{"product_id":"water-pump-impeller-service-kit-fits-yamaha-2-stroke-40-50-hp-replaces-6h4-w0078-00-18-3408-18-3429","title":"Water Pump Impeller Service Kit – Fits Yamaha 2-Stroke 40\/50 HP (Replaces 6H4-W0078-00, 18-3408, 18-3429)","description":"\u003csection\u003e\n\u003c!-- 🔧 Table Styles (include only once per page) --\u003e\n\u003cstyle\u003e\n  \/* Outer container allows horizontal scrolling (with iOS momentum) *\/\n  .ss-table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; }\n\n  \/* Base table styles *\/\n  table.ss-table { width:100%; border-collapse:collapse; min-width:640px; }\n  table.ss-table th, table.ss-table td {\n    padding:10px 12px; border:1px solid #e5e7eb; text-align:left; vertical-align:top;\n  }\n\n  \/* Key: prevent wrapping, word breaks, and vertical text in headers *\/\n  table.ss-table th {\n    white-space:nowrap;       \/* Do not wrap *\/\n    word-break:normal;        \/* Don’t break words *\/\n    letter-spacing:normal;    \/* Prevent theme styles from stretching letters *\/\n    font-weight:600;\n    background:#f8fafc;\n  }\n\n  \/* Small screen optimization *\/\n  @media (max-width:480px){\n    table.ss-table th, table.ss-table td { padding:8px 10px; font-size:14px; }\n  }\n\u003c\/style\u003e\n\n\u003ch2\u003eProduct Details\u003c\/h2\u003e\n\u003cp\u003eThis \u003cstrong\u003eWater Pump Impeller Service Kit\u003c\/strong\u003e is designed for Yamaha 2-stroke outboard motors, specifically fitting 40 HP models from 1995–2005 and 50 HP models (including the Pro Series P50) from 1998–2009. It provides all necessary components for a complete water pump overhaul to restore cooling performance.\u003c\/p\u003e\n\u003cp\u003eThis kit serves as a direct replacement for Yamaha OEM part numbers 6H4-W0078-00, 6H4-W0078-00-00, 6H4-W0078-01-00, and 6H4-W0078-A0-00, as well as Sierra aftermarket parts 18-3408 and 18-3429.\u003c\/p\u003e\n\u003cul\u003e\n\u003cli\u003eInstalls in the lower unit of the outboard motor.\u003c\/li\u003e\n\u003cli\u003eFeatures a durable neoprene impeller for reliable performance.\u003c\/li\u003e\n\u003cli\u003eEngineered as a direct OEM-compatible replacement part.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003ePart Number Matrix\u003c\/h2\u003e\n\u003cp\u003eUse this matrix to confirm equivalent references across OEM and aftermarket.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Part Number Cross-Reference\"\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\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00-00\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-01-00\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-A0-00\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eSierra\u003c\/td\u003e\n        \u003ctd\u003e18-3408\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eSierra\u003c\/td\u003e\n        \u003ctd\u003e18-3429\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eEngine \u0026amp; Model Compatibility\u003c\/h2\u003e\n\u003cp\u003eConfirm your engine model\/year in the table below.\u003c\/p\u003e\n\u003cp\u003eFor Yamaha owners, please verify your engine's model and production year against this list to ensure proper fitment of the water pump kit.\u003c\/p\u003e\n\u003cdiv class=\"ss-table-wrap\"\u003e\n  \u003ctable class=\"ss-table\" aria-label=\"Compatible Engine Models\"\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\u003eStroke\u003c\/th\u003e\n        \u003cth\u003eYears\u003c\/th\u003e\n        \u003cth\u003eOEM Part No.\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\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e40 HP\u003c\/td\u003e\n        \u003ctd\u003e40\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1995–2005\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003e50 HP\u003c\/td\u003e\n        \u003ctd\u003e50\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1998–2009\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n      \u003ctr\u003e\n        \u003ctd\u003eYamaha\u003c\/td\u003e\n        \u003ctd\u003eP50 (Pro Series)\u003c\/td\u003e\n        \u003ctd\u003e50\u003c\/td\u003e\n        \u003ctd\u003e2-Stroke\u003c\/td\u003e\n        \u003ctd\u003e1998–2009\u003c\/td\u003e\n        \u003ctd\u003e6H4-W0078-00\u003c\/td\u003e\n        \u003ctd\u003e\u003c\/td\u003e\n      \u003c\/tr\u003e\n    \u003c\/tbody\u003e\n  \u003c\/table\u003e\n\u003c\/div\u003e\n\n\u003ch2\u003eTechnical Specs\u003c\/h2\u003e\n\u003cdl\u003e\n  \u003cdt\u003eProduct Type\u003c\/dt\u003e\n\u003cdd\u003eWater Pump Impeller Service Kit\u003c\/dd\u003e\n  \u003cdt\u003eInstallation\u003c\/dt\u003e\n\u003cdd\u003eLower Unit\u003c\/dd\u003e\n  \u003cdt\u003eMaterial\u003c\/dt\u003e\n\u003cdd\u003eNeoprene (Impeller)\u003c\/dd\u003e\n  \u003cdt\u003eWeight\u003c\/dt\u003e\n\u003cdd\u003e0.25 kg (0.55 lb)\u003c\/dd\u003e\n  \u003cdt\u003eOther Technical Attributes\u003c\/dt\u003e\n\u003cdd\u003eOriginal Equipment Manufacturer (OEM) or OEM-compatible replacement\u003c\/dd\u003e\n\u003c\/dl\u003e\n\n\u003ch2\u003eWhat’s in the Box\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003e1 x Water Pump Impeller (6H4-44352-00)\u003c\/li\u003e\n\u003cli\u003e1 x Wear Plate\u003c\/li\u003e\n\u003cli\u003e1 x Insert Cup\u003c\/li\u003e\n\u003cli\u003e1 x Water Pump Gasket\u003c\/li\u003e\n\u003cli\u003e1 x Key\u003c\/li\u003e\n\u003cli\u003e1 x Water Seal\u003c\/li\u003e\n\u003cli\u003e1 x \"O\"-Ring\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eInstallation Notes\u003c\/h2\u003e\n\u003col\u003e\n\u003cli\u003eDisconnect the spark plug leads and shift the outboard into the neutral position.\u003c\/li\u003e\n\u003cli\u003eLocate and remove the bolts securing the lower unit (gearcase) to the upper casing.\u003c\/li\u003e\n\u003cli\u003eCarefully separate and lower the gearcase from the driveshaft housing. Be mindful of the shift shaft.\u003c\/li\u003e\n\u003cli\u003eUnbolt the water pump housing cover to access the impeller.\u003c\/li\u003e\n\u003cli\u003eRemove the old impeller, woodruff key, wear plate, and any gaskets or seals.\u003c\/li\u003e\n\u003cli\u003eClean the housing and mating surfaces meticulously, removing any old gasket material or corrosion.\u003c\/li\u003e\n\u003cli\u003eInstall the new wear plate and gasket. Place the new woodruff key on the driveshaft.\u003c\/li\u003e\n\u003cli\u003eAlign the keyway and slide the new impeller onto the driveshaft. Turn the shaft clockwise to help seat the vanes.\u003c\/li\u003e\n\u003cli\u003eInstall the new insert cup and gasket onto the housing, then secure the housing with its bolts.\u003c\/li\u003e\n\u003cli\u003eRe-attach the lower unit to the engine, ensuring the driveshaft, water tube, and shift shaft align correctly. Tighten bolts to the manufacturer's specified torque.\u003c\/li\u003e\n\u003c\/ol\u003e\n\n\u003ch2\u003eTroubleshooting \u0026amp; FAQ\u003c\/h2\u003e\n\u003cdetails\u003e\n\u003csummary\u003eHow do I know this kit fits my Yamaha outboard?\u003c\/summary\u003e\n\u003cp\u003eThis kit is specifically for Yamaha 2-Stroke 40 HP (1995–2005) and 50 HP (1998–2009) models. The most reliable way to confirm fit is to check your engine's model and year against our compatibility table. You can also match your existing part number to the cross-references listed in the Part Number Matrix.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eWhat are the signs of a failing water pump impeller?\u003c\/summary\u003e\n\u003cp\u003eCommon symptoms include the engine overheating at idle or low speeds, a weak or non-existent stream of water from the \"tell-tale\" outlet, or visible damage (cracked, brittle, or missing vanes) on the old impeller during inspection.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eHow often should this water pump kit be replaced?\u003c\/summary\u003e\n\u003cp\u003eAs a preventative maintenance item, it is generally recommended to replace the water pump impeller and service the pump every one to two years, or every 100-200 hours of operation, depending on usage conditions (e.g., saltwater vs. freshwater).\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eOEM vs. Aftermarket?\u003c\/summary\u003e\n\u003cp\u003eThis listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eShipping speed \u0026amp; cost?\u003c\/summary\u003e\n\u003cp\u003eWe ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.\u003c\/p\u003e\n\u003c\/details\u003e\n\u003cdetails\u003e\n\u003csummary\u003eWarranty \u0026amp; returns?\u003c\/summary\u003e\n\u003cp\u003eCovered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused \u0026amp; in original condition). See our policy page or reach out for instructions.\u003c\/p\u003e\n\u003c\/details\u003e\n\n\u003ch2\u003eSafety \u0026amp; Important Info\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003eVerify images\/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.\u003c\/li\u003e\n\u003cli\u003eThis is an aftermarket replacement, not an OEM component.\u003c\/li\u003e\n\u003cli\u003eProfessional installation is recommended for safety and performance.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eAbout Sea Sierra\u003c\/h2\u003e\n\u003cul\u003e\n\u003cli\u003ePro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.\u003c\/li\u003e\n\u003cli\u003eFast Global Fulfillment — Free standard delivery to most regions in 5–15 days.\u003c\/li\u003e\n\u003cli\u003eManufacturer-Direct Value — Fair pricing without compromising on materials or QC.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003c\/section\u003e","brand":"SeaSierra","offers":[{"title":"Default Title","offer_id":50723973923131,"sku":"SIE-17IY011","price":23.5,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0826\/8673\/8747\/files\/Water_Pump_Impeller_Kit_for_Yamaha_40HP-50HP_2-Stroke_6H4-W0078-00-00_-_JLM_MARINE-8289214.jpg?v=1763038930","url":"https:\/\/seasierra.com\/products\/water-pump-impeller-service-kit-fits-yamaha-2-stroke-40-50-hp-replaces-6h4-w0078-00-18-3408-18-3429","provider":"SeaSierra","version":"1.0","type":"link"}