9, 15, 20, 25, 30HP 2‑Stroke families (typical tiller and remote variants).\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eAdvantages\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eLight weight, simple maintenance, excellent portability for tenders and small skiffs.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;\"\u003eNotes\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003eCooling and ignition parts often carry over within horsepower families; verify by model code and shaft length.\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\n  \u003ch3\u003eMid‑Size Triple‑Cylinder (40–55HP)\u003c\/h3\u003e\n  \u003ctable style=\"width:100%;max-width:860px;border-collapse:collapse;\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eFeature\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eDescription\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eConfiguration\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eInline 3‑cylinder, carbureted 2‑Stroke tuned for strong mid‑range torque.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eCommon Models\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e40, 50, 55HP 2‑Stroke platforms (tiller and remote, standard and long shafts).\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eAdvantages\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eGood power‑to‑weight ratio, responsive throttle, broad propeller compatibility.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;\"\u003eNotes\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003eSome ignition, thermostat, and water pump components are shared across 40\/50\/55HP models; confirm by model tag and serial.\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"service-kits\" style=\"padding:12px 0;\"\u003e\n  \u003ch2\u003eRoutine Maintenance \u0026amp; Service Parts\u003c\/h2\u003e\n  \u003cp\u003eIntervals below are general guidelines for typical use; always follow your official Yamaha service manual for exact procedures and schedules.\u003c\/p\u003e\n  \u003ctable style=\"width:100%;max-width:980px;border-collapse:collapse;\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eItem\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eInterval*\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eRemarks\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eParts Link\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eGear oil (lower unit)\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eEvery 100 hours or annually\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eInspect for water intrusion\/metal; replace drain plug gaskets.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-lower-unit-seal-kits\"\u003eYamaha Lower Unit Seal Kits\u003c\/a\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eSpark plugs\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eInspect every 50 hours; replace ~100 hours or as needed\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eGap to spec; fouling indicates rich mixture or cold running.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/spark-plug\"\u003eSpark Plugs\u003c\/a\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eFuel filter \/ inline filter\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eInspect every 50 hours; replace seasonally\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eUse fresh fuel; add water‑separating filter for boats with built‑in tanks.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/fuel-filters-1\"\u003eFuel Filters\u003c\/a\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eWater pump impeller\/kit\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eEvery 100 hours or annually\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eCritical for cooling; replace more often in sandy\/silty water.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-water-pump-repair-kits\"\u003eYamaha Water Pump Repair Kits\u003c\/a\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eAnodes (internal \u0026amp; external)\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eInspect every 50 hours; replace when 50% depleted\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eMatch material to water type (aluminum for brackish, zinc for salt, magnesium for fresh).\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-anodes\"\u003eYamaha Anodes\u003c\/a\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;\"\u003eOil injection system (if equipped)\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003eInspect seasonally\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003eCheck remote tank screen, pump operation, and oil hoses for brittleness or air leaks; for premix, confirm correct ratio.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/hoses\"\u003eHoses\u003c\/a\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"common-parts\" style=\"padding:12px 0;\"\u003e\n  \u003ch2\u003eFrequently Used Parts Categories\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003eRoutine Service – \u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-service-maintenance-kits\"\u003eYamaha Service \u0026amp; Maintenance Kits\u003c\/a\u003e\n\u003c\/li\u003e\n    \u003cli\u003eCooling System – \u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-water-pump-repair-kits\"\u003eYamaha Water Pump Repair Kits\u003c\/a\u003e\n\u003c\/li\u003e\n    \u003cli\u003eLower Unit \u0026amp; Seals – \u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-lower-unit-seal-kits\"\u003eYamaha Lower Unit Seal Kits\u003c\/a\u003e\n\u003c\/li\u003e\n    \u003cli\u003ePropellers \u0026amp; Hardware – \u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-propellers\"\u003eYamaha Propellers\u003c\/a\u003e\n\u003c\/li\u003e\n    \u003cli\u003eIgnition \/ Electrical – \u003ca href=\"https:\/\/seasierra.com\/collections\/electrical-items\"\u003eElectrical Items\u003c\/a\u003e\n\u003c\/li\u003e\n    \u003cli\u003eFuel System – \u003ca href=\"https:\/\/seasierra.com\/collections\/fuel-filters-1\"\u003eFuel Filters\u003c\/a\u003e\n\u003c\/li\u003e\n    \u003cli\u003eCorrosion Protection – \u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-anodes\"\u003eYamaha Anodes\u003c\/a\u003e\n\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"troubleshooting\" style=\"padding:12px 0;\"\u003e\n  \u003ch2\u003eCommon Symptoms \u0026amp; Quick Checks\u003c\/h2\u003e\n  \u003ctable style=\"width:100%;max-width:980px;border-collapse:collapse;\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eSymptom\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eCheck First\u003c\/th\u003e\n        \u003cth style=\"text-align:left;border-bottom:1px solid #ddd;padding:8px;\"\u003eRelated Parts\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eWeak tell‑tale or overheat alarm\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eDebris at intake screens, worn impeller, stuck thermostat, pinched hoses.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eWater pump kit, thermostat, intake screens, gaskets, hoses.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003ePoor acceleration or power loss\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eDamaged prop, clogged fuel filter, dirty carb jets, fouled plugs.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003ePropeller, fuel filter, carburetor rebuild kit, spark plugs.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eHard starting \/ rough idle\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003ePrimer bulb, choke\/enricher operation, air leaks in fuel lines, idle mixture.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eFuel hoses, primer bulb, carburetor kit, spark plugs.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eExcessive smoke (2‑Stroke)\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eIncorrect oil ratio, stuck choke, cold‑running thermostat, oil pump misadjustment.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;border-bottom:1px solid #eee;\"\u003eThermostat, choke\/enrichener parts, hoses, carburetor kit.\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd style=\"padding:8px;\"\u003eGearcase noise or metal in oil\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003eLow\/contaminated gear oil, fishing line at prop seal, worn bearings.\u003c\/td\u003e\n        \u003ctd style=\"padding:8px;\"\u003eLower unit seal kit, drain plug gaskets, prop shaft seals.\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"faq\" style=\"padding:12px 0;\"\u003e\n  \u003ch2\u003eFAQs\u003c\/h2\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eAre parts interchangeable between different years or platforms?\u003c\/summary\u003e\n    \u003cp\u003eSome ignition, cooling, and gearcase parts interchange within the same family, but changes by year and shaft length are common. Confirm compatibility using the exact model code and serial number on your bracket plate.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhen should I replace the water pump impeller?\u003c\/summary\u003e\n    \u003cp\u003eAs a rule of thumb, replace the impeller every 100 hours or annually. In sandy or silty water, or if the engine overheated, replace sooner and inspect the wear plate and cup.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eHow often should the gear oil be changed?\u003c\/summary\u003e\n    \u003cp\u003eChange the gear oil every 100 hours or at least once per season. Check for milky color (water intrusion) or metal flakes and service seals if contamination is found.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat information do you need to confirm part compatibility?\u003c\/summary\u003e\n    \u003cp\u003ePlease provide the full model code, serial number, horsepower, shaft length (S\/L\/XL), control type (tiller or remote), and whether your engine is premix or oil‑injected. Photos of the nameplate and the part in question are very helpful.\u003c\/p\u003e\n  \u003c\/details\u003e\n\u003c\/section\u003e\n\n\u003csection id=\"cta\" style=\"padding:16px 0;\"\u003e\n  \u003cp\u003eReady to find parts by horsepower, year, and model? Browse our main Yamaha outboard collection to zero in on what fits your engine.\u003c\/p\u003e\n  \u003cp\u003e\u003ca href=\"https:\/\/seasierra.com\/collections\/yamaha-outboard-parts\" style=\"display:inline-block;background:#0b57d0;color:#fff;padding:10px 14px;border-radius:6px;text-decoration:none;\"\u003eShop Yamaha Outboard Parts\u003c\/a\u003e\u003c\/p\u003e\n  \u003cp style=\"font-size:0.95em;color:#444;\"\u003eIf you’re unsure about your model, send us a photo of the nameplate and the part you need and we’ll help verify compatibility.\u003c\/p\u003e\n\u003c\/section\u003e","products":[{"product_id":"thermostat-143-f-62-c-fits-yamaha-2-stroke-9-9-55-hp-replaces-6f5-12411-01-6f5-12411-02-6f5-12411-03","title":"60°C Thermostat for Yamaha 2-Stroke 9.9D and 15D Outboards – Replaces 6F5-12411-03","description":"\u003csection\u003e\n\u003c!-- 🔧 Table Styles (include only once per page) --\u003e\n\u003cstyle\u003e\n  .ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n  table.ss-table { width:100%; border-collapse:collapse; min-width:560px; }\n  table.ss-table th, table.ss-table td {\n    padding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top;\n  }\n  table.ss-table th {\n    white-space:nowrap;\n    word-break:normal;\n    letter-spacing:normal;\n    font-weight:600;\n    background:#f8fafc;\n  }\n  @media (max-width:480px){\n    table.ss-table th, table.ss-table td { padding:8px 10px; font-size:14px; }\n  }\n\u003c\/style\u003e\n\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cp\u003eThis \u003cstrong\u003e60°C thermostat\u003c\/strong\u003e is a replacement cooling-system component for selected Yamaha 2-stroke outboards. The company catalog identifies the confirmed applications as the Yamaha \u003cstrong\u003e9.9D\u003c\/strong\u003e and \u003cstrong\u003e15D\u003c\/strong\u003e models. It is designed to help the engine maintain its specified operating temperature during normal operation.\u003c\/p\u003e\n\u003cp\u003eThe thermostat replaces Yamaha OEM part number \u003cstrong\u003e6F5-12411-03\u003c\/strong\u003e. This is an aftermarket replacement component and is not manufactured by Yamaha.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e60°C operating-temperature rating.\u003c\/li\u003e\n  \u003cli\u003eFor selected Yamaha 2-stroke 9.9D and 15D outboards.\u003c\/li\u003e\n  \u003cli\u003eReplacement thermostat for the original cooling-system component.\u003c\/li\u003e\n  \u003cli\u003eConfirm the complete engine model and existing thermostat before ordering.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003ePart Number Reference\u003c\/h2\u003e\n\u003cp\u003eUse the following manufacturer reference to compare with the thermostat currently installed on your engine.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Part Number Reference\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth\u003eBrand\u003c\/th\u003e\n        \u003cth\u003eManufacturer Part Number\u003c\/th\u003e\n        \u003cth\u003eReference Type\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6F5-12411-03\u003c\/td\u003e\n        \u003ctd\u003eOEM replacement reference\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eEngine Compatibility\u003c\/h2\u003e\n\u003cp\u003eThe confirmed company fitment is limited to the following Yamaha 2-stroke model designations. Model suffixes, production years, and serial-number ranges can affect fitment, so compare your engine identification label and original part before purchase.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Yamaha Engine Compatibility\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n        \u003cth\u003eBrand\u003c\/th\u003e\n        \u003cth\u003eModel\u003c\/th\u003e\n        \u003cth\u003eRated HP\u003c\/th\u003e\n        \u003cth\u003eStroke\u003c\/th\u003e\n        \u003cth\u003eThermostat Rating\u003c\/th\u003e\n        \u003cth\u003eOEM Reference\u003c\/th\u003e\n      \u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e9.9D\u003c\/td\u003e\n        \u003ctd\u003e9.9 HP\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e60°C\u003c\/td\u003e\n        \u003ctd\u003e6F5-12411-03\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e15D\u003c\/td\u003e\n        \u003ctd\u003e15 HP\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e60°C\u003c\/td\u003e\n        \u003ctd\u003e6F5-12411-03\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003cdl\u003e\n  \u003cdt\u003eProduct Type\u003c\/dt\u003e\n  \u003cdd\u003eOutboard thermostat\u003c\/dd\u003e\n  \u003cdt\u003eTemperature Rating\u003c\/dt\u003e\n  \u003cdd\u003e60°C\u003c\/dd\u003e\n  \u003cdt\u003eApplication\u003c\/dt\u003e\n  \u003cdd\u003eSelected Yamaha 2-stroke 9.9D and 15D outboards\u003c\/dd\u003e\n  \u003cdt\u003eReplacement Reference\u003c\/dt\u003e\n  \u003cdd\u003eYamaha 6F5-12411-03\u003c\/dd\u003e\n  \u003cdt\u003eProduct Status\u003c\/dt\u003e\n  \u003cdd\u003eAftermarket replacement component\u003c\/dd\u003e\n\u003c\/dl\u003e\n\n\u003ch2\u003eWhat's in the Box\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e1 x Thermostat\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cstrong\u003eNote:\u003c\/strong\u003e A gasket, O-ring, seal, or other installation hardware is not listed as included in the company package information. Reuse of sealing components should be avoided unless they are confirmed to be serviceable; obtain the correct replacement seal separately when required by your engine's service procedure.\u003c\/p\u003e\n\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n  \u003cli\u003eWork only with the engine stopped and completely cool. Follow the safety procedures in the applicable Yamaha service manual.\u003c\/li\u003e\n  \u003cli\u003eVerify the engine model, thermostat orientation, and sealing arrangement before disassembly.\u003c\/li\u003e\n  \u003cli\u003eRemove the thermostat cover or housing carefully and inspect the mating surfaces for corrosion, damage, or old sealing material.\u003c\/li\u003e\n  \u003cli\u003eCompare the replacement thermostat with the removed part before installation.\u003c\/li\u003e\n  \u003cli\u003eInstall the thermostat in the correct orientation and use the correct serviceable seal or gasket for your engine.\u003c\/li\u003e\n  \u003cli\u003eReinstall the cover and fasteners evenly using the manufacturer's specified tightening procedure and torque.\u003c\/li\u003e\n  \u003cli\u003eRestore the cooling-water connections as applicable, then run the outboard in a safe water-supply arrangement and check for leaks and proper water flow.\u003c\/li\u003e\n  \u003cli\u003eStop operation immediately if the engine overheats, the cooling-water indicator is abnormal, or leakage is observed.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat is the thermostat temperature rating?\u003c\/summary\u003e\n  \u003cp\u003eThis replacement thermostat is rated at \u003cstrong\u003e60°C\u003c\/strong\u003e. Do not substitute a different temperature rating unless it is specified for your exact engine.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhich engines are confirmed for this thermostat?\u003c\/summary\u003e\n  \u003cp\u003eThe confirmed company fitment is Yamaha 2-stroke 9.9D and 15D outboards. Other Yamaha models or similar-looking engines should not be assumed compatible without matching the model designation and original part number.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat part number does this thermostat replace?\u003c\/summary\u003e\n  \u003cp\u003eThe listed Yamaha OEM replacement reference is \u003cstrong\u003e6F5-12411-03\u003c\/strong\u003e.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eDoes the package include a gasket or O-ring?\u003c\/summary\u003e\n  \u003cp\u003eThe company package information lists the product as a thermostat and does not specify an included gasket or O-ring. Check your engine's service procedure and obtain the correct seal separately if needed.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow can I avoid ordering the wrong thermostat?\u003c\/summary\u003e\n  \u003cp\u003eRead the model designation from the engine identification label, compare the existing thermostat with the product reference, and verify the 60°C rating before ordering. When model suffixes or serial-number information differ, consult the applicable service documentation.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eIs this an OEM Yamaha part?\u003c\/summary\u003e\n  \u003cp\u003eNo. This listing is for an aftermarket replacement thermostat intended to replace the referenced Yamaha component.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat are your shipping speeds and costs?\u003c\/summary\u003e\n  \u003cp\u003eTypical international transit is 5–15 days. Standard shipping is free on most orders, with expedited options available at checkout where applicable.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat is your warranty and return policy?\u003c\/summary\u003e\n  \u003cp\u003eThis product is covered by a 1-year warranty against manufacturing defects under normal use. Returns are accepted within the standard return window for unused parts in their original condition. Contact support for current policy details and return instructions.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003ch2\u003eSafety \u0026amp; Important Information\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eConfirm the exact Yamaha model designation and compare the original component before purchase.\u003c\/li\u003e\n  \u003cli\u003eDo not rely on horsepower alone to determine fitment.\u003c\/li\u003e\n  \u003cli\u003eThis is an aftermarket replacement, not an original Yamaha component.\u003c\/li\u003e\n  \u003cli\u003eUse the appropriate service manual and follow all cooling-system and hot-engine safety procedures.\u003c\/li\u003e\n  \u003cli\u003eProfessional installation is recommended if you are unsure about thermostat orientation, sealing, or cooling-system service.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eAbout Sea Sierra\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePro-Grade Standards\u003c\/strong\u003e — We supply marine replacement parts selected for dependable service in real-world applications.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFast Global Fulfillment\u003c\/strong\u003e — We offer free standard delivery to most regions, with typical transit of 5–15 days.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eManufacturer-Direct Value\u003c\/strong\u003e — We work with manufacturing partners to provide practical replacement parts at competitive prices.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/section\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":50723987718459,"sku":"24TH506","price":24.2,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/24TH506_1_dc8cb029-c6d7-4a8c-81d4-6b8e022fcc5d.jpg?v=1763039538"},{"product_id":"thermostat-fits-yamaha-2-stroke-9-9-55-hp-replaces-6f5-12411-01-6f5-12411-02-6f5-12411-03","title":"Yamaha Outboard Thermostat 60°C (140°F) – 2-Stroke 25D Application – OEM 6F5-12411-03","description":"\u003cstyle\u003e\n  .ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n  table.ss-table { width:100%; border-collapse:collapse; min-width:640px; }\n  table.ss-table th, table.ss-table td {\n    padding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top;\n  }\n  table.ss-table th {\n    white-space:nowrap;\n    word-break:normal;\n    letter-spacing:normal;\n    font-weight:600;\n    background:#f8fafc;\n  }\n  @media (max-width:480px){\n    table.ss-table th, table.ss-table td { padding:8px 10px; font-size:14px; }\n  }\n\u003c\/style\u003e\n\u003csection\u003e\n  \u003ch2\u003eProduct Details\u003c\/h2\u003e\n  \u003cp\u003eThis is an aftermarket \u003cstrong\u003eYamaha outboard thermostat rated at 60°C (140°F)\u003c\/strong\u003e. It is intended for the cooling system of select Yamaha 2-stroke outboards, including the documented 25D application. The thermostat helps regulate engine operating temperature by controlling coolant flow through the thermostat housing.\u003c\/p\u003e\n  \u003cp\u003eThe company catalog identifies Yamaha OEM reference \u003cstrong\u003e6F5-12411-03\u003c\/strong\u003e for this thermostat. It is a replacement component, not a genuine Yamaha-branded part.\u003c\/p\u003e\n  \u003cul\u003e\n    \u003cli\u003eThermostat opening temperature: 60°C (140°F).\u003c\/li\u003e\n    \u003cli\u003eFor select Yamaha 2-stroke outboard applications.\u003c\/li\u003e\n    \u003cli\u003eDesigned for installation in the engine thermostat housing.\u003c\/li\u003e\n    \u003cli\u003eVerify the exact model and service-manual specification before ordering.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eReference Numbers\u003c\/h2\u003e\n  \u003cp\u003eUse the following documented references when comparing this replacement with the part being removed.\u003c\/p\u003e\n  \u003cdiv class=\"ss-table-wrap\"\u003e\n    \u003ctable class=\"ss-table\" aria-label=\"Reference Numbers\"\u003e\n      \u003cthead\u003e\n        \u003ctr\u003e\n          \u003cth\u003eBrand or Source\u003c\/th\u003e\n          \u003cth\u003eReference\u003c\/th\u003e\n          \u003cth\u003eType\u003c\/th\u003e\n          \u003cth\u003eNotes\u003c\/th\u003e\n        \u003c\/tr\u003e\n      \u003c\/thead\u003e\n      \u003ctbody\u003e\n        \u003ctr\u003e\n          \u003ctd\u003eYamaha\u003c\/td\u003e\n          \u003ctd\u003e6F5-12411-03\u003c\/td\u003e\n          \u003ctd\u003eOEM reference\u003c\/td\u003e\n          \u003ctd\u003ePrimary reference identified in the company product record.\u003c\/td\u003e\n        \u003c\/tr\u003e\n        \u003ctr\u003e\n          \u003ctd\u003eSierra\u003c\/td\u003e\n          \u003ctd\u003e18-3625\u003c\/td\u003e\n          \u003ctd\u003eAftermarket reference\u003c\/td\u003e\n          \u003ctd\u003eListed in the Sierra catalog with Yamaha reference 6F5-12411-03.\u003c\/td\u003e\n        \u003c\/tr\u003e\n      \u003c\/tbody\u003e\n    \u003c\/table\u003e\n  \u003c\/div\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eEngine \u0026amp; Model Compatibility\u003c\/h2\u003e\n  \u003cp\u003eThe confirmed company fitment identifies a \u003cstrong\u003eYamaha 2-stroke 25D\u003c\/strong\u003e application. The company application notes also reference Yamaha 20, 25, 30, 40, C40, C50, 225, 250, S225, S250, SX225, SX250, V200, V225, VX200, VX225, VX250, and P40 models. Because the available application note does not provide complete model-year, shaft, or serial-number conditions for every reference, confirm the exact engine model and compare the original thermostat before purchase.\u003c\/p\u003e\n  \u003cdiv class=\"ss-table-wrap\"\u003e\n    \u003ctable class=\"ss-table\" aria-label=\"Engine and Model Compatibility\"\u003e\n      \u003cthead\u003e\n        \u003ctr\u003e\n          \u003cth\u003eBrand\u003c\/th\u003e\n          \u003cth\u003eModel or Application\u003c\/th\u003e\n          \u003cth\u003eStroke\u003c\/th\u003e\n          \u003cth\u003eTemperature\u003c\/th\u003e\n          \u003cth\u003eReference\u003c\/th\u003e\n          \u003cth\u003eFitment Notes\u003c\/th\u003e\n        \u003c\/tr\u003e\n      \u003c\/thead\u003e\n      \u003ctbody\u003e\n        \u003ctr\u003e\n          \u003ctd\u003eYamaha\u003c\/td\u003e\n          \u003ctd\u003e25D\u003c\/td\u003e\n          \u003ctd\u003e2-Stroke\u003c\/td\u003e\n          \u003ctd\u003e60°C (140°F)\u003c\/td\u003e\n          \u003ctd\u003e6F5-12411-03\u003c\/td\u003e\n          \u003ctd\u003eConfirmed company-record application; verify model details before installation.\u003c\/td\u003e\n        \u003c\/tr\u003e\n        \u003ctr\u003e\n          \u003ctd\u003eYamaha\u003c\/td\u003e\n          \u003ctd\u003e20; 25; 30; 40; C40; C50; 225; 250; S225; S250; SX225; SX250; V200; V225; VX200; VX225; VX250; P40\u003c\/td\u003e\n          \u003ctd\u003eNot fully specified in the application note\u003c\/td\u003e\n          \u003ctd\u003e60°C (140°F)\u003c\/td\u003e\n          \u003ctd\u003e6F5-12411-03\u003c\/td\u003e\n          \u003ctd\u003eAdditional company-listed application references. Confirm the exact year, shaft, serial range, and thermostat specification from the engine identification plate and service information.\u003c\/td\u003e\n        \u003c\/tr\u003e\n      \u003c\/tbody\u003e\n    \u003c\/table\u003e\n  \u003c\/div\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n  \u003cdl\u003e\n    \u003cdt\u003eProduct Type\u003c\/dt\u003e\n    \u003cdd\u003eMarine outboard thermostat\u003c\/dd\u003e\n    \u003cdt\u003eBrand Application\u003c\/dt\u003e\n    \u003cdd\u003eYamaha outboard\u003c\/dd\u003e\n    \u003cdt\u003eStroke\u003c\/dt\u003e\n    \u003cdd\u003e2-stroke for the confirmed 25D application\u003c\/dd\u003e\n    \u003cdt\u003eOpening Temperature\u003c\/dt\u003e\n    \u003cdd\u003e60°C (140°F)\u003c\/dd\u003e\n    \u003cdt\u003ePrimary OEM Reference\u003c\/dt\u003e\n    \u003cdd\u003e6F5-12411-03\u003c\/dd\u003e\n    \u003cdt\u003eInstallation Location\u003c\/dt\u003e\n    \u003cdd\u003eThermostat housing\u003c\/dd\u003e\n    \u003cdt\u003eFuel Type\u003c\/dt\u003e\n    \u003cdd\u003eGasoline outboard application\u003c\/dd\u003e\n  \u003c\/dl\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eWhat's in the Box\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003e1 x 60°C (140°F) outboard thermostat\u003c\/li\u003e\n  \u003c\/ul\u003e\n  \u003cp\u003eAdditional gaskets, O-rings, seals, or hardware are not specified in the company package record. Reuse only serviceable components or obtain replacement sealing parts separately according to the engine service manual.\u003c\/p\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n  \u003col\u003e\n    \u003cli\u003eAllow the outboard to cool completely and follow the safety procedures in the engine service manual.\u003c\/li\u003e\n    \u003cli\u003eDisconnect the battery if required by the engine manufacturer's service procedure.\u003c\/li\u003e\n    \u003cli\u003eLocate the thermostat housing and place a suitable drain pan beneath the work area to collect water.\u003c\/li\u003e\n    \u003cli\u003eRemove the housing cover carefully and note the orientation of the original thermostat.\u003c\/li\u003e\n    \u003cli\u003eRemove the old thermostat and inspect the housing, sealing surfaces, and related sealing components for corrosion or damage.\u003c\/li\u003e\n    \u003cli\u003eInstall the replacement thermostat in the correct orientation. Replace damaged sealing components with the exact parts specified for the engine.\u003c\/li\u003e\n    \u003cli\u003eReinstall the housing cover and tighten the fasteners to the manufacturer's specified torque.\u003c\/li\u003e\n    \u003cli\u003eRun the engine according to the service-manual procedure and check for leaks, proper water flow, and abnormal temperature warnings.\u003c\/li\u003e\n  \u003c\/ol\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhat temperature is this thermostat?\u003c\/summary\u003e\n    \u003cp\u003eThis thermostat is rated at 60°C (140°F). The 140°F rating is the correct Fahrenheit conversion of the company-listed 60°C specification; the previous 143°F description has been corrected.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWhich engine is confirmed for this part?\u003c\/summary\u003e\n    \u003cp\u003eThe company product record explicitly identifies the Yamaha 2-stroke 25D application. Other Yamaha applications are listed as additional references, but exact year, shaft, serial, and model conditions should be confirmed before ordering.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eIs this thermostat for a 4-stroke engine?\u003c\/summary\u003e\n    \u003cp\u003eNo 4-stroke fitment is confirmed for this product record. The documented 25D application is 2-stroke. Do not install this thermostat in a 4-stroke engine unless the manufacturer's parts information specifically confirms compatibility.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eDoes the package include a gasket or O-ring?\u003c\/summary\u003e\n    \u003cp\u003eThe company package record identifies the product as a single thermostat and does not specify a gasket, O-ring, or seal as included. Check the service manual and obtain the required sealing parts separately if necessary.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eHow do I know if the thermostat needs replacement?\u003c\/summary\u003e\n    \u003cp\u003ePossible symptoms include overheating, an abnormal temperature warning, poor temperature regulation, or an engine that does not reach its normal operating temperature. A weak tell-tale stream can have several causes, so inspect the complete cooling system rather than relying on that symptom alone.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eCan I install this thermostat myself?\u003c\/summary\u003e\n    \u003cp\u003eThermostat replacement may be suitable for a mechanically experienced owner with the correct tools. Always follow the engine service manual, use the specified tightening torque, and seek professional service if the housing or fasteners are corroded or damaged.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eIs this a genuine Yamaha part?\u003c\/summary\u003e\n    \u003cp\u003eNo. This is an aftermarket replacement identified for Yamaha applications. Yamaha and Sierra references are provided only for product comparison and compatibility checking.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eShipping speed and cost?\u003c\/summary\u003e\n    \u003cp\u003eWe ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.\u003c\/p\u003e\n  \u003c\/details\u003e\n  \u003cdetails\u003e\n    \u003csummary\u003eWarranty and returns?\u003c\/summary\u003e\n    \u003cp\u003eCovered by a 1-year warranty against manufacturing defects under normal use. If an issue arises, contact support with your order details. Returns are accepted within our standard window when the item is unused and in its original condition. See the applicable policy page or contact support for instructions.\u003c\/p\u003e\n  \u003c\/details\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eSafety \u0026amp; Important Information\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003eConfirm the complete engine model, year, shaft, and serial information before ordering whenever available.\u003c\/li\u003e\n    \u003cli\u003eCompare the new thermostat with the original part and verify the specified opening temperature.\u003c\/li\u003e\n    \u003cli\u003eDo not rely on horsepower alone to establish compatibility.\u003c\/li\u003e\n    \u003cli\u003eDo not use this product in a 4-stroke engine unless the manufacturer's parts information confirms it.\u003c\/li\u003e\n    \u003cli\u003eThis is an aftermarket replacement, not a genuine Yamaha component.\u003c\/li\u003e\n    \u003cli\u003eProfessional installation is recommended when the thermostat housing or sealing surfaces are damaged.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/section\u003e\n\u003csection\u003e\n  \u003ch2\u003eAbout Sea Sierra\u003c\/h2\u003e\n  \u003cul\u003e\n    \u003cli\u003e\n\u003cstrong\u003ePro-Grade Standards\u003c\/strong\u003e — We supply marine replacement parts selected for dependable fit and service in real-world conditions.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cstrong\u003eFast Global Fulfillment\u003c\/strong\u003e — Free standard delivery to most regions in 5–15 days.\u003c\/li\u003e\n    \u003cli\u003e\n\u003cstrong\u003eManufacturer-Direct Value\u003c\/strong\u003e — Fair pricing without compromising on materials or quality control.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\u003c\/section\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":50723987751227,"sku":"24TH505","price":24.2,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/24TH505_1_d379df72-cd00-41d3-b470-838b53732997.jpg?v=1763039540"},{"product_id":"thermostat-143-f-62-c-fits-yamaha-2-stroke-outboard-9-9-55-hp-replaces-6f5-12411-01-6f5-12411-02-6f5-12411-03","title":"Thermostat with Seal, 143°F (62°C) – Fits Yamaha 2-Stroke Outboards 9.9–55 HP, Replaces 6F5-12411-03-00","description":"\u003csection\u003e\n\u003cstyle\u003e\n  .ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n  table.ss-table { width:100%; border-collapse:collapse; min-width:640px; }\n  table.ss-table th, table.ss-table td { padding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top; }\n  table.ss-table th { white-space:nowrap; word-break:normal; letter-spacing:normal; font-weight:600; background:#f8fafc; }\n  @media (max-width:480px){ table.ss-table th, table.ss-table td { padding:8px 10px; font-size:14px; } }\n\u003c\/style\u003e\n\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cp\u003eThis aftermarket replacement \u003cstrong\u003ethermostat with seal\u003c\/strong\u003e is designed for selected Yamaha 2-stroke outboard engines from 9.9 HP through 55 HP. It is specified for an operating temperature of \u003cstrong\u003e143°F (62°C)\u003c\/strong\u003e and replaces Yamaha OEM part number \u003cstrong\u003e6F5-12411-03-00\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp\u003eThe thermostat helps regulate engine operating temperature by controlling coolant flow through the cooling system. Confirm the exact model, year, and original part number before ordering, because Yamaha used different thermostats across similar horsepower ranges and production years.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eAftermarket replacement thermostat for selected Yamaha 2-stroke outboards.\u003c\/li\u003e\n  \u003cli\u003e143°F (62°C) operating-temperature rating.\u003c\/li\u003e\n  \u003cli\u003eSeal included for installation.\u003c\/li\u003e\n  \u003cli\u003eReplaces Yamaha OEM part number 6F5-12411-03-00.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003ePart Number References\u003c\/h2\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Part Number References\"\u003e\n    \u003cthead\u003e\u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003cth\u003ePart Number\u003c\/th\u003e\n\u003cth\u003eReference\u003c\/th\u003e\n\u003c\/tr\u003e\u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003ctd\u003eOEM replacement reference\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eSierra\u003c\/td\u003e\n\u003ctd\u003e18-3632\u003c\/td\u003e\n\u003ctd\u003eAftermarket catalog reference for this thermostat\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eEngine \u0026amp; Model Compatibility\u003c\/h2\u003e\n\u003cp\u003eThe catalog-listed applications below are Yamaha 2-stroke outboards using the 6F5-12411-03-00 thermostat reference. Model suffixes, production years, and applications must remain together when checking fitment.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Engine and Model Compatibility\"\u003e\n    \u003cthead\u003e\n      \u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003cth\u003eModel(s)\u003c\/th\u003e\n\u003cth\u003eRated HP\u003c\/th\u003e\n\u003cth\u003eStroke\u003c\/th\u003e\n\u003cth\u003eYears\u003c\/th\u003e\n\u003cth\u003eOEM Part No.\u003c\/th\u003e\n\u003c\/tr\u003e\n    \u003c\/thead\u003e\n    \u003ctbody\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e9.9EL, 9.9ES\u003c\/td\u003e\n\u003ctd\u003e9.9\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1986–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e9.9L, 9.9S\u003c\/td\u003e\n\u003ctd\u003e9.9\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1986–1990\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e9.9M\u003c\/td\u003e\n\u003ctd\u003e9.9\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1991–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e15EL, 15ES\u003c\/td\u003e\n\u003ctd\u003e15\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1986–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e15L, 15S\u003c\/td\u003e\n\u003ctd\u003e15\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1986–1990\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003e15ML, 15MS\u003c\/td\u003e\n\u003ctd\u003e15\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1991–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC25EL\u003c\/td\u003e\n\u003ctd\u003e25\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1991–1997\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC25ML\u003c\/td\u003e\n\u003ctd\u003e25\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1993–1997\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC25MS\u003c\/td\u003e\n\u003ctd\u003e25\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1992–1997\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eCV25EL, CV25EM\u003c\/td\u003e\n\u003ctd\u003e25\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1990\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC30EL\u003c\/td\u003e\n\u003ctd\u003e30\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1991–1992\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eCV30EL\u003c\/td\u003e\n\u003ctd\u003e30\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1989–1990\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC40EL\u003c\/td\u003e\n\u003ctd\u003e40\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1991–1997\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC40MS, C40PL\u003c\/td\u003e\n\u003ctd\u003e40\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1992–1997\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC40ML\u003c\/td\u003e\n\u003ctd\u003e40\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1994–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eCV40EL\u003c\/td\u003e\n\u003ctd\u003e40\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1990\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC55EL\u003c\/td\u003e\n\u003ctd\u003e55\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1991–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eC55TL\u003c\/td\u003e\n\u003ctd\u003e55\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1993–1995\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n      \u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eCV55EL\u003c\/td\u003e\n\u003ctd\u003e55\u003c\/td\u003e\n\u003ctd\u003e2-Stroke\u003c\/td\u003e\n\u003ctd\u003e1989\u003c\/td\u003e\n\u003ctd\u003e6F5-12411-03-00\u003c\/td\u003e\n\u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\u003cdl\u003e\n  \u003cdt\u003eProduct Type\u003c\/dt\u003e\n\u003cdd\u003eThermostat with seal\u003c\/dd\u003e\n  \u003cdt\u003eApplication\u003c\/dt\u003e\n\u003cdd\u003eSelected Yamaha 2-stroke outboard cooling systems\u003c\/dd\u003e\n  \u003cdt\u003eOperating Temperature\u003c\/dt\u003e\n\u003cdd\u003e143°F (62°C)\u003c\/dd\u003e\n  \u003cdt\u003eOEM Replacement\u003c\/dt\u003e\n\u003cdd\u003eYamaha 6F5-12411-03-00\u003c\/dd\u003e\n  \u003cdt\u003eAftermarket Reference\u003c\/dt\u003e\n\u003cdd\u003eSierra 18-3632\u003c\/dd\u003e\n  \u003cdt\u003ePackage Contents\u003c\/dt\u003e\n\u003cdd\u003eOne thermostat and one seal\u003c\/dd\u003e\n\u003c\/dl\u003e\n\n\u003ch2\u003eWhat’s in the Box\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e1 × Thermostat\u003c\/li\u003e\n  \u003cli\u003e1 × Installation seal\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n  \u003cli\u003eAllow the outboard to cool completely before beginning work.\u003c\/li\u003e\n  \u003cli\u003eDisconnect the battery if the engine is equipped with an electrical starting system.\u003c\/li\u003e\n  \u003cli\u003eLocate the thermostat cover and place a drain pan beneath the work area.\u003c\/li\u003e\n  \u003cli\u003eRemove the cover carefully and note the orientation of the old thermostat.\u003c\/li\u003e\n  \u003cli\u003eRemove the old thermostat and seal, then clean the mating surfaces without scratching them.\u003c\/li\u003e\n  \u003cli\u003eInstall the replacement thermostat in the same orientation as the original and fit the included seal.\u003c\/li\u003e\n  \u003cli\u003eReinstall the cover and tighten fasteners to the torque specified in the engine service manual.\u003c\/li\u003e\n  \u003cli\u003eRun the engine in a suitable water supply, confirm normal water discharge, and check the cover for leaks.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eWhat are the symptoms of a faulty outboard thermostat?\u003c\/summary\u003e\n  \u003cp\u003eA thermostat that is stuck closed can contribute to overheating, while one that is stuck open can cause the engine to run below its intended operating temperature. Reduced performance, an abnormal temperature indication, or an engine that does not warm normally can also indicate a cooling-system problem.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eDoes the package include the seal?\u003c\/summary\u003e\n  \u003cp\u003eYes. This listing includes one thermostat and one installation seal.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eIs this an OEM Yamaha part?\u003c\/summary\u003e\n  \u003cp\u003eNo. This is an aftermarket replacement for Yamaha OEM part number 6F5-12411-03-00.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n  \u003csummary\u003eHow do I confirm fitment?\u003c\/summary\u003e\n  \u003cp\u003eMatch your complete engine model, year, stroke, and original thermostat number with the compatibility information above. Do not rely on horsepower alone, because different Yamaha engines can use different thermostat applications.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003ch2\u003eSafety \u0026amp; Important Information\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eInstall only when the engine is cool and follow the service manual for your exact model.\u003c\/li\u003e\n  \u003cli\u003eVerify the model, year, stroke, and original part number before purchase.\u003c\/li\u003e\n  \u003cli\u003eDo not operate the outboard without an adequate water supply.\u003c\/li\u003e\n  \u003cli\u003eThis is an aftermarket replacement, not an OEM Yamaha component.\u003c\/li\u003e\n  \u003cli\u003eProfessional installation is recommended when the cooling system or thermostat housing is damaged.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eAbout Sea Sierra\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eMarine Replacement Parts\u003c\/strong\u003e — Practical aftermarket components for routine marine maintenance and repair.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eFitment-Focused Listings\u003c\/strong\u003e — Compatibility information is organized by model, year, horsepower, and stroke where available.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eSupport for Your Repair\u003c\/strong\u003e — Compare the original component and service-manual information before installation.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/section\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":50723987783995,"sku":"23TH015","price":23.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/23TH015_1_1a846d8b-6d3f-400f-bdc0-29b6b79a2d9e.jpg?v=1763039541"}],"url":"https:\/\/seasierra.com\/collections\/yamaha-9-9-55hp-2-stroke-outboard-engine-parts.oembed","provider":"SeaSierra","version":"1.0","type":"link"}