{"product_id":"mercruiser-thermostat-991551","title":"MerCruiser Thermostat – 991551","description":"\u003cp data-start=\"208\" data-end=\"408\"\u003eThe \u003cstrong data-start=\"212\" data-end=\"252\"\u003eMercury MerCruiser 991551 Thermostat\u003c\/strong\u003e is a genuine OEM \u003cstrong data-start=\"270\" data-end=\"297\"\u003e160°F (71°C) thermostat\u003c\/strong\u003e designed for GM-based MerCruiser marine engines equipped with \u003cstrong data-start=\"360\" data-end=\"407\"\u003eclosed cooling (freshwater cooling) systems\u003c\/strong\u003e.\u003c\/p\u003e\n\u003cp data-start=\"410\" data-end=\"705\"\u003eThis thermostat regulates coolant flow between the engine and heat exchanger, allowing the engine to reach and maintain optimal operating temperature. The \u003cstrong data-start=\"565\" data-end=\"586\"\u003e160°F calibration\u003c\/strong\u003e is critical for proper combustion efficiency, fuel management, and engine longevity on MPI and EFI MerCruiser engines.\u003c\/p\u003e\n\u003cp data-start=\"707\" data-end=\"973\"\u003eIt uses a \u003cstrong data-start=\"717\" data-end=\"748\"\u003ewax-element expansion valve\u003c\/strong\u003e, which opens progressively as temperature rises, ensuring stable coolant flow under varying engine loads. Built to Mercury Marine specifications, it delivers consistent opening characteristics, durability, and exact fitment.\u003c\/p\u003e\n\u003chr data-start=\"975\" data-end=\"978\"\u003e\n\u003ch2 data-start=\"980\" data-end=\"999\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"983\" data-end=\"999\"\u003eKey Features\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cul data-start=\"1000\" data-end=\"1315\"\u003e\n\u003cli data-start=\"1000\" data-end=\"1042\"\u003eGenuine Mercury \/ Quicksilver OEM part\u003c\/li\u003e\n\u003cli data-start=\"1043\" data-end=\"1082\"\u003e\n\u003cstrong data-start=\"1045\" data-end=\"1061\"\u003e160°F (71°C)\u003c\/strong\u003e temperature rating\u003c\/li\u003e\n\u003cli data-start=\"1083\" data-end=\"1131\"\u003eDesigned for \u003cstrong data-start=\"1098\" data-end=\"1129\"\u003eclosed cooling systems only\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli data-start=\"1132\" data-end=\"1181\"\u003eMaintains proper engine operating temperature\u003c\/li\u003e\n\u003cli data-start=\"1182\" data-end=\"1235\"\u003eImproves fuel efficiency and combustion stability\u003c\/li\u003e\n\u003cli data-start=\"1236\" data-end=\"1288\"\u003ePrevents overheating and cold-running conditions\u003c\/li\u003e\n\u003cli data-start=\"1289\" data-end=\"1315\"\u003eDirect OEM replacement\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"1317\" data-end=\"1320\"\u003e\n\u003ch2 data-start=\"1322\" data-end=\"1349\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"1325\" data-end=\"1349\"\u003eEngine Compatibility\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003ch3 data-start=\"1351\" data-end=\"1394\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"1355\" data-end=\"1394\"\u003eMerCruiser GM-Based Engines (1998+)\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h3\u003e\n\u003cp data-start=\"1395\" data-end=\"1412\"\u003eCommonly used on:\u003c\/p\u003e\n\u003cul data-start=\"1413\" data-end=\"1562\"\u003e\n\u003cli data-start=\"1413\" data-end=\"1438\"\u003e\u003cstrong data-start=\"1415\" data-end=\"1436\"\u003e4.3L V6 (262 CID)\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli data-start=\"1439\" data-end=\"1464\"\u003e\u003cstrong data-start=\"1441\" data-end=\"1462\"\u003e5.0L V8 (305 CID)\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli data-start=\"1465\" data-end=\"1490\"\u003e\u003cstrong data-start=\"1467\" data-end=\"1488\"\u003e5.7L V8 (350 CID)\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli data-start=\"1491\" data-end=\"1522\"\u003e\u003cstrong data-start=\"1493\" data-end=\"1520\"\u003e6.2L V8 (MPI \/ Horizon)\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli data-start=\"1523\" data-end=\"1562\"\u003e\u003cstrong data-start=\"1525\" data-end=\"1560\"\u003e7.4L \/ 8.2L (454 \/ 502 MAG MPI)\u003c\/strong\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp data-start=\"1564\" data-end=\"1585\"\u003e➡️ Fits engines with:\u003c\/p\u003e\n\u003cul data-start=\"1586\" data-end=\"1754\"\u003e\n\u003cli data-start=\"1586\" data-end=\"1616\"\u003e\u003cstrong data-start=\"1588\" data-end=\"1614\"\u003eMPI \/ EFI fuel systems\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli data-start=\"1617\" data-end=\"1664\"\u003e\u003cstrong data-start=\"1619\" data-end=\"1662\"\u003eAlpha \u0026amp; Bravo sterndrive configurations\u003c\/strong\u003e\u003c\/li\u003e\n\u003cli data-start=\"1665\" data-end=\"1754\"\u003e\n\u003cstrong data-start=\"1667\" data-end=\"1714\"\u003eClosed cooling (freshwater cooling) systems\u003c\/strong\u003e \u003cspan class=\"\" data-state=\"closed\"\u003e\u003c\/span\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"1756\" data-end=\"1759\"\u003e\n\u003ch2 data-start=\"1761\" data-end=\"1791\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"1764\" data-end=\"1791\"\u003eImportant Fitment Notes\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cul data-start=\"1792\" data-end=\"1998\"\u003e\n\u003cli data-start=\"1792\" data-end=\"1843\"\u003e✔ Designed for \u003cstrong data-start=\"1809\" data-end=\"1841\"\u003eclosed cooling systems (FWC)\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli data-start=\"1844\" data-end=\"1915\"\u003e❌ Not for raw water cooled engines requiring lower temp thermostats\u003c\/li\u003e\n\u003cli data-start=\"1916\" data-end=\"1998\"\u003e✔ Common on \u003cstrong data-start=\"1930\" data-end=\"1958\"\u003e1998+ MerCruiser engines\u003c\/strong\u003e \u003cspan class=\"\" data-state=\"closed\"\u003e\u003c\/span\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2000\" data-end=\"2003\"\u003e\n\u003ch2 data-start=\"2005\" data-end=\"2026\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2008\" data-end=\"2026\"\u003eSpecifications\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cul data-start=\"2027\" data-end=\"2211\"\u003e\n\u003cli data-start=\"2027\" data-end=\"2054\"\u003ePart Number: \u003cstrong data-start=\"2042\" data-end=\"2052\"\u003e991551\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli data-start=\"2055\" data-end=\"2095\"\u003eTemperature Rating: \u003cstrong data-start=\"2077\" data-end=\"2093\"\u003e160°F (71°C)\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli data-start=\"2096\" data-end=\"2123\"\u003eType: Engine thermostat\u003c\/li\u003e\n\u003cli data-start=\"2124\" data-end=\"2171\"\u003eOperation: Wax-element, spring-loaded valve\u003c\/li\u003e\n\u003cli data-start=\"2172\" data-end=\"2211\"\u003eApplication: Closed cooling systems\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2213\" data-end=\"2216\"\u003e\n\u003ch2 data-start=\"2218\" data-end=\"2240\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2221\" data-end=\"2240\"\u003eWhat’s Included\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cul data-start=\"2241\" data-end=\"2295\"\u003e\n\u003cli data-start=\"2241\" data-end=\"2295\"\u003eThermostat (gasket sold separately unless specified)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2297\" data-end=\"2300\"\u003e\n\u003ch2 data-start=\"2302\" data-end=\"2341\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2305\" data-end=\"2341\"\u003eWhen This Part Needs Replacement\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cul data-start=\"2342\" data-end=\"2489\"\u003e\n\u003cli data-start=\"2342\" data-end=\"2384\"\u003eEngine not reaching proper temperature\u003c\/li\u003e\n\u003cli data-start=\"2385\" data-end=\"2418\"\u003eEngine overheating under load\u003c\/li\u003e\n\u003cli data-start=\"2419\" data-end=\"2447\"\u003eTemperature fluctuations\u003c\/li\u003e\n\u003cli data-start=\"2448\" data-end=\"2489\"\u003ePoor fuel efficiency or rough running\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2491\" data-end=\"2494\"\u003e\n\u003ch2 data-start=\"2496\" data-end=\"2521\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2499\" data-end=\"2521\"\u003eInstallation Notes\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cul data-start=\"2522\" data-end=\"2711\"\u003e\n\u003cli data-start=\"2522\" data-end=\"2581\"\u003eInstall with correct orientation (spring toward engine)\u003c\/li\u003e\n\u003cli data-start=\"2582\" data-end=\"2625\"\u003eReplace gasket\/seal during installation\u003c\/li\u003e\n\u003cli data-start=\"2626\" data-end=\"2664\"\u003eClean housing and sealing surfaces\u003c\/li\u003e\n\u003cli data-start=\"2665\" data-end=\"2711\"\u003eVerify operating temperature after install\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2713\" data-end=\"2716\"\u003e\n\u003ch2 data-start=\"2718\" data-end=\"2760\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2721\" data-end=\"2760\"\u003eAlternate \/ Superseded Part Numbers\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003ch3 data-start=\"2762\" data-end=\"2790\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2766\" data-end=\"2790\"\u003eOEM Cross References\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h3\u003e\n\u003cul data-start=\"2791\" data-end=\"2866\"\u003e\n\u003cli data-start=\"2791\" data-end=\"2827\"\u003eMercury \/ MerCruiser: \u003cstrong data-start=\"2815\" data-end=\"2825\"\u003e991551\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003cli data-start=\"2828\" data-end=\"2866\"\u003eQuicksilver equivalent: \u003cstrong data-start=\"2854\" data-end=\"2864\"\u003e991551\u003c\/strong\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003chr data-start=\"2868\" data-end=\"2871\"\u003e\n\u003ch2 data-start=\"2873\" data-end=\"2890\"\u003e\u003cspan role=\"text\"\u003e\u003cstrong data-start=\"2876\" data-end=\"2888\"\u003eShipping\u003c\/strong\u003e\u003c\/span\u003e\u003c\/h2\u003e\n\u003cp data-start=\"2891\" data-end=\"2958\"\u003eShipping: Ships same or next day for fast Canada wide shipping. ⚓\u003c\/p\u003e\n\u003chr data-start=\"2960\" data-end=\"2963\"\u003e\n\u003ch3 data-start=\"2965\" data-end=\"2992\"\u003e💡 Parts Desk Insight\u003c\/h3\u003e\n\u003cp data-start=\"2993\" data-end=\"3133\"\u003eThis is the \u003cstrong data-start=\"3005\" data-end=\"3053\"\u003estandard 160° thermostat for MPI MerCruisers\u003c\/strong\u003e—if your engine runs cold or throws fuel trim issues, this is usually the fix 👍\u003c\/p\u003e","brand":"MERC","offers":[{"title":"Default Title","offer_id":43563929272356,"sku":"991551","price":62.69,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0743\/5799\/7604\/files\/79f1e899-8191-4a05-b33f-1da00c626d0e.png?v=1774388082","url":"https:\/\/marisolmarine.com\/products\/mercruiser-thermostat-991551","provider":"Marisol Marine Company","version":"1.0","type":"link"}