Mercury 27-39625 Water Pump Base-to-Face Plate Gasket – Lower
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The Mercury 27-39625 is a genuine OEM lower water pump gasket used in selected Mercury and Mariner outboard lower units. It installs between the water pump base and the stainless face plate, sealing that joint so the impeller maintains proper suction and cooling-water flow to the powerhead. One gasket is required per applicable water-pump assembly.
Compatible Applications
- Mercury 20 HP — from approximately serial number 1558310 and up
- Mercury 200 / 20 HP-series models — confirm by serial number range and water-pump diagram
- Any Mercury or Mariner lower unit where the water pump parts diagram calls for 27-39625
Always confirm fitment using the outboard model, horsepower, serial number, and the applicable water-pump parts diagram before ordering. Mercury uses different water-pump gasket shapes across lower-unit families.
Where It Fits – Assembly Stack
This gasket occupies the lower position in the water pump assembly stack:
- Water pump base (bottom)
- 27-39625 — this gasket (base-to-face plate)
- Face plate 39624 (stainless wear plate)
- 27-396231 / 27-39623 — upper face-plate-to-pump-body gasket
- Water pump body (top)
Do not confuse this lower gasket with 27-396231, which seals the upper side of the face plate to the pump body. They are separate parts and both should be replaced during a full water-pump service.
Product Details
- OEM Part Number: 27-39625
- Also Referenced As: 39625
- GTIN: 745061141346
- Factory Description: Gasket, Water Pump Base to Face Plate (Lower)
- Material: Paper-composite water pump gasket
- System: Outboard raw-water cooling / lower-unit water pump
- Quantity Required: 1 per water-pump assembly
When to Replace
Replace this gasket whenever:
- The water pump impeller is being serviced
- The water pump base or face plate is removed for any reason
- The old gasket is torn, compressed, swollen, or brittle
- Overheating or weak cooling-water flow is being diagnosed
- Leakage is found around the pump base during a lower-unit inspection
- The face plate or water pump base is being replaced
A new impeller can still deliver poor cooling performance if this gasket cannot maintain a proper seal at the pump base.
Installation Notes
Before installing the new gasket:
- Remove all traces of the old gasket from the pump base and face plate surfaces
- Clean the mating surfaces carefully — do not gouge aluminum or stainless sealing areas
- Inspect the face plate (39624) for scoring or wear
- Replace the upper gasket (27-396231) and the base-to-gear-housing gasket (27-39626) at the same time when doing a complete service
- Inspect the impeller, key, pump housing, and O-ring while the assembly is apart
Follow the applicable Mercury service manual for assembly sequence, impeller-vane orientation, fastener torque, and any required sealing compound. Do not reuse the old gasket or stack gaskets.
Alternate / Cross-Reference Part Numbers
- 27-39625 — Mercury OEM
- 39625 — short-form Mercury reference
- Sierra 18-2828 — aftermarket cross-reference
- GLM 31200 — aftermarket cross-reference
Cross-reference numbers should be verified against the outboard serial number and water-pump diagram before use as a substitute.
Related Parts
- Mercury MerCruiser Quicksilver Water Pump Repair Kit 8M0135821
- Mercury Quicksilver Heavy-Duty Water Pump Kit 8M0137849 – 15 & 20 HP EFI FourStroke
- Mercury Outboard Water Pump Impeller 8-Blade – 8M0135803
- Mercury Quicksilver Water Pump Base O-Ring 25-26722
Parts Desk Insights
Best Use Case: This is the right part to have on hand any time a customer is servicing the water pump on a Mercury or Mariner 20 HP outboard. At a few dollars, it’s inexpensive insurance during an impeller change — if the pump is already apart, replacing this gasket along with the upper gasket and base O-ring ensures the whole pump assembly seals correctly from the start.
Common Issues: The most common mistake is ordering only the impeller and skipping the gaskets. Mercury uses two separate gaskets above and below the face plate — 27-39625 below and 27-396231 above — and both should be replaced at the same time. If only one gasket is swapped, a leak at the unsealed joint can reduce cooling efficiency even with a brand-new impeller installed.
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.