Sierra Water Pump Kit 18-3431, Replaces Yamaha 6L2-W0078-00-00, Without Housing

The Sierra 18-3431 Water Pump Kit is a complete rebuild kit for Yamaha outboard cooling systems, designed to replace a worn or failing water pump assembly without needing a new housing. This kit is built for outboard, inboard, and sterndrive engines that use this pump configuration, giving boat owners a direct path to restoring proper cooling flow and preventing overheating damage to the powerhead.

Each kit includes the core wear components that typically fail first in a marine water pump: the impeller, the cup/insert, and the mounting bolts. The impeller compound is formulated by Sierra based on the size and application of this specific pump, so it is matched to the demands of the Yamaha outboard cooling system rather than a generic rubber blend. All other components in the kit are manufactured to meet or exceed original equipment specifications, so fit and performance align with the original design intent.

Because this kit is supplied without a housing, it is intended for engines where the existing pump housing is still serviceable and only the internal wear parts need replacement. The kit is assembled and quality-checked at Sierra's Illinois factory and is backed by Sierra's warranty.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3431
• Product Name: Water Pump Kit
• Configuration: Without Housing
• Weight: 0.44 pounds
• UPC: 030999975782
• Number of Items: 1
• Kit Contents: NSS Cup/Insert, Impeller (Sierra 18-3065), Bolts (4)

Fitment

• Yamaha outboard engines using the 6L2-W0078-00-00 water pump assembly

Replaces (OEM)

• 6L2-W0078-00-00

Frequently Asked Questions

What does the Sierra 18-3431 Water Pump Kit include? The kit contains an NSS cup/insert, an impeller (Sierra part 18-3065), and four mounting bolts, giving you the internal wear components needed to rebuild the water pump.

Does this kit come with a pump housing? No, the Sierra 18-3431 is supplied without a housing, so it is intended for use with an existing, still-serviceable pump housing.

What Yamaha part number does the 18-3431 replace? It replaces Yamaha OEM number 6L2-W0078-00-00.

How much does the water pump kit weigh? 0.44 pounds.

Is the impeller in this kit sized specifically for this pump? Yes, the impeller compound in the Sierra 18-3431 kit is formulated based on the specific size and application of this pump rather than being a generic universal impeller.

What engine types is the Sierra 18-3431 designed for? This water pump kit is offered for outboard, inboard, or sterndrive applications, specifically for Yamaha outboard engines that use the 6L2-W0078-00-00 pump assembly.

Where is the Sierra 18-3431 kit made? Sierra assembles this water pump kit at its factory in Illinois.

Is the Sierra 18-3431 backed by a warranty? Yes, it is backed by Sierra's warranty.

How many bolts come in the kit? Four bolts are included in the Sierra 18-3431 Water Pump Kit.

What is the UPC for this water pump kit? 030999975782 is the UPC for the Sierra 18-3431 Water Pump Kit.

Is the replacement impeller made to OEM specifications? The impeller and other components in the 18-3431 kit are constructed to meet or exceed original manufacturer specifications.