{"product_id":"mercury-thermostat-fits-1998-newer-gm-vaeu-6-vaeu-8-engines-with-closed-cooling-991551","title":"Mercury – Thermostat | Cooling System | Factory Marine Finish | 991551","description":"\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eMercury – Thermostat | Cooling System | Factory Marine Finish | 991551\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eOverview\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003eThere’s a certain comfort in watching your engine settle into that perfect operating temperature—steady, calm, and exactly where it should be. It’s the feeling you get when you’ve been on the water long enough to know when something is right, and when something isn’t. A good thermostat doesn’t shout for attention; it simply keeps the heart of your boat running smooth and predictable. That quiet reliability is why so many boaters trust Mercury Marine parts like the 991551 thermostat.\u003c\/span\u003e\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eKey Features\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cspan data-preserver-spaces=\"true\"\u003eM\u003c\/span\u003e\u003cspan data-preserver-spaces=\"true\"\u003eaintains precise 160-degree Fahrenheit engine operating temperature\u003c\/span\u003e\n\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eDesigned for MerCruiser V6 and V8 General Motors–based marine engines\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eBuilt with durable marine-grade materials for long-term temperature stability\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eFactory-engineered to promote efficient coolant flow and consistent heat regulation\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eDirect replacement designed for easy installation using common tools\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan data-preserver-spaces=\"true\"\u003eS\u003c\/span\u003e\u003cspan data-preserver-spaces=\"true\"\u003eupports closed-cooling systems requiring a 160-degree thermostat\u003c\/span\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eEngine \u0026amp; Boat Compatibility\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eFits 1998 and newer MerCruiser marinized V6 and V8 engines\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eCompatible with closed-cooling systems built on General Motors engine platforms\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eIdeal for cruisers, sport boats, runabouts, bowriders, and family recreation boats\u003c\/span\u003e\u003c\/li\u003e\n\u003cli\u003e\u003cspan data-preserver-spaces=\"true\"\u003eSuitable for engines that depend on steady operating temperatures for fuel efficiency and long-term durability\u003c\/span\u003e\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003ePerformance \u0026amp; Practical Benefits\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003eA thermostat might be small, but you’ll feel its absence immediately when it’s not doing its job. With the Mercury Marine part 991551 installed, your engine reaches its ideal temperature quickly and stays there. That means smoother idling, cleaner combustion, and more predictable power when you lean into the throttle. Everything feels a bit steadier—no wandering temperatures, no unnecessary strain, no guessing whether your cooling system is keeping up.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003eBecause this thermostat is built specifically for marine use, it handles the constant changes in workload and water temperature that boats experience. The fit is tight and secure, sitting exactly where it should without fighting alignment or installation. Once it’s in place, the engine responds with a more confident rhythm. Your fuel system, ignition timing, and cooling passages all work together more efficiently when the temperature remains stable, and this thermostat makes that happen every time you head out.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003eFor boaters who spend long days cruising or towing, that stability translates to better performance and longer engine life. And when you’re miles from the ramp, that peace of mind is worth more than any spec sheet can say.\u003c\/span\u003e\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eWhy Buy OEM\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003eThere’s a big difference between a thermostat that simply fits and one that’s engineered for your exact engine. With an OEM Mercury Marine part, you’re getting the proper temperature rating, the correct response time, and the durability expected from factory-grade components. Aftermarket parts often fall short in consistency, which can lead to uneven heating, poor performance, or premature failure.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003eThe Mercury Marine part number 991551 is designed to match your engine’s cooling system perfectly. It’s reliable, cost-effective over the long haul, and delivers the kind of performance you only get from original equipment. When you want your engine to run right the first time—and every time—OEM is the way to go.\u003c\/span\u003e\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eFAQ\u003c\/span\u003e\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eQ1: Which engines does the 991551 thermostat fit?\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003e It fits 1998 and newer MerCruiser marinized V6 and V8 engines with closed-cooling systems requiring a 160-degree thermostat.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eQ2:\u003c\/span\u003e\u003cspan data-preserver-spaces=\"true\"\u003e How is this different from aftermarket versions?\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003e This thermostat is engineered to Mercury’s strict specifications, offering precise temperature control and long-term reliability.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eQ3: How do I confirm it’s the correct replacement?\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003e Check your engine’s parts listing or owner’s manual for the exact part number required by your cooling system.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eQ\u003c\/span\u003e\u003cspan data-preserver-spaces=\"true\"\u003e4: Can it be used in saltwater and freshwater environments?\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003e Yes, it’s built for both and designed to withstand harsh marine conditions.\u003c\/span\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cspan data-preserver-spaces=\"true\"\u003eQ5: Is installation straightforward?\u003c\/span\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003e\u003cspan data-preserver-spaces=\"true\"\u003e Most owners can replace it using basic tools by following the procedure outlined in their service manual.\u003c\/span\u003e\u003c\/p\u003e","brand":"Mercury","offers":[{"title":"Default Title","offer_id":46933434663203,"sku":"991551","price":35.11,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0783\/7410\/9475\/files\/991551_main.jpg?v=1760631534","url":"https:\/\/partsvu.com\/fr\/products\/mercury-thermostat-fits-1998-newer-gm-vaeu-6-vaeu-8-engines-with-closed-cooling-991551","provider":"PartsVu","version":"1.0","type":"link"}