{"product_id":"marine-thermostat-for-johnson-evinrude-omc-brp-outboards-replaces-oem-433379-fits-6-55-hp-1990-1994-sierra-18-3643","title":"Sierra Thermostat 18-3643 for Johnson\/Evinrude 6 HP and 8 HP 1990 Outboards","description":"\u003cp\u003eThe Sierra 18-3643 is a thermostat built for the cooling system of Johnson\/Evinrude (OMC\/BRP) outboard motors. It is the correct thermostat for the 1990 model year 6 HP and 8 HP outboard engines in this engine family, where it regulates coolant flow through the powerhead to keep operating temperature within the engine's designed range. Maintaining the correct thermostat opening temperature protects the engine from running too cold (which reduces efficiency and promotes internal corrosion and carbon buildup) or too hot (which risks overheating damage), so a worn, stuck, or corroded thermostat is a common cause of erratic temperature gauge readings and cooling problems on these outboards.\u003c\/p\u003e\u003cp\u003eAs a direct-fit replacement part, the Sierra 18-3643 is sized and calibrated to install in place of the original thermostat used on the applicable Johnson\/Evinrude 6 HP and 8 HP 1990 powerheads, restoring proper coolant regulation without modification to the cooling system. It is a compact, lightweight component at 0.11 pounds, intended to be swapped in during routine cooling system maintenance or when troubleshooting overheating or overcooling symptoms.\u003c\/p\u003e\u003ch3\u003eSpecifications\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Sierra\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer Part Number:\u003c\/strong\u003e 18-3643\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eProduct Type:\u003c\/strong\u003e Thermostat\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCategory:\u003c\/strong\u003e Evinrude Outboard Thermostats and Gaskets\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFitment:\u003c\/strong\u003e Johnson\/Evinrude (OMC\/BRP) 6 HP, 1990\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFitment:\u003c\/strong\u003e Johnson\/Evinrude (OMC\/BRP) 8 HP, 1990\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 0.11 pounds\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUPC:\u003c\/strong\u003e 808282375508\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003eJohnson\/Evinrude (OMC\/BRP) 6 HP outboard, 1990\u003c\/li\u003e\n\u003cli\u003eJohnson\/Evinrude (OMC\/BRP) 8 HP outboard, 1990\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eWhat engines does the Sierra 18-3643 thermostat fit?\u003c\/strong\u003e The Sierra 18-3643 fits Johnson\/Evinrude (OMC\/BRP) 6 HP and 8 HP outboards from the 1990 model year.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much does this thermostat weigh?\u003c\/strong\u003e The Sierra 18-3643 thermostat weighs 0.11 pounds.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the part number I should order?\u003c\/strong\u003e The correct Sierra part number for this Johnson\/Evinrude 6 HP and 8 HP 1990 thermostat is 18-3643.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat does a thermostat do in an outboard cooling system?\u003c\/strong\u003e In the Johnson\/Evinrude 6 HP and 8 HP 1990 outboards this part fits, the thermostat regulates coolant flow through the powerhead so the engine reaches and holds its designed operating temperature.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat are signs the thermostat needs to be replaced?\u003c\/strong\u003e Erratic temperature gauge readings, the engine running too hot, or the engine running too cold can indicate the thermostat has failed and needs replacement, such as with the Sierra 18-3643 on applicable Johnson\/Evinrude 6 HP and 8 HP 1990 models.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the Sierra 18-3643 a genuine Sierra part?\u003c\/strong\u003e Yes, 18-3643 is a Sierra branded thermostat manufactured for Johnson\/Evinrude (OMC\/BRP) 6 HP and 8 HP 1990 outboard applications.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes this thermostat require any modification to install?\u003c\/strong\u003e No, the Sierra 18-3643 is sized to install as a direct replacement in the cooling system of the applicable Johnson\/Evinrude 6 HP and 8 HP 1990 outboard without modification.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the UPC for this product?\u003c\/strong\u003e The UPC for the Sierra 18-3643 thermostat is 808282375508.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill this thermostat work on other horsepower outboards outside 6 HP and 8 HP?\u003c\/strong\u003e The Sierra 18-3643 is designated for the 1990 model year Johnson\/Evinrude 6 HP and 8 HP outboards; other horsepower or model years are not confirmed fits for this part.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan a bad thermostat cause overheating on a Johnson\/Evinrude outboard?\u003c\/strong\u003e Yes, a stuck or corroded thermostat is a common cause of overheating on Johnson\/Evinrude 6 HP and 8 HP 1990 outboards, which is why replacing it with the Sierra 18-3643 is a routine cooling system fix.\u003c\/p\u003e","brand":"Sierra","offers":[{"title":"Default Title","offer_id":48988156362971,"sku":"SIE-18-3643","price":32.25,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0839\/7586\/4539\/files\/18-3643__14420.1722481412.500.750.jpg?v=1785188830","url":"https:\/\/www.goodvibesmarina.com\/products\/marine-thermostat-for-johnson-evinrude-omc-brp-outboards-replaces-oem-433379-fits-6-55-hp-1990-1994-sierra-18-3643","provider":"Good Vibes Marina","version":"1.0","type":"link"}