Mercury - Sea Water Pump Gasket - 27-881603001
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The Mercury MerCruiser Quicksilver 27-881603001 Sea Water Pump Gasket is an OEM replacement gasket for select high-displacement MerCruiser sterndrive and Mercury inboard marine engines. It seals the engine-mounted sea water pump interface in the raw-water cooling circuit, helping maintain pump suction, raw-water flow, and leak-free operation. This gasket is commonly serviced when the sea water pump is removed for impeller replacement, pump inspection, leak repair, or cooling-system maintenance on 8.1L / 496 big-block marine engine applications.
Key Features
- Mercury / Quicksilver part number: 27-881603001
- Short reference number: 881603001
- Superseded reference: 881603
- Product type: Sea water pump gasket
- Application location: Engine-mounted sea water pump sealing interface
- System: Raw-water cooling circuit
- Primary function: Seals the pump housing/mounting joint to help prevent water leakage and maintain pump efficiency
- Material type: Marine cooling-system composite gasket material
- Service use: Sea water pump removal, impeller service, cooling-system leak repair, and pump reseal work
- OEM status: Genuine Mercury MerCruiser / Quicksilver replacement gasket
Engine Compatibility
This gasket is intended for select GM-based big-block Mercury MerCruiser and Mercury inboard engines where the parts diagram calls for 27-881603001, including:
- MerCruiser MCM 496 MAG
- MerCruiser MCM 496 MAG HO
- Mercury MIE 8.1S
- Mercury MIE 8.1S HO
- Mercury / MerCruiser 8.1L TowSport applications where specified
Fitment must be confirmed by engine serial number, model designation, cooling-system layout, and Mercury parts diagram.
Serial Number Fitment Notice
Mercury cooling-system gaskets are serial-number specific. Confirm the engine serial number before ordering, especially on 8.1L / 496 engines where raw-water pump design, cooling configuration, and pump mounting details can vary by model and production range.
Do not select this gasket by displacement alone. Match the gasket to the exact Mercury diagram callout for 27-881603001 or the superseded reference 881603.
When This Part Needs Replacement
Replace this gasket whenever the sea water pump is removed from the engine. It should also be replaced if there are signs of raw-water leakage around the pump mounting area, salt deposits, corrosion trails, water staining, reduced cooling flow, overheating, or seepage after previous pump service.
A used sea water pump gasket should not be reused after disassembly. Compression set, heat cycling, saltwater exposure, and old gasket residue can prevent it from sealing correctly a second time.
Installation Notes
Clean the pump and engine-side mating surfaces before installing the new gasket. Remove old gasket material carefully without gouging the sealing faces. Inspect the sea water pump body, impeller, wear plate, seals, shaft, mounting fasteners, hoses, clamps, and related cooling passages while the pump is apart.
Install the gasket in the correct orientation so all bolt holes and water passages align properly. Follow the Mercury MerCruiser service manual for gasket placement, fastener torque, impeller installation, pump priming, and leak testing. After reassembly, run the engine with proper water supply and confirm strong raw-water flow and no leaks at the pump.
Alternate/Superseded Part Numbers
- Current Mercury / Quicksilver number: 27-881603001
- Short reference: 881603001
- Superseded Mercury reference: 881603
- Common description: Sea Water Pump Gasket
- Application reference: Select MerCruiser 496 MAG / 496 MAG HO and Mercury MIE 8.1L sea water pump applications
Parts Desk Insight
This gasket is a small but important part of the sea water pump service. If the pump is being removed for an impeller or cooling-system repair, replacing the gasket during reassembly helps protect pump suction and prevents repeat leaks at the engine-mounted pump joint.
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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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