Scope

Applies broadly to Yamaha F-series four-strokes (F25 through F350). Always confirm model-specific steps in the service manual — fuel system layouts differ between generations.

Why winterize an outboard at all

Outboards self-drain when vertical, so freeze cracks are rarer than with sterndrives — but fuel degradation, internal corrosion, and trapped water in the gearcase still kill engines over winter.

Step-by-step

1. Stabilize fuel. Dose the tank with a marine fuel stabilizer, then run the engine long enough (on muffs or on the water) to pull treated fuel through the VST and injectors. Ethanol-blend fuel left untreated is the biggest spring failure driver.
2. Change engine oil and filter warm. Acidic used oil sitting on bearings all winter is corrosive. Check the service manual for capacity and filter torque guidance.
3. Fog or mist protect. On EFI models, follow Yamaha's recommended storage procedure — some techs use fogging oil through the intake at fast idle until smoke, others use the manufacturer's storage-rinse routine. Do not fog engines where the manual prohibits it (oxygen-sensor-equipped models).
4. Change the gear oil now, not in spring. Drain from the lower plug, fill from the bottom until oil exits the vent. Milky oil = water intrusion; deal with seals before storage so water doesn't freeze inside the case.
5. Flush with fresh water, then let the engine drain fully in the vertical (down) position. Never store it tilted with water trapped in the exhaust housing.
6. Grease everything — prop shaft (pull the prop, check for fishing line at the seal), tilt tube, steering, linkage grease points.
7. Battery — disconnect, store on a maintainer.
8. Touch up paint nicks, spray corrosion inhibitor under the cowl, and replace anodes worn past roughly half.

Common mistakes

• Storing the engine tilted up outdoors (traps rainwater and freeze-cracks the exhaust housing)
• Stabilizer poured in but never run through the engine
• Skipping the gear oil check and discovering milk in April — too late for the seal warranty conversation

When to walk away

If you find milky gear oil plus a fishing-line-scored seal on a late-model engine under warranty, document and refer to a dealer rather than opening the case yourself.

Safety: run on muffs with good water supply only, keep clear of the prop, and ventilate when handling fuel and fogging oil.