Mercury Verado L6 Water Pump Repair Kit 5.44" Gearcase - 8M0078858
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The Mercury Quicksilver 8M0078858 is a genuine Mercury Marine OEM water pump repair kit used on select high-horsepower Mercury Verado outboards. This kit services the raw-water pump assembly in the lower unit, helping restore proper cooling-water flow from the gearcase up to the powerhead.
It is commonly associated with select 6-cylinder Mercury Verado and related high-output applications using the 5.44-inch heavy-duty gearcase where the factory parts diagram calls for 8M0078858.
Key Features
- Genuine Mercury Marine OEM water pump repair kit.
- Mercury/Quicksilver part number: 8M0078858.
- UPC reference: 745061916265.
- Designed for select Mercury Verado outboards where specified.
- Used with select 5.44-inch heavy-duty gearcase applications.
- Services the lower-unit water pump assembly for proper raw-water cooling flow.
- Includes major water pump housing, impeller, gasket, seal, key, and carrier components where supplied in the factory kit.
- Important service kit for overheating prevention, weak telltale flow, seasonal maintenance, and lower-unit pump rebuilds.
Typical Kit Contents
Factory kit contents may include:
- Rubber water pump impeller
- Upper impeller housing
- Lower impeller housing
- Face plate
- Gaskets and seals
- Drive key
- Face seal
- Seal carrier reference 8M0046297
- Water tube coupling
- Related pump hardware and service components where supplied
Confirm the exact kit contents against the Mercury parts diagram and package before installation.
Engine Compatibility
Common application context includes select Mercury outboards where the factory lower-unit diagram calls for 8M0078858, including:
- Select Mercury Verado L6 / 6-cylinder outboards.
- Select 200 HP, 225 HP, 250 HP, 275 HP, 300 HP, 350 HP, and 400 HP Verado configurations where specified.
- Select Mercury Racing 400R applications where the parts diagram confirms this kit.
- Select outboards using the matching 5.44-inch heavy-duty gearcase water pump layout.
Use this kit only where the Mercury parts diagram specifically calls for 8M0078858.
Serial Number Fitment Notice
Confirm fitment by engine serial number, horsepower, gearcase size, lower-unit style, water pump housing layout, and factory Mercury parts diagram before ordering. Verado engines can use different pump kits depending on gearcase size, production range, and application. Do not select this kit by horsepower alone.
When This Part Needs Replacement
Replace the water pump components during scheduled lower-unit service or whenever the engine shows weak water flow, overheating, high operating temperature, poor telltale output, impeller damage, melted housing surfaces, cracked pump housings, worn gaskets, or suspected dry-run damage. The pump should also be serviced after long storage, sand or debris ingestion, or any lower-unit teardown where the pump assembly is removed.
Installation Notes
Inspect the driveshaft, pump base, housing surfaces, water tube, grommets, key, seals, and gearcase mating surfaces before installation. Install the impeller in the correct rotation and make sure the drive key is fully seated. Replace disturbed gaskets and seals rather than reusing compressed or torn components.
After installation, refill and inspect the lower unit as required, then run the engine on a proper water supply and confirm strong cooling-water flow and stable operating temperature before returning the boat to service.
Alternate/Superseded Part Numbers
- 8M0078858 — Mercury/Quicksilver OEM water pump repair kit
- 745061916265 — UPC reference
- 8M0046297 — seal carrier reference included in the supplied kit contents; verify by diagram
Parts Desk Insight
This kit should be matched by gearcase size and serial number, not just by Verado horsepower. The 5.44-inch heavy-duty gearcase uses a different pump layout than smaller gearcase configurations. For best results, inspect the water tube coupling, pump base, and driveshaft sealing area during the same service so the rebuilt pump can deliver full cooling flow.
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
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If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
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