{"product_id":"18-3642-outboard-thermostat-for-mercury-mariner-40hp-3cyl-jlm-marine","title":"18-3642 Outboard Thermostat for Mercury Mariner 40HP 3Cyl | JLM Marine","description":"\u003ch2\u003e18-3642 Outboard Thermostat for Mercury Mariner 40HP 3Cyl\u003c\/h2\u003e\n\n\u003cp\u003eThis thermostat is engineered to maintain optimal engine operating temperatures for Mercury Mariner 40HP 3-cylinder outboard motors (serial number 1C049739 and up). Designed as a direct replacement for multiple OEM part numbers, this component ensures reliable cooling system performance and prevents overheating damage.\u003c\/p\u003e\n\n\u003cp\u003eThis aftermarket thermostat replaces OEM numbers \u003cstrong\u003e825212\u003c\/strong\u003e, \u003cstrong\u003e825212 A1\u003c\/strong\u003e, \u003cstrong\u003e825212001\u003c\/strong\u003e, \u003cstrong\u003e855676003\u003c\/strong\u003e, \u003cstrong\u003e825212T02\u003c\/strong\u003e, and \u003cstrong\u003e855676A1\u003c\/strong\u003e, providing broad compatibility across Mercury Mariner outboard applications.\u003c\/p\u003e\n\n\u003cul\u003e\n\u003cli\u003eComplete installation kit with thermostat and rubber seal ring\u003c\/li\u003e\n\u003cli\u003eFits Mercury Mariner 40HP 3-cylinder outboards from serial 1C049739 onward\u003c\/li\u003e\n\u003cli\u003eDirect replacement for multiple OEM part numbers\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003ePart Number Cross-Reference\u003c\/h2\u003e\n\n\u003cp\u003eUse this table to confirm equivalent part numbers across OEM and aftermarket brands.\u003c\/p\u003e\n\n\u003ctable border=\"1\" cellpadding=\"8\" cellspacing=\"0\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eBrand\u003c\/th\u003e\n\u003cth\u003ePart Number\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eOEM\u003c\/td\u003e\n\u003ctd\u003e18-3642\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e825212\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e825212 A1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e825212001\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e855676003\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e825212T02\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e855676A1\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003eCompatible Engine Models\u003c\/h2\u003e\n\n\u003cp\u003eConfirm your engine model\/year in the table below. For Mercury owners, here's a guide to help you identify your engine's serial\/model: \u003ca href=\"https:\/\/jlmmarine.com\/blogs\/serial-number-guide\/mercury-outboard-serial-number-guide\" rel=\"nofollow noopener\" target=\"_blank\"\u003eMercury Serial Number Guide\u003c\/a\u003e. You can also review exploded diagrams to verify part numbers: \u003ca href=\"https:\/\/jlmmarine.com\/blogs\/diagrams\/mercury-parts-catalog\" rel=\"nofollow noopener\" target=\"_blank\"\u003eMercury Parts Diagrams \u0026amp; Catalog\u003c\/a\u003e.\u003c\/p\u003e\n\n\u003ctable border=\"1\" cellpadding=\"8\" cellspacing=\"0\"\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\u003eNotes\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003ctd\u003e40HP (3Cyl)\u003c\/td\u003e\n\u003ctd\u003e40HP\u003c\/td\u003e\n\u003ctd\u003eSerial 1C049739 \u0026amp; Up\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003eTechnical Specifications\u003c\/h2\u003e\n\n\u003ctable border=\"1\" cellpadding=\"8\" cellspacing=\"0\"\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eSpecification\u003c\/th\u003e\n\u003cth\u003eValue\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eOEM Number\u003c\/td\u003e\n\u003ctd\u003e18-3642\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eCompatible Brand\u003c\/td\u003e\n\u003ctd\u003eMercury Mariner\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eEngine Configuration\u003c\/td\u003e\n\u003ctd\u003e3-Cylinder\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eHorsepower\u003c\/td\u003e\n\u003ctd\u003e40HP\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\n\u003ch2\u003ePackage Contents\u003c\/h2\u003e\n\n\u003cul\u003e\n\u003cli\u003e\u003cspan style=\"color:red;\"\u003e1 × Thermostat\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan style=\"color:red;\"\u003e1 × Ring Rubber Seal\u003c\/span\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eInstallation Guide\u003c\/h2\u003e\n\n\u003col\u003e\n\u003cli\u003eDisconnect the battery and allow the engine to cool completely before beginning work.\u003c\/li\u003e\n\u003cli\u003eDrain the cooling system by removing the lower drain plug and allowing coolant to empty into a container.\u003c\/li\u003e\n\u003cli\u003eLocate the thermostat housing on the cylinder head and remove the retaining bolts using the appropriate socket.\u003c\/li\u003e\n\u003cli\u003eCarefully remove the old thermostat housing cover and inspect for corrosion or damage.\u003c\/li\u003e\n\u003cli\u003eRemove the old thermostat and rubber seal ring, cleaning all mating surfaces thoroughly with a gasket scraper.\u003c\/li\u003e\n\u003cli\u003eInstall the new rubber seal ring into the groove on the thermostat or housing (follow OEM positioning).\u003c\/li\u003e\n\u003cli\u003ePosition the new thermostat into the housing with the correct orientation (spring side typically faces down\/inward).\u003c\/li\u003e\n\u003cli\u003eReinstall the thermostat housing cover and tighten bolts to manufacturer specifications in a cross-pattern.\u003c\/li\u003e\n\u003cli\u003eReinstall the lower drain plug and refill the cooling system with fresh coolant to the proper level.\u003c\/li\u003e\n\u003cli\u003eReconnect the battery and start the engine, checking for leaks around the thermostat housing.\u003c\/li\u003e\n\u003cli\u003eAllow the engine to reach operating temperature and verify proper cooling system function.\u003c\/li\u003e\n\u003cli\u003eRecheck coolant level after initial run and top off if necessary.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: How do I confirm this thermostat fits my Mercury Mariner outboard?\u003c\/strong\u003e\u003cbr\u003e\nA: Verify that your engine is a 40HP 3-cylinder model with serial number 1C049739 or higher. Cross-reference your current thermostat part number with the OEM numbers listed (825212, 825212 A1, 825212001, 855676003, 825212T02, or 855676A1). You can also check Mercury's parts diagrams using your serial number to confirm compatibility.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: How often should I replace the thermostat on my outboard?\u003c\/strong\u003e\u003cbr\u003e\nA: Replace the thermostat if you experience overheating, inconsistent operating temperatures, or poor engine performance. As preventive maintenance, inspect the thermostat annually and replace every 3–5 years or per your engine manufacturer's service schedule, especially in saltwater environments.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: What are the signs that my thermostat is failing?\u003c\/strong\u003e\u003cbr\u003e\nA: Common symptoms include engine overheating, running too cool (poor fuel efficiency), erratic temperature gauge readings, or coolant leaks around the thermostat housing. If the engine takes longer than normal to warm up or frequently triggers overheat alarms, the thermostat may be stuck open or closed.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: Should I replace the rubber seal ring every time I replace the thermostat?\u003c\/strong\u003e\u003cbr\u003e\nA: Yes, always replace the rubber seal ring when installing a new thermostat to ensure a proper seal and prevent coolant leaks. This package includes a new seal ring for complete installation.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: Is this an OEM thermostat or an aftermarket replacement?\u003c\/strong\u003e\u003cbr\u003e\nA: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: How fast do you ship and how much does it cost?\u003c\/strong\u003e\u003cbr\u003e\nA: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eQ: What is your warranty and return policy?\u003c\/strong\u003e\u003cbr\u003e\nA: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused \u0026amp; in original condition); please see our policy page or reach out for instructions.\u003c\/p\u003e\n\n\u003ch2\u003eImportant Notes\u003c\/h2\u003e\n\n\u003cul\u003e\n\u003cli\u003eVerify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.\u003c\/li\u003e\n\u003cli\u003eThis product is an aftermarket replacement part and is not an OEM component.\u003c\/li\u003e\n\u003cli\u003eProfessional installation is recommended to ensure safety and optimal performance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eWhy Choose JLM MARINE?\u003c\/h2\u003e\n\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eQuality Assured:\u003c\/strong\u003e As a trusted manufacturer for over 20 years, we supply top marine brands globally.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFast Global Shipping:\u003c\/strong\u003e Free delivery worldwide in 5–15 days.\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eDirect from Manufacturer:\u003c\/strong\u003e Competitive pricing without compromising quality.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"JLM Marine","offers":[{"title":"Default Title","offer_id":51981006111033,"sku":"23TH641","price":24.5,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0885\/0433\/6697\/files\/12_1c9b9ed4-2700-48e1-a379-cfb191afd1d8.jpg?v=1772414482","url":"https:\/\/jlmmarine.com\/es\/products\/18-3642-outboard-thermostat-for-mercury-mariner-40hp-3cyl-jlm-marine","provider":"JLM Marine Boat Parts Limited","version":"1.0","type":"link"}