Impeller Gaskets Pack of 2 | Sierra 18-2566-9
Impeller Gaskets Pack of 2 | Sierra 18-2566-9
Sierra
26 in stock
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Sierra 18-2566-9 Water Pump Impeller Gaskets | Pack of 2 | Replaces Mercury Marine 27-817277
The Sierra #18-2566-9 is a pack of two water pump impeller gaskets for Mercury Marine applications. Seals the water pump housing at the impeller service points. Replaces Mercury Marine 27-817277. Sold as a pack of 2.
Product Details:
- Part Number: 18-2566-9 (Sierra)
- SKU: SIERRA-18-2566-9
- Manufacturer: Sierra
- Type: Water Pump Impeller Gasket
- Pack: 2 gaskets
- Condition: New
Cross-Reference — Replaces:
- Mercury Marine: 27-817277
Additional Information
Water Pump Housing Gasket — Replace at Every Impeller Service:
The impeller gasket seals the water pump housing cover or base plate to prevent raw water bypass around the impeller. A failed or reused gasket allows water to bypass the impeller, reducing cooling flow and causing engine overheating even with a new impeller installed. Replace both gaskets in the pack at every impeller service — do not reuse old gaskets. Compressed gaskets that appear intact will leak after reassembly due to compression set.
Pack of 2 — Coverage:
The 18-2566-9 is sold as a pack of 2 gaskets. Depending on your water pump configuration, the kit covers one or two pump gasket positions per service. Keep a spare pack on board for emergency impeller service.
Installation Notes:
- Replace at every impeller service — do not reuse old gaskets
- Clean housing mating surfaces before installing new gaskets
- Do not use gasket sealant unless specified in the engine service manual
- Torque housing fasteners to specification per the Mercury Marine service manual
Frequently Asked Questions
1. How many gaskets are included?
Two gaskets per pack.
2. Should I replace the gaskets every time I replace the impeller?
Yes — always replace the gaskets at every impeller service. Reused gaskets that appear intact will leak after reassembly due to compression set from previous torque cycles.
3. What Mercury Marine part number does this replace?
Mercury Marine 27-817277.
! Compatibility references are provided for informational purposes only and do not constitute a fitment guarantee. Part numbers, application listings, and "replaces" cross-references are based on manufacturer data and are intended as a starting point for identification — not a guarantee of fit for your specific engine, hull, or installation.
Buyer is solely responsible for verifying compatibility with their engine model, serial number, model year, and trim configuration before purchase. If you are unsure whether this part fits your application, contact MacombMarineParts.com before you buy — we're available via text, email, or online chat to help verify compatibility for your specific application.
MacombMarineParts.com is not liable for parts ordered based on assumed fitment. Returns due to buyer-selected incorrect fitment are subject to our standard return and restocking fee policies.