Mercury Verado L6 Water Pump Repair Kit – 5.44" Heavy-Duty Gearcase | 8M0078858
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Mercury Verado L6 Water Pump Repair Kit – 5.44" Heavy-Duty Gearcase | 8M0078858
Part Number: 8M0078858 | Gearcase: 5.44" Heavy-Duty | UPC: 745061916265
This is the genuine OEM water pump repair kit for the lower-unit raw-water cooling pump on Mercury Verado L6 outboards equipped with the 5.44-inch heavy-duty gearcase. The water pump is the heart of the engine’s cooling system — it draws water from below the waterline and delivers it to the powerhead. This kit provides all the components needed to restore full cooling-water flow during scheduled service or after pump failure.
Product Details
- Part Number: 8M0078858
- UPC: 745061916265
- Gearcase Size: 5.44" Heavy-Duty
- Engine Family: Mercury Verado L6 (6-cylinder supercharged 4-stroke)
- System: Raw-water cooling – lower unit water pump
- Weight (packaged): approx. 1.5 kg
Compatible Applications
- Mercury Verado L6 (6-cylinder) outboards with 5.44" heavy-duty gearcase
- Mercury Verado 200 HP (where diagram-confirmed for this gearcase)
- Mercury Verado 225 HP (where diagram-confirmed for this gearcase)
- Mercury Verado 250 HP (where diagram-confirmed for this gearcase)
- Mercury Verado 275 HP (where diagram-confirmed for this gearcase)
- Mercury Verado 300 HP (where diagram-confirmed for this gearcase)
- Mercury Verado 350 HP (where diagram-confirmed for this gearcase)
- Mercury Verado 400 HP (where diagram-confirmed for this gearcase)
- Mercury Racing 400R (where diagram-confirmed for this gearcase)
- Fitment is determined by gearcase size and serial number — not horsepower alone. Always verify using your engine’s exact serial number and the Mercury parts diagram before ordering.
Kit Contents
This factory kit typically includes:
- Rubber water pump impeller
- Upper impeller housing
- Lower impeller housing / face plate
- Gaskets and seals
- Drive key
- Face seal
- Seal carrier (ref. 8M0046297 — verify by diagram)
- Water tube coupling
- Related pump hardware and service components
Confirm exact contents against the Mercury parts diagram and package label before installation.
Service Interval
Mercury recommends replacing the water pump impeller every 300 hours or 3 years, whichever comes first. The full pump kit should be serviced during any lower-unit teardown where the pump assembly is removed, after sand or debris ingestion, or following any dry-run event. Do not wait for overheating symptoms — impeller vanes can crack or harden without visible external signs.
When to Replace
- Weak or absent tell-tale (pee-hole) water flow
- Elevated operating temperature or overheating alarm
- Visible impeller damage, cracking, or missing vanes
- Melted or distorted pump housing surfaces
- Worn or torn gaskets and seals
- Suspected dry-run damage
- Long-term storage without prior service
Installation Notes
Before installation, inspect the driveshaft, pump base, housing mating surfaces, water tube, grommets, drive key, and gearcase sealing areas for wear or damage. Install the impeller in the correct rotational direction and ensure the drive key is fully seated. Always replace disturbed gaskets and seals — do not reuse compressed or torn components. After reassembly, run the engine on a proper water supply and confirm strong cooling-water flow and stable operating temperature before returning to service.
Related Parts
- Mercury Water Pump Repair Kit 8M0100526
- Mercury Water Pump Repair Kit 8M0100527
- Mercury MerCruiser Quicksilver Impeller Kit 8M0104229
- Mercury Water Pump Repair Kit 8M0135821
- Mercury Quicksilver 300-Hour Service Kit 8M0133617 – L6 Verado
- Mercury MerCruiser Quicksilver 100-Hour Service Kit 8M0120657
- Sierra 9250 Outboard Maintenance Kit – Mercury 350–400 HP Verado 6-Cylinder
- Mercury Antifreeze – for cooling system flush and storage
- Browse all Mercury MerCruiser Cooling System Parts
- Browse all Water Pump Kits
- Browse all Mercury MerCruiser Engine Maintenance Parts
Parts Desk Insights
Best use case: This kit is the correct choice for a full water pump rebuild on a Verado L6 with the 5.44-inch heavy-duty gearcase. It’s well-suited for 300-hour or 3-year preventive maintenance, post-storage service, or any lower-unit job where the pump is being opened. Customers doing a complete lower-unit service should also inspect the driveshaft seals, water tube grommet, and shift shaft seal while the unit is apart — replacing those at the same time avoids a repeat teardown. Pairing this kit with the Verado L6 300-Hour Service Kit (8M0133617) covers the full scheduled maintenance scope in one order.
Common mistakes: The most frequent error is selecting a Verado water pump kit by horsepower rating without confirming the gearcase size. Verado engines in the same HP range can use different gearcases depending on production year and application, and pump kits are not interchangeable between gearcase sizes — always verify with the Mercury parts diagram using the engine serial number. A second common mistake is reusing the old drive key: if it’s worn or rounded, it will allow the impeller to slip on the driveshaft and the new kit will fail prematurely. Replace the drive key every time.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
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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