Mercury MerCruiser Seawater Pump Gasket 27-34897 — Pack of 2
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Mercury MerCruiser Seawater Pump Gasket — Part No. 27-34897 | Pack of 2
This listing is for a pack of 2 genuine Mercury Marine OEM seawater pump gaskets, part number 27-34897 (base number 34897). This gasket seals the seawater pump housing to the engine mounting surface on compatible GM-based MerCruiser V6 and V8 engines, preventing cooling-water leaks at the pump and supporting proper raw-water flow through the cooling system. Having two on hand is practical — one for the current service and one for the next, or as a spare if the first is damaged during installation.
Part Details
- Part Number: 27-34897
- Base Number: 34897
- Pack Quantity: 2 gaskets per listing
- Type: Seawater Pump Housing Gasket
- System: Raw-water (seawater) cooling circuit
- Type: Genuine Mercury Marine OEM replacement gasket
Compatible Applications
- MerCruiser 4.3L V6 — GM-based, seawater pump housing location per diagram
- MerCruiser 5.0L / 305 CID V8 — per diagram
- MerCruiser 5.7L / 350 CID V8 — per diagram
- MerCruiser 6.2L / 377 CID V8 — per diagram
- MerCruiser 350 MAG — per diagram
- MerCruiser 300 Tempest — per diagram
- MerCruiser 320 EFI — per diagram
- MerCruiser 280 TRS — per diagram
- Select MerCruiser ski engine configurations — where diagram specifies 27-34897
Confirm fitment by engine serial number, seawater pump style, and parts diagram before ordering. Pump gasket fitment can vary by engine block, pump housing design, cooling-system layout, and production range.
Alternate, Superseded & Interchange Part Numbers
- 27-34897 — current Mercury/MerCruiser formatted number
- 34897 — base part number
- 2734897 — alternate Mercury reference format
- BRP / OMC 3852477 — OEM cross-reference
- Sierra Marine 18-0891 — aftermarket interchange
- Mallory Marine 9-61600 — aftermarket interchange
- GLM Products 31380 — aftermarket interchange
Related Parts
- Mercury MerCruiser Seawater Pump Kit Without Air Fittings 8M0139995
- Mercury MerCruiser Seawater Pump Impeller Kit 8M0137219
- Mercury MerCruiser Body/Impeller Kit 807151A14
- Mercury MerCruiser Impeller Kit 8M0104229
Service Interval
Replace this gasket every time the seawater pump is removed for service. Gaskets that have been compressed and heat-cycled should never be reused — even if they appear undamaged. The seawater pump impeller is typically serviced annually or every 100 hours; replacing the pump gasket at the same time adds no meaningful cost and eliminates the risk of a leak after reassembly.
When to Replace
Replace if the gasket is torn, compressed flat, leaking, brittle, cracked, or damaged during pump removal. Also replace any time the seawater pump is removed for impeller service, pump replacement, or cooling-system diagnosis — do not reinstall a used gasket.
Installation Tips
- Clean the pump housing and engine mounting surfaces thoroughly before fitting the new gasket — old gasket material left on the surface will cause leaks
- Do not use sealant on this gasket unless specifically called for in the Mercury service manual for the application
- Inspect the pump housing, impeller, pulley alignment, and surrounding hoses while the pump is off
- Torque the pump mounting fasteners to the Mercury service specification — over-tightening can crush the gasket and cause leaks
- Run the engine and check for leaks at the pump mounting surface after reassembly
Technical FAQ
Q: Why does this listing include 2 gaskets?
A: Having a spare on hand is practical for seawater pump service. If the first gasket is damaged during installation, or if you service multiple engines, the second gasket is ready without a separate order. It also makes sense to keep one in the spares kit for the next annual service.
Q: Can I use a Sierra 18-0891 or GLM 31380 instead?
A: Sierra 18-0891, Mallory 9-61600, and GLM 31380 are listed aftermarket interchanges for this gasket. For OEM fitment confidence, the Mercury 27-34897 is the factory-specified part.
Q: Do I need to replace the gasket if the pump isn’t leaking?
A: Yes, if the pump has been removed. A gasket that has been disturbed may not reseal reliably. At this price point, replacing it is always the right call when the pump is already off.
Parts Desk Insights
Best use case: This gasket is the right add-to-cart item any time a customer is ordering a seawater pump impeller kit, pump body kit, or full pump assembly for a GM-based MerCruiser V6 or V8. It should be replaced every time the pump comes off, and the pack-of-2 format makes it easy to keep a spare on hand for the next service. Pairing it with an impeller kit covers the full pump service in one order.
Common issues: The most frequent problem is customers reinstalling the original gasket after pump service, then discovering a cooling-water leak at the pump mounting surface shortly after. A used gasket that has been compressed and heat-cycled will not seal as reliably the second time. The other common issue is not cleaning the mounting surface before installation — old gasket material or corrosion on the surface prevents a proper seal even with a new gasket.
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
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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:
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