Sierra 18-0563 Water Tube Rubber Seal - OEM 26-36556 for Mercury/Mariner Outboard Motors

The Sierra 18-0563 is a rubber water tube seal engineered for Mercury and Mariner outboard motor cooling systems. This small but essential seal fits over the water tube where it passes between the powerhead and the lower unit, maintaining a watertight connection so raw water can travel through the cooling passages without leaking or allowing air intrusion. A worn, cracked, or hardened water tube seal is a common cause of overheating and cooling system leaks on outboard motors, and replacing it is a routine part of a lower unit reinstall or water pump service.

Made from rubber for a durable, flexible seal against the water tube, the 18-0563 is manufactured to match OEM dimensions and cross-references directly to Mercury Marine part 26-36556, so it installs as a direct replacement without modification. Its compact size (0.39 x 0.39 x 0.39 inches) and light weight make it an inexpensive, easy-to-stock spare for anyone performing water pump impeller replacement or lower unit maintenance on compatible Mercury/Mariner outboards.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0563
• Product Category: Mercury Outboard Cooling System
• Material: Rubber
• Product Dimensions: 0.39 x 0.39 x 0.39 inches
• Weight: 0.01 pounds
• UPC: 030999874627
• OEM Cross-Reference: Mercury Marine 26-36556

Fitment

Fits Mercury/Mariner outboard motors that use Mercury Marine water tube seal 26-36556.

Replaces (OEM)

• 26-36556

Frequently Asked Questions

What does the Sierra 18-0563 water tube seal fit? The Sierra 18-0563 is designed for Mercury and Mariner outboard motors that use Mercury Marine water tube seal 26-36556.

Is the 18-0563 the same as Mercury part 26-36556? Yes, the Sierra 18-0563 cross-references directly to Mercury Marine part number 26-36556 and installs as a direct replacement.

What material is the 18-0563 seal made from? It is made from rubber, which provides the flexibility needed to seal tightly around the water tube.

How big is the Sierra 18-0563 water tube seal? The seal measures 0.39 x 0.39 x 0.39 inches and weighs 0.01 pounds, making it a small, lightweight component.

When should this water tube seal be replaced? The 18-0563 should be replaced when it is cracked, hardened, or leaking, and it is commonly replaced during a lower unit reinstall or water pump impeller service on Mercury/Mariner outboards.

Can a bad water tube seal cause overheating? Yes, a worn or damaged water tube seal like the 18-0563 replacement can allow air intrusion or coolant leakage that leads to overheating in the outboard cooling system.

Is the Sierra 18-0563 an OEM or aftermarket part? The 18-0563 is an aftermarket seal manufactured by Sierra to the same specifications as Mercury Marine OEM part 26-36556.

Does the 18-0563 come with installation hardware? No, the 18-0563 is the rubber water tube seal only; no additional hardware is included.

How do I know if I need the 18-0563 versus a different seal? Confirm your outboard uses Mercury Marine water tube seal 26-36556; the Sierra 18-0563 is the direct match for that part number.

Is the 18-0563 seal reusable after removal? Water tube seals like the 18-0563 are generally replaced rather than reused once removed, since they can lose their sealing shape during disassembly.