Water Pump Impeller Kit 393630 for Evinrude/Johnson Outboards
Updated June 10, 2026
This water pump impeller kit (OEM 393630) is a repair component for Evinrude and Johnson outboard motors in the 20 to 35 horsepower range. It replaces the worn impeller and drive key to restore proper cooling water flow through the engine. The kit is designed for 2-cylinder, 2-cycle engines with through-hub exhaust and fits most models from 1980 to 2005.
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How It Works
The water pump impeller is a flexible neoprene rotor that sits inside the lower unit housing. As the engine runs, the crankshaft drives the impeller via a metal key. The impeller blades rotate, creating suction that draws lake or ocean water into the cooling system. This water travels through passages in the powerhead to dissipate heat, then exits through the exhaust. A worn impeller reduces water flow, leading to overheating.
Common Failure Symptoms
Overheating is the primary symptom of a failing impeller – the engine may sputter, lose power, or trigger a warning alarm. Other signs include a weak or absent tell-tale stream, visible steam or smoke from the engine, and discoloration of paint near the exhaust. If the drive key shears, the impeller will not spin, causing immediate overheating.
Installation Notes
Installation requires removing the lower unit and disassembling the water pump housing. Replace the impeller, key, and all gaskets or seals included in the kit. Ensure the impeller blades are oriented correctly – they should curve in the direction of rotation. Lubricate the impeller with dish soap or glycerin during assembly. Torque bolts to manufacturer specifications. Do not reuse a worn housing; some kits include a new housing.
