{"product_id":"thermostat-fits-yamaha-4-stroke-80-100hp-replaces-yamaha-6d9-12411-00-sierra-18-3639","title":"Thermostat – Fits Yamaha 4-Stroke 80-100HP (Replaces Yamaha 6D9-12411-00, Sierra 18-3639)","description":"\u003cstyle\u003e\n\/* Outer container allows horizontal scrolling (with iOS momentum) *\/\n.ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n\/* Base table styles *\/\ntable.ss-table { width:100%; border-collapse:collapse; min-width:640px; }\ntable.ss-table th, table.ss-table td {\npadding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top;\n}\n\/* Key: prevent wrapping, word breaks, and vertical text in headers *\/\ntable.ss-table th {\nwhite-space:nowrap; \/* Do not wrap *\/\nword-break:normal; \/* Don’t break words *\/\nletter-spacing:normal; \/* Prevent theme styles from stretching letters *\/\nfont-weight:600;\nbackground:#f8fafc;\n}\n\/* Small screen optimization *\/\n@media (max-width:480px){\ntable.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 a direct replacement \u003cstrong\u003eThermostat – Fits Yamaha 4-Stroke 80-100HP (Replaces 6D9-12411-00)\u003c\/strong\u003e, designed for reliable temperature regulation in Yamaha F100D, F100A, F100B, and F80A outboard models from 2005–2017. Maintaining the correct engine temperature is crucial for performance and fuel efficiency.\u003c\/p\u003e\n\u003cp\u003eIt serves as a direct cross-reference for Yamaha part number 6D9-12411-00 and Sierra part 18-3639.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eDesigned for direct-fit installation.\u003c\/li\u003e\n\u003cli\u003eMaintains a consistent operating temperature of 55°C (131°F).\u003c\/li\u003e\n\u003cli\u003eIncludes one thermostat ready for installation.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003ePart Number Matrix\u003c\/h2\u003e\n\u003cp\u003eUse this matrix to confirm equivalent references across OEM and aftermarket.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n\u003ctable class=\"ss-table\" aria-label=\"Part Number Matrix\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003cth\u003ePart Number\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\u003e6D9-12411-00\u003c\/td\u003e\n\u003ctd\u003eOEM Reference\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eSierra\u003c\/td\u003e\n\u003ctd\u003e18-3639\u003c\/td\u003e\n\u003ctd\u003eAftermarket replacement (compatibility unverified by Sea Sierra)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/div\u003e\n\u003ch2\u003eEngine \u0026amp; Model Compatibility\u003c\/h2\u003e\n\u003cp\u003eConfirm your engine model\/year in the table below.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n\u003ctable class=\"ss-table\" aria-label=\"Engine \u0026amp; Model 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\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\u003eF100DET\u003c\/td\u003e\n\u003ctd\u003e100\u003c\/td\u003e\n\u003ctd\u003e4-Stroke\u003c\/td\u003e\n\u003ctd\u003e2005–2014\u003c\/td\u003e\n\u003ctd\u003e6D9-12411-00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eF100L\u003c\/td\u003e\n\u003ctd\u003e100\u003c\/td\u003e\n\u003ctd\u003e4-Stroke\u003c\/td\u003e\n\u003ctd\u003e2015–2017\u003c\/td\u003e\n\u003ctd\u003e6D9-12411-00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eF100X\u003c\/td\u003e\n\u003ctd\u003e100\u003c\/td\u003e\n\u003ctd\u003e4-Stroke\u003c\/td\u003e\n\u003ctd\u003e2015–2017\u003c\/td\u003e\n\u003ctd\u003e6D9-12411-00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eF100A\u003c\/td\u003e\n\u003ctd\u003e100\u003c\/td\u003e\n\u003ctd\u003e4-Stroke\u003c\/td\u003e\n\u003ctd\u003e\u003c\/td\u003e\n\u003ctd\u003e6D9-12411-00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eF100B\u003c\/td\u003e\n\u003ctd\u003e100\u003c\/td\u003e\n\u003ctd\u003e4-Stroke\u003c\/td\u003e\n\u003ctd\u003e\u003c\/td\u003e\n\u003ctd\u003e6D9-12411-00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eYamaha\u003c\/td\u003e\n\u003ctd\u003eF80A\u003c\/td\u003e\n\u003ctd\u003e80\u003c\/td\u003e\n\u003ctd\u003e4-Stroke\u003c\/td\u003e\n\u003ctd\u003e\u003c\/td\u003e\n\u003ctd\u003e6D9-12411-00\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/div\u003e\n\u003ch2\u003eTechnical Specs\u003c\/h2\u003e\n\u003cdl\u003e\n\u003cdt\u003eProduct Type\u003c\/dt\u003e\n\u003cdd\u003eMarine Engine Thermostat\u003c\/dd\u003e\n\u003cdt\u003eInstallation\u003c\/dt\u003e\n\u003cdd\u003eDirect replacement\u003c\/dd\u003e\n\u003cdt\u003eOperating Temperature\u003c\/dt\u003e\n\u003cdd\u003e55°C (131°F)\u003c\/dd\u003e\n\u003cdt\u003eHousing Color\u003c\/dt\u003e\n\u003cdd\u003eSilver\/metallic\u003c\/dd\u003e\n\u003c\/dl\u003e\n\u003ch2\u003eWhat’s in the Box\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e1 x Thermostat (6D9-12411-00)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n\u003cli\u003eEnsure the engine is cool and disconnect the battery for safety.\u003c\/li\u003e\n\u003cli\u003eLocate the thermostat housing on the engine block or cylinder head.\u003c\/li\u003e\n\u003cli\u003ePlace a drain pan beneath the housing and carefully remove the cover bolts to release any remaining coolant.\u003c\/li\u003e\n\u003cli\u003eRemove the old thermostat. Note its orientation for correct placement of the new part.\u003c\/li\u003e\n\u003cli\u003eClean both the housing and cover surfaces thoroughly, removing all old gasket material.\u003c\/li\u003e\n\u003cli\u003eInstall the new thermostat in the correct orientation. A new gasket is highly recommended (not included).\u003c\/li\u003e\n\u003cli\u003eRe-install the housing cover and tighten the bolts to the manufacturer's recommended torque specification.\u003c\/li\u003e\n\u003cli\u003eRefill the cooling system with the appropriate coolant.\u003c\/li\u003e\n\u003cli\u003eReconnect the battery, start the engine, and carefully check for any leaks around the housing as the engine warms up.\u003c\/li\u003e\n\u003c\/ol\u003e\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n\u003csummary\u003eHow do I know if my thermostat has failed?\u003c\/summary\u003e\n\u003cp\u003eCommon signs include the engine overheating, especially at idle or low speeds, or the engine failing to reach its normal operating temperature. An inconsistent temperature gauge reading can also indicate a faulty thermostat.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eIs a new gasket required for installation?\u003c\/summary\u003e\n\u003cp\u003eYes, it is highly recommended to replace the thermostat housing gasket (not included) whenever replacing the thermostat to ensure a proper seal and prevent coolant leaks.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eAt what temperature does this thermostat open?\u003c\/summary\u003e\n\u003cp\u003eThis thermostat is calibrated to begin opening at 55°C (131°F) to allow coolant to circulate through the engine.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eWhat happens if I use the wrong temperature thermostat?\u003c\/summary\u003e\n\u003cp\u003eUsing a thermostat with a temperature rating that is too high can cause engine overheating. A rating that is too low will prevent the engine from reaching its optimal operating temperature, leading to reduced fuel efficiency, increased engine wear, and carbon buildup.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eOEM vs. Aftermarket?\u003c\/summary\u003e\n\u003cp\u003eThis listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eShipping speed \u0026amp; cost\u003c\/summary\u003e\n\u003cp\u003eWe ship worldwide quickly—typical transit 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 \u0026amp; returns\u003c\/summary\u003e\n\u003cp\u003eCovered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused \u0026amp; in original condition). See our policy page or reach out for instructions.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003ch2\u003eSafety \u0026amp; Important Info\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eVerify images\/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.\u003c\/li\u003e\n\u003cli\u003eThis is an aftermarket replacement, not an OEM component.\u003c\/li\u003e\n\u003cli\u003eProfessional installation is recommended for safety and performance.\u003c\/li\u003e\n\u003c\/ul\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 parts engineered to OEM-level tolerances and tested for 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 QC.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/section\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":50723984081211,"sku":"21TH014","price":50.5,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/Thermostat_for_Yamaha_4-Stroke_80-100HP_6D9-12411-00_-_JLM_MARINE-8290910.jpg?v=1763039392","url":"https:\/\/seasierra.com\/products\/thermostat-fits-yamaha-4-stroke-80-100hp-replaces-yamaha-6d9-12411-00-sierra-18-3639","provider":"SeaSierra","version":"1.0","type":"link"}