{"product_id":"sierra-18-3667-marine-thermostat","title":"Sierra 18-3667 Marine Thermostat","description":"\u003cp\u003e\u003cimg src=\"https:\/\/cdn.shopify.com\/s\/files\/1\/0056\/9429\/2079\/files\/sierra-marine-engine-and-drive-parts-vector-logo.png?v=1777654573\" alt=\"\"\u003e\u003c\/p\u003e\n\u003cdiv class=\"\" data-turn-id-container=\"request-69ea37f2-9634-83ea-95ed-3658eca80b3e-9\" data-is-intersecting=\"true\"\u003e\n\u003cdiv class=\"relative w-full overflow-visible\"\u003e\n\u003csection class=\"text-token-text-primary w-full focus:outline-none [--shadow-height:45px] has-data-writing-block:pointer-events-none has-data-writing-block:-mt-(--shadow-height) has-data-writing-block:pt-(--shadow-height) [\u0026amp;:has([data-writing-block])\u0026gt;*]:pointer-events-auto R6Vx5W_threadScrollVars scroll-mb-[calc(var(--scroll-root-safe-area-inset-bottom,0px)+var(--thread-response-height))] scroll-mt-[calc(var(--header-height)+min(200px,max(70px,20svh)))]\" dir=\"auto\" data-turn-id=\"request-69ea37f2-9634-83ea-95ed-3658eca80b3e-9\" data-turn-id-container=\"request-69ea37f2-9634-83ea-95ed-3658eca80b3e-9\" data-testid=\"conversation-turn-204\" data-scroll-anchor=\"false\" data-turn=\"assistant\"\u003e\n\u003cdiv class=\"text-base my-auto mx-auto pb-10 [--thread-content-margin:var(--thread-content-margin-xs,calc(var(--spacing)*4))] @w-sm\/main:[--thread-content-margin:var(--thread-content-margin-sm,calc(var(--spacing)*6))] @w-lg\/main:[--thread-content-margin:var(--thread-content-margin-lg,calc(var(--spacing)*16))] px-(--thread-content-margin)\"\u003e\n\u003cdiv class=\"[--thread-content-max-width:40rem] @w-lg\/main:[--thread-content-max-width:48rem] mx-auto max-w-(--thread-content-max-width) flex-1 group\/turn-messages focus-visible:outline-hidden relative flex w-full min-w-0 flex-col agent-turn\"\u003e\n\u003cdiv class=\"flex max-w-full flex-col gap-4 grow\"\u003e\n\u003cdiv data-message-author-role=\"assistant\" data-message-id=\"d1533cb4-5c20-43a2-a2cc-ee882e1f096f\" dir=\"auto\" data-message-model-slug=\"gpt-5-5\" class=\"min-h-8 text-message relative flex w-full flex-col items-end gap-2 text-start break-words whitespace-normal outline-none keyboard-focused:focus-ring [.text-message+\u0026amp;]:mt-1\" data-turn-start-message=\"true\" tabindex=\"0\"\u003e\n\u003cdiv class=\"flex w-full flex-col gap-1 empty:hidden\"\u003e\n\u003cdiv class=\"markdown prose dark:prose-invert wrap-break-word w-full light markdown-new-styling\"\u003e\n\u003ch2 data-section-id=\"dwglzw\" data-start=\"0\" data-end=\"37\"\u003eSierra 18-3667 Marine Thermostat\u003c\/h2\u003e\n\u003cp data-start=\"40\" data-end=\"365\"\u003eMaintain proper engine temperature and dependable cooling system performance with the Sierra 18-3667 Thermostat. Designed as a high-quality replacement for select marine engines, this thermostat regulates coolant flow to help your engine reach and maintain optimal operating temperature under varying conditions on the water.\u003c\/p\u003e\n\u003cp data-start=\"367\" data-end=\"748\"\u003eThe thermostat is a critical component in any marine cooling system. It controls when coolant circulates through the engine, helping improve engine efficiency while preventing overheating during extended operation. A worn or sticking thermostat can cause inconsistent temperature readings, poor fuel economy, hard starting, or overheating issues that may lead to expensive repairs.\u003c\/p\u003e\n\u003cp data-start=\"750\" data-end=\"1078\"\u003eBuilt using durable marine-grade materials, the Sierra 18-3667 is engineered to meet or exceed OEM specifications for reliable performance and long service life in harsh marine environments. Designed as a direct replacement, it provides dependable fitment and straightforward installation for routine cooling system maintenance.\u003c\/p\u003e\n\u003chr data-start=\"1080\" data-end=\"1083\"\u003e\n\u003ch3 data-section-id=\"lmqikf\" data-start=\"1085\" data-end=\"1113\"\u003eCommon Engine Fitments\u003c\/h3\u003e\n\u003cp data-start=\"1114\" data-end=\"1215\"\u003eThe Sierra 18-3667 thermostat is commonly used on a variety of marine engine applications, including:\u003c\/p\u003e\n\u003cul data-start=\"1217\" data-end=\"1411\"\u003e\n\u003cli data-section-id=\"9eyza6\" data-start=\"1217\" data-end=\"1239\"\u003eMerCruiser 4.3L V6\u003c\/li\u003e\n\u003cli data-section-id=\"jlix76\" data-start=\"1240\" data-end=\"1262\"\u003eMerCruiser 5.0L V8\u003c\/li\u003e\n\u003cli data-section-id=\"xlwk5x\" data-start=\"1263\" data-end=\"1285\"\u003eMerCruiser 5.7L V8\u003c\/li\u003e\n\u003cli data-section-id=\"t37bu1\" data-start=\"1286\" data-end=\"1308\"\u003ePCM Excalibur 5.7L\u003c\/li\u003e\n\u003cli data-section-id=\"1rglafd\" data-start=\"1309\" data-end=\"1330\"\u003ePCM GT40 Ford 351\u003c\/li\u003e\n\u003cli data-section-id=\"1juraxn\" data-start=\"1331\" data-end=\"1370\"\u003eVolvo Penta 5.0Gi and 5.7Gi engines\u003c\/li\u003e\n\u003cli data-section-id=\"1dc4lw1\" data-start=\"1371\" data-end=\"1411\"\u003eOMC Cobra 5.0L and 5.7L applications\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp data-start=\"1413\" data-end=\"1451\"\u003eThese engines are frequently found in:\u003c\/p\u003e\n\u003cul data-start=\"1453\" data-end=\"1676\"\u003e\n\u003cli data-section-id=\"wmzc5h\" data-start=\"1453\" data-end=\"1489\"\u003eSea Ray sport boats and cruisers\u003c\/li\u003e\n\u003cli data-section-id=\"n4pz9n\" data-start=\"1490\" data-end=\"1514\"\u003eChaparral SSi models\u003c\/li\u003e\n\u003cli data-section-id=\"1mt7yc7\" data-start=\"1515\" data-end=\"1544\"\u003eFour Winns Horizon series\u003c\/li\u003e\n\u003cli data-section-id=\"zx4fe4\" data-start=\"1545\" data-end=\"1585\"\u003eMalibu Wakesetter and Response boats\u003c\/li\u003e\n\u003cli data-section-id=\"1x7qtpx\" data-start=\"1586\" data-end=\"1639\"\u003eCorrect Craft Ski Nautique and Super Air Nautique\u003c\/li\u003e\n\u003cli data-section-id=\"1co8t6t\" data-start=\"1640\" data-end=\"1676\"\u003eSupra Launch and Sunsport models\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp data-start=\"1678\" data-end=\"1844\"\u003eFitment can vary depending on cooling system design and engine serial number, so confirming compatibility with part number \u003cstrong data-start=\"1801\" data-end=\"1812\"\u003e18-3667\u003c\/strong\u003e before ordering is recommended.\u003c\/p\u003e\n\u003chr data-start=\"1846\" data-end=\"1849\"\u003e\n\u003ch3 data-section-id=\"1iz91iu\" data-start=\"1851\" data-end=\"1867\"\u003eKey Features\u003c\/h3\u003e\n\u003cul data-start=\"1868\" data-end=\"2219\"\u003e\n\u003cli data-section-id=\"crnunj\" data-start=\"1868\" data-end=\"1909\"\u003eHigh-quality marine engine thermostat\u003c\/li\u003e\n\u003cli data-section-id=\"pcx6hy\" data-start=\"1910\" data-end=\"1964\"\u003eHelps maintain proper engine operating temperature\u003c\/li\u003e\n\u003cli data-section-id=\"1v7yn6n\" data-start=\"1965\" data-end=\"2031\"\u003eRestores dependable coolant circulation and cooling efficiency\u003c\/li\u003e\n\u003cli data-section-id=\"1i3xki4\" data-start=\"2032\" data-end=\"2102\"\u003eCompatible with MerCruiser, PCM, Volvo Penta, and OMC applications\u003c\/li\u003e\n\u003cli data-section-id=\"1vrjtg0\" data-start=\"2103\" data-end=\"2163\"\u003eMarine-grade construction for durability and reliability\u003c\/li\u003e\n\u003cli data-section-id=\"1g0fq3l\" data-start=\"2164\" data-end=\"2219\"\u003eDirect replacement for straightforward installation\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2221\" data-end=\"2224\"\u003e\n\u003ch3 data-section-id=\"j1di0l\" data-start=\"2226\" data-end=\"2264\"\u003eWhy Replace a Marine Thermostat?\u003c\/h3\u003e\n\u003cp data-start=\"2265\" data-end=\"2530\"\u003eOver time, thermostats can stick open or closed from repeated heat cycles and corrosion exposure. Replacing a failing thermostat helps maintain stable engine temperatures, improve cooling system performance, and reduce the risk of overheating-related engine damage.\u003c\/p\u003e\n\u003cp data-start=\"2532\" data-end=\"2712\" data-is-last-node=\"\" data-is-only-node=\"\"\u003eIf you’re servicing a compatible inboard or sterndrive marine engine, the Sierra 18-3667 thermostat delivers dependable cooling performance and OEM-style reliability you can trust.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"z-0 flex min-h-[46px] justify-start\"\u003e\u003cbr\u003e\u003c\/div\u003e\n\u003cdiv class=\"mt-3 w-full empty:hidden\"\u003e\n\u003cdiv class=\"text-center\"\u003e\u003cbr\u003e\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/section\u003e\n\u003cdiv class=\"contents\"\u003e\u003cbr\u003e\u003c\/div\u003e\n\u003c\/div\u003e\n\u003c\/div\u003e","brand":"Inboard Parts HQ","offers":[{"title":"Default Title","offer_id":48754003116289,"sku":"47-3667","price":23.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0056\/9429\/2079\/files\/Screenshot2026-05-09121723.png?v=1778343602","url":"https:\/\/inboardpartshq.com\/products\/sierra-18-3667-marine-thermostat","provider":"Inboard Parts HQ","version":"1.0","type":"link"}