Mercury Water Pump Gasket 858524 – MerCruiser Alpha One & Outboard
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Mercury Water Pump Gasket 858524
Part Number: 858524 (Mercury catalog prefix: 27-858524)
Brand: Mercury Marine (Quicksilver OEM)
Official Product Type: Water Pump Gasket
System: Cooling System – Water Pump
Condition: New OEM
Supersession
Part 858524 supersedes older Mercury part number 27-32434. If your parts diagram or service manual references 27-32434, this is the current OEM replacement.
What It Does
This is the OEM water pump gasket used to seal the water pump housing during assembly on selected MerCruiser sterndrive and Mercury/Mariner outboard applications. Mercury recommends replacing all gaskets and seals any time the water pump is opened for impeller service — reusing a compressed or disturbed gasket risks a cooling system leak after reassembly.
Compatible Applications
- MerCruiser 1, R, MR, and Alpha One sterndrives — serial range 2495186 through 0D469858
- Mercury and Mariner 65 HP (4-cylinder) outboards with short-vane water pump impellers
- Mercury and Mariner V6 outboards with short-vane water pump impellers
Serial Number Note: Confirm compatibility using your exact engine or drive serial number in the Mercury Parts Catalog before ordering. Water pump components can vary by production serial range even within the same model family.
Diagram Position
This gasket is commonly referenced as the upper water pump gasket in MerCruiser Alpha One water pump assembly diagrams. Match the part number to the diagram position for your specific serial range before ordering.
Service Interval
Replace every time the water pump is opened — typically during impeller service every 3 years or 300 hours, whichever comes first, or whenever a cooling system issue is being diagnosed. Do not reuse the original gasket after disassembly.
Kit Contents
Single OEM water pump gasket. This is a individual gasket, not a complete kit. For a full water pump service, see the complete repair kits below.
Related Products
- Mercury MerCruiser Water Pump Rebuild Kit 817275K05
- Mercury MerCruiser Water Pump Repair Kit 89984T5
- Mercury MerCruiser Water Pump Repair Kit 8M0100527
- Mercury MerCruiser Water Pump Repair Kit 8M0100526
- Mercury MerCruiser Quicksilver Body/Impeller Kit 807151A14
- Mercury MerCruiser Water Pump to Gear Housing Gasket 27-85610
Technical FAQ
Q: Can I reuse this gasket after removing the water pump?
No. Mercury recommends replacing all gaskets and seals during every water pump service. A gasket that has been compressed and disturbed will not seal reliably when reinstalled.
Q: Does this gasket fit all Alpha One drives?
No — it fits Alpha One drives within serial range 2495186–0D469858. Drives outside this range may use a different gasket. Always verify by serial number in the Mercury Parts Catalog.
Q: Is this the same as the gear housing gasket?
No. This is the water pump housing gasket. The water pump-to-gear housing gasket is a separate part — see 27-85610.
Parts Desk Insights
Best Use Case: This gasket is the right call when you’re doing a standalone impeller replacement and want to do it properly without buying a full kit. It’s also useful when a kit is backordered and you need just the gasket to complete a job. Keep one on hand if you service Alpha One drives regularly — it’s an inexpensive part that prevents a costly cooling failure.
Common Mistakes: The most common error is skipping the gasket replacement during impeller service to save a few dollars, then dealing with a weeping water pump afterward. Another frequent issue is ordering by model name alone without checking the serial range — Alpha One drives span a wide production window and not all use the same gasket. Always cross-reference the serial number before ordering.
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.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.