Mercury MerCruiser Quicksilver Water Pump Gear Housing Gasket 426311
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Mercury MerCruiser Quicksilver 27-426311 is an OEM-style water pump to gear housing gasket used in select Mercury and Mariner gear housing water pump assemblies. This gasket seals between the water pump base and gear housing, helping maintain proper cooling-water flow and reducing the risk of leakage at the pump mounting surface. Current Mercury parts references show 426311 superseding to 8M0204678 as the functional replacement.
Key Features
- Water pump to gear housing gasket for select Mercury, Mariner, and MerCruiser applications
- Used at the water pump base / gear housing sealing surface
- Supports proper water pump sealing during impeller or water pump service
- OEM reference number: 27-426311
- Current replacement reference: 8M0204678
- Lightweight gasket; catalog shipping reference for related 42631 listing shows approximately 0.02 lb with package dimensions around 3.75 in. x 2.78 in. x 0.25 in.
Engine Compatibility
This gasket is commonly shown in Mercury parts references for select Mercury and Mariner V6 outboard gear housing / water pump assemblies, including various Magnum II, Magnum III, V-135, V-150, V-150 EFI/DFI, V-200 EFI, V-220, XR-4, and related 2.4L / 2.5L applications depending on serial range. It is also cross-referenced in aftermarket listings for MerCruiser stern drive and Mercury Marine outboard water pump gasket applications.
Serial Number Fitment Notice
Mercury gasket fitment varies by engine model, gear housing, water pump base, and serial number range. Always confirm compatibility using the engine or drive serial number before ordering, especially where older part number 27-426311 has been replaced by 8M0204678.
When This Part Needs Replacement
Replace this gasket whenever the water pump base is removed, during impeller service, or when there are signs of leakage, gasket compression, tearing, or surface damage. Reusing a compressed gasket can lead to poor sealing and repeat cooling-system service.
Installation Notes
Clean the gear housing and water pump base mating surfaces before installation. Remove old gasket material carefully without gouging the aluminum surface. Install the gasket in the correct orientation and torque the water pump fasteners according to the Mercury service manual for the specific engine or drive model.
Alternate / Superseded Part Numbers
- 27-426311
- 426311
- 27-42631-1
- 27-42631
- 8M0204678
- 27-8M0204678
- Sierra 18-2919
- GLM 31050
- Mallory 9-60031
- OMC 0508835
- Redline RL2919
Parts Desk Insight
This is the kind of small gasket that is worth replacing during water pump service instead of reusing. The part number history can be confusing because 426311, 42631-1, and 8M0204678 are closely related references, so matching by serial number and water pump assembly is the safest way to avoid ordering the wrong gasket.
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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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