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Outboard engine: winterisation step by step
CalosGroup editorial team · Published on 3 November 2026
Fresh-water flush, gearcase oil, spark plugs, fuel and impeller: how to prepare your outboard for winter so it is ready in spring.
Winterisation is when most of the next season's failures are prevented: salt, old fuel and water left in the engine are the main enemies.
What you need
Gearcase oil, drain plug seals, spark plugs, fuel stabiliser, protective spray oil, marine grease. For the water pump impeller, if it needs replacing, the one specified by the manufacturer.
Always follow your engine's manual: oil types, torques and intervals differ from brand to brand.
The steps
- Flush the engine with fresh water using the «earmuffs» or the flushing connector, running it at idle until the water comes out clean.
- Drain the fuel system or add stabiliser to the tank and run the engine for a few minutes so it reaches the carburettor or injectors.
- Change the gearcase oil: remove the lower plug first and then the upper one; if the oil comes out milky, water has got in and the seals must be checked.
- Remove the spark plugs, spray a little protective oil into the cylinders, turn the engine over by hand a few times and fit new plugs.
- Check the water pump impeller and replace it if it has hardened or its vanes are damaged.
- Grease the specified points, check the sacrificial anode and replace it if worn.
- Store the engine upright, in a dry place, with the battery disconnected and charged.
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