Why It Matters
Salt crystallizes inside cooling passages as water evaporates, restricting flow, corroding components, and reducing cooling efficiency. A freshwater flush after every saltwater trip dissolves deposits before they set, extending engine life by years. Most modern outboards have a built-in flush port; older engines use flush muffs over the lower-unit intakes.
Step by Step
- Connect hose to flush port (or attach flush muffs)
- Turn on water to full flow
- Start engine, idle only — never rev during flush
- Run 5-10 minutes, watch tell-tale for steady clear flow
- Shut off engine FIRST, then water
- Lower engine to full-down to drain all passages
Common Mistakes
- Forgetting water before starting — dry-running damages impeller in seconds
- Revving during flush — idle only
- Skipping after 'just one trip' — salt damage is cumulative
- Leaving engine up after flush — trapped water corrodes or freezes
Key Takeaway
Water on before start, engine off before water off. 5-10 minutes at idle. Lower to drain. This 10-minute habit is the best outboard longevity investment.
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Frequently Asked Questions
How long to flush?
5-10 minutes at idle with fresh water flowing through flush port or muffs.