Water Pump Gasket – Fits Mercruiser Alpha One (Replaces 27-858524)
Water Pump Gasket – Fits Mercruiser Alpha One (Replaces 27-858524) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Water Pump Gasket – Fits Mercruiser Alpha One (Replaces 27-858524)
Product Details
This Water Pump Gasket – Fits Mercruiser Alpha One (Replaces 27-858524) creates a vital seal between the water pump housing and the wear plate. It is specifically designed for Mercruiser Alpha One sterndrives (1983–1990) and various Mercury 2.5L V6 outboard engines.
It serves as a direct replacement for Mercury/Mercruiser 27-858524 and interchanges with Sierra 18-2915, GLM 31020, Mallory 9-60035, and OMC 0508837. This part also supersedes several previous part numbers, including 27-32434, 27-85609, 27-856091, 27-30604, and 27-85609B1.
- Installs between the pump housing and wear plate.
- This is a non-returnable, non-refundable OEM Mercury part.
- Sold in packages containing a quantity of five gaskets.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Mercury/Mercruiser | 27-858524 | Primary OEM Reference |
| Mercury/Mercruiser | 27-32434 | Superseded by 27-858524 |
| Mercury/Mercruiser | 27-85609 | Superseded by 27-858524 |
| Mercury/Mercruiser | 27-856091 | Superseded by 27-858524 |
| Mercury/Mercruiser | 27-30604 | Superseded by 27-858524 |
| Mercury/Mercruiser | 27-85609B1 | Superseded by 27-858524 |
| Sierra | 18-2915 | Aftermarket Interchange |
| GLM | 31020 | Aftermarket Interchange |
| Mallory | 9-60035 | Aftermarket Interchange |
| OMC | 0508837 | Aftermarket Interchange |
| Redline | RL2915 | Aftermarket Interchange |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercruiser applications, this gasket fits various Alpha One sterndrive and transom assemblies from 1983 to 1990.
| Brand | Model | Years | OEM Part No. | Notes |
|---|---|---|---|---|
| Mercruiser | Alpha One (Gen I) | 1983–1990 | 27-858524 | Fits between pump housing and wear plate |
| Mercruiser | Alpha One SS (High Performance) | 1986–1989 | 27-858524 | |
| Mercruiser | R/MR/Alpha One (Sterndrive) | 1983–1990 | 27-858524 | |
| Mercruiser | R/MR/Alpha One (Transom Assembly) | 1983–1990 | 27-858524 |
For Mercury outboards, this gasket is used on a wide range of 2.5L V6 engines, including carbureted, EFI, and DFI models.
| Brand | Model | Rated HP | OEM Part No. | Notes |
|---|---|---|---|---|
| Mercury | V-135, V-140, V-150, V-200 | 135-200 | 27-858524 | 2.5L Carbureted models |
| Mercury | V-135 DFI | 135 | 27-858524 | 2.5L DFI engine |
| Mercury | XR-6 | 27-858524 | 2.5L engine | |
| Mercury | MAGNUM III | 27-858524 | 2.5L engine | |
| Mercury | 110 Jet | 110 | 27-858524 | 2.5L DFI engine |
| Mercury | 140 JET | 27-858524 | 2.5L engine | |
| Mercury | 150 Pro XS | 150 | 27-858524 | 2.5L engine |
| Mercury | V-150 EFI | 150 | 27-858524 | 2.5L EFI engine |
| Mercury | 175 PROXS | 175 | 27-858524 | 2.5L engine |
| Mercury | V-175 DFI | 175 | 27-858524 | 2.5L DFI engine |
| Mercury | 200XS SST | 200 | 27-858524 | |
| Mercury | 200XS DFI | 200 | 27-858524 | 2.5L DFI engine |
| Mercury | 225 EFI PRO MAX/SUPER MAG | 225 | 27-858524 | |
| Mercury | 225X EFI PROMAX | 225 | 27-858524 |
Technical Specs
- Product Type
- Water Pump Gasket
- Installation
- Between pump housing and wear plate
- Length
- 1.06 in
- Width
- 7.5 in
- Height
- 6.0 in
- Weight
- 0.01 kg (0.022 lb)
- Packaging
- Must be sold in quantities of 5
- OEM Requirements
- Non-returnable, non-refundable OEM Mercury part
What’s in the Box
- 5 x Water Pump Gaskets (27-858524)
Installation Notes
- Disconnect the negative battery cable before beginning work.
- Access the lower unit's water pump assembly according to your service manual.
- Carefully remove the old water pump gasket and wear plate. Thoroughly clean any remaining gasket material or corrosion from the mating surfaces.
- Position the new gasket correctly on the water pump housing.
- Place the wear plate over the new gasket, ensuring alignment.
- Reassemble the water pump and lower unit, torquing all fasteners to the manufacturer's specified values.
Troubleshooting & FAQ
How do I know if this gasket will fit my engine?
Please review the Engine & Model Compatibility tables on this page. Cross-reference your engine's brand, model, and year range to ensure a match. Verifying the OEM part number (27-858524) in your service manual is the most reliable method.
What are the signs of a failing water pump gasket?
Common symptoms include engine overheating at idle or low speeds, a weak or non-existent "tell-tale" water stream, or visible water leakage around the lower unit's seams. These indicate a loss of sealing pressure in the cooling system.
Why is this part sold in a package of five?
This OEM part is packaged by the supplier in quantities of five. This is convenient for marine service shops that perform frequent repairs or for boat owners who wish to keep spares on hand for future maintenance.
Is this part returnable if it doesn't fit?
No. Per vendor policy for OEM-sourced components, this part is non-returnable and non-refundable. We strongly recommend you verify compatibility with your specific engine model before purchasing.
Can I reuse my old gasket after inspecting it?
No. Gaskets are single-use components that compress and deform to create a seal. Reusing an old gasket will almost certainly lead to leaks and can cause engine damage from overheating. Always use a new gasket during assembly.
OEM vs. Aftermarket?
This 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.
Shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
Covered 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 & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
Payment & Security
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