Mercury - Water Pump Base to Face Plate Gasket - 27-39625
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
The Mercury Marine 27-39625 Water Pump Base to Face Plate Gasket is an OEM lower-unit cooling-system gasket used on compatible Mercury and Mariner outboards. It seals the joint between the water pump base and stainless face plate, helping the impeller maintain proper suction and raw-water pressure as cooling water is drawn through the lower unit and delivered upward to the powerhead.
Key Features
- Mercury part number: 27-39625
- Product type: Water pump base to face plate gasket
- Application location: Lower-unit water pump assembly
- Primary function: Seals the water pump base-to-face plate joint
- System: Outboard raw-water cooling system
- Material type: Paper-composite style water pump gasket
- Service use: Impeller replacement, water pump rebuild, lower-unit cooling service, and leak repair
- Aftermarket cross-reference: Sierra Marine 18-2828
- Aftermarket cross-reference: GLM Marine 31200
Application Compatibility
This gasket is intended for compatible Mercury and Mariner outboard lower units where the water pump parts diagram calls for 27-39625. It is used inside the water pump assembly between the base casting and the stainless wear/face plate.
Because Mercury and Mariner lower units vary by horsepower, model year, gearcase size, driveshaft housing, and serial number range, fitment should be confirmed by the outboard serial number and water pump diagram before ordering.
Serial Number Fitment Notice
Do not select this gasket by brand alone. Mercury outboards can use different water pump base gaskets depending on horsepower, gearcase family, and production range. Confirm the outboard serial number, water pump base style, face plate shape, bolt pattern, and parts diagram before installation.
If replacing an impeller kit, compare the new gasket to the original gasket and make sure all water passages and bolt holes match exactly.
When This Part Needs Replacement
Replace this gasket whenever the water pump base or face plate is removed. It should also be replaced during impeller service, water pump rebuilds, overheating diagnosis, or lower-unit cooling-system inspection.
A worn, torn, crushed, misaligned, or reused gasket can allow air or water leakage inside the pump assembly, reducing impeller efficiency and weakening the cooling-water supply to the engine.
Installation Notes
Clean the water pump base, stainless face plate, and surrounding lower-unit surfaces before installing the new gasket. Remove old gasket material carefully without gouging the aluminum or stainless sealing surfaces. Inspect the impeller, wear plate, pump base, key, cup, grommets, seals, and water tube alignment while the water pump is apart.
Install the gasket in the correct orientation so all bolt holes and water passages line up. Follow the Mercury service manual for water pump assembly order, fastener tightening, impeller vane direction, and any sealant instructions. After service, run the engine with proper water supply and confirm strong cooling-water flow.
Alternate/Cross-Reference Part Numbers
- Mercury Marine: 27-39625
- Sierra Marine: 18-2828
- GLM Marine: 31200
- Common description: Water Pump Base to Face Plate Gasket
- Application reference: Mercury / Mariner outboard lower-unit water pump gasket
Cross-reference numbers should be confirmed against the exact outboard model, serial number, and water pump parts diagram before substitution.
Parts Desk Insight
This gasket is inexpensive but important during impeller service. If the water pump is apart, replacing the base-to-face-plate gasket helps protect pump suction and cooling-water pressure. A weak seal at this joint can contribute to poor cooling performance even when the impeller itself is new.
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
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
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.