Sierra 18-3006 Neoprene Water Pump Impeller with 6 Fins - Johnson/Evinrude 40 HP 1971-73

The Sierra 18-3006 is a neoprene water pump impeller built for Johnson/Evinrude outboard motors, specifically the 40 HP models from 1971-73. This impeller is the core wear component of the outboard's water pump, drawing raw water from the intake and pushing it through the cooling system to keep the powerhead running at a safe temperature. Made from neoprene, it is molded with 6 fins that flex and reseat against the pump housing as the drive shaft turns, creating the pumping action that circulates cooling water. Neoprene is chosen for this application because it resists the heat, fuel exposure, and constant flexing that a water pump impeller experiences in service, while holding its shape for a consistent seal against the pump housing.

Sierra engineers and manufactures this impeller to meet or exceed original equipment quality, so it installs and performs as a direct replacement in the applications listed. Replacing a worn or cracked impeller at recommended service intervals helps prevent overheating, which can otherwise lead to costly powerhead damage. This impeller is sold individually and is intended to be installed as part of a routine water pump service or rebuild.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3006
• Product Type: Water Pump Impeller
• Material: Neoprene
• Color: White
• Number of Fins: 6
• Weight: 0.06 pounds
• OEM Cross-Reference: OMC 378891, 775521

Fitment

• Johnson/Evinrude 40 HP, 1971-73

Replaces (OEM)

• OMC 378891
• OMC 775521

Frequently Asked Questions

What engines does the Sierra 18-3006 impeller fit? The 18-3006 is built for Johnson/Evinrude outboard motors in the 40 HP application from 1971-73.

What is the 18-3006 impeller made of? It is molded from neoprene, a material chosen for its resistance to heat and flexing inside a marine water pump.

How many fins does this impeller have? The Sierra 18-3006 has 6 fins that create the pumping action drawing raw water through the outboard's cooling system.

Does the 18-3006 cross-reference to an OEM part number? Yes, it is equivalent to OMC 378891 and OMC 775521.

Is the Sierra 18-3006 an OEM part or an aftermarket replacement? It is a Sierra-manufactured aftermarket impeller built to meet or exceed original equipment quality, not an OMC-branded part.

How much does the 18-3006 impeller weigh? It weighs 0.06 pounds.

What color is the Sierra 18-3006 impeller? It is white, the natural color of the neoprene compound it is molded from.

Can the 18-3006 be used on any Johnson/Evinrude outboard? No, fitment is specific to the 40 HP 1971-73 application; buyers should confirm their engine model and year before ordering since Sierra lists different impeller part numbers for other years and horsepower ranges.

How often should a water pump impeller like the 18-3006 be replaced? A neoprene impeller such as the 18-3006 is a wear item that should be replaced whenever it shows cracking, worn fins, or reduced water flow, or as part of routine water pump service.

What happens if I run my outboard with a worn 18-3006 impeller? A worn impeller reduces raw water flow through the cooling system, which can cause the outboard to overheat and potentially damage the powerhead.

Does the 18-3006 come with the water pump housing or gaskets? No, the 18-3006 is the neoprene impeller only.