{"product_id":"sierra-18-3420-water-pump-base-for-mercruiser-alpha-one-mr-sterndrives-1985-1990-replaces-mercury-46-44292a3","title":"Sierra Water Pump Base 18-3420 for MerCruiser MR \u0026 Alpha One Drives (1985-1990), Replaces Mercury Marine 46-44292A3","description":"\u003cp\u003eThe Sierra 18-3420 Water Pump Base is an aluminum housing component for the raw water pump on MerCruiser MR and Alpha One stern drives (1985-1990). The water pump base serves as the mounting structure for the pump impeller assembly, directing raw water into the cooling circuit that keeps the engine and drive running at safe operating temperatures. Because it sits directly in the raw water flow path, the base is subject to corrosion and wear over time, and a compromised base can lead to reduced water flow, overheating, or impeller seal leaks -- making this a common maintenance and repair item for boaters servicing their MerCruiser cooling system.\u003c\/p\u003e\u003cp\u003eThis water pump base is built from aluminum for durability in a marine raw-water environment and is engineered as a fit-for-fit equivalent to Mercury Marine 46-44292A3. It is intended for MR and Alpha One drive owners performing a water pump rebuild or replacing a cracked, corroded, or worn original base as part of routine cooling system maintenance.\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 18-3420\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Aluminum\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 0.22 pounds\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFitment:\u003c\/strong\u003e MerCruiser MR \u0026amp; Alpha One drives (1985-1990)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUPC:\u003c\/strong\u003e 030999315922\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eMerCruiser MR \u0026amp; Alpha One drives (1985-1990)\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eReplaces (OEM)\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eMercury Marine 46-44292A3\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eWhat does the Sierra 18-3420 water pump base fit?\u003c\/strong\u003e The Sierra 18-3420 is designed for MerCruiser MR and Alpha One stern drives from 1985 to 1990.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the Sierra 18-3420 the same as Mercury Marine 46-44292A3?\u003c\/strong\u003e Yes, the 18-3420 is a direct equivalent to Mercury Marine part number 46-44292A3 and is built to match its fit and function.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat material is the water pump base made from?\u003c\/strong\u003e This water pump base, Sierra 18-3420, is made from aluminum.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much does the 18-3420 water pump base weigh?\u003c\/strong\u003e The Sierra 18-3420 water pump base weighs 0.22 pounds.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat role does the water pump base play in the cooling system?\u003c\/strong\u003e It is the housing that mounts the water pump impeller assembly on MerCruiser MR and Alpha One drives, directing raw water into the engine cooling circuit.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhen should I replace my water pump base?\u003c\/strong\u003e A cracked, corroded, or worn water pump base like the Sierra 18-3420 should be replaced if it is causing reduced water flow, leaks, or overheating in the raw water cooling system.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs this a genuine Mercury Marine part or an aftermarket part?\u003c\/strong\u003e The Sierra 18-3420 is an aftermarket water pump base manufactured by Sierra as an equivalent to Mercury Marine 46-44292A3, not an original Mercury Marine branded part.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes the 18-3420 come with the impeller included?\u003c\/strong\u003e No, the Sierra 18-3420 is the water pump base housing only; it does not include the impeller.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill the 18-3420 fit later MerCruiser Alpha One Generation II drives?\u003c\/strong\u003e The Sierra 18-3420 is specified for MR and Alpha One drives from 1985 to 1990; it is not listed for Alpha One Generation II applications.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat color or finish does the water pump base have?\u003c\/strong\u003e The Sierra 18-3420 water pump base has a natural aluminum finish.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs Sierra 18-3420 covered by a warranty?\u003c\/strong\u003e Yes, the Sierra 18-3420 water pump base is covered under Sierra's standard limited warranty against manufacturing defects.\u003c\/p\u003e","brand":"Sierra","offers":[{"title":"Default Title","offer_id":48988148400347,"sku":"SIE-18-3420","price":30.12,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0839\/7586\/4539\/files\/SIE-18-3420_lg__02303.1558126021.500.750.jpg?v=1785188108","url":"https:\/\/www.goodvibesmarina.com\/products\/sierra-18-3420-water-pump-base-for-mercruiser-alpha-one-mr-sterndrives-1985-1990-replaces-mercury-46-44292a3","provider":"Good Vibes Marina","version":"1.0","type":"link"}