What It Does
The impeller is a rubber component in your outboard's lower unit that pumps raw water through the engine's cooling passages. Without a functioning impeller, the engine overheats in minutes. Impellers are wear items — replace annually or every 100 hours. The vanes harden, crack, and lose flexibility over time, reducing water flow before outright failure.
Failure Signs
- Overheating alarm or rising temp gauge
- Reduced tell-tale water stream from cowling
- Visible cracks or missing vanes on inspection
- Extended dry storage (vanes take a permanent set)
- Over 1 year or 100 hours since last replacement
Replacement
- Consult service manual for lower-unit removal procedure
- Pull old impeller, note vane direction
- Inspect housing liner for scoring — replace if worn
- Lubricate new impeller with impeller grease or dish soap
- Insert with vanes in correct rotation direction
- Reassemble, verify tell-tale stream on startup
Critical
Account for every broken vane when removing a failed impeller. Missing pieces may block cooling passages and cause overheating even with a new impeller.
Key Takeaway
Replace annually regardless of condition. A $15 impeller is cheap insurance against catastrophic engine damage. Always carry a spare aboard.
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Frequently Asked Questions
How often replace impeller?
Annually or every 100 engine hours, whichever comes first.