How to Winterize a Small Outboard Motor: The Complete Step-by-Step Guide
An hour of work in the fall decides whether your motor starts on the first warm spring morning or spends that morning in a repair shop. Here is every step, in the right order.
How to winterize a small outboard motor: flush the cooling system with fresh water, treat the fuel with stabilizer and run it through, drain or protect the fuel system, fog the cylinders, change the gear oil and engine oil, grease the fittings, look after the battery, and store the motor upright somewhere dry.
Hélène’s spring surprise, and the fall she got it right
The first year Hélène owned her 9.9 HP, she pulled it off the boat on Thanksgiving weekend, hung it on a stand in the shed and walked away. In May it would not start. The shop found gummed-up fuel in the carburetor and a lower unit full of milky gear oil where water had crept past a seal and sat all winter.
The bill was more than a full season of fuel. So the next fall she did it properly: a Saturday morning, a pot of coffee, a checklist, and the motor on a sawhorse stand beside a garden hose. It took just over an hour. In spring she added fresh gas, squeezed the bulb and it started on the second pull.
Winterizing is cheap insurance. Follow her full list below.
What are the steps to winterize a small outboard?
Do them in this order. Always follow your owner’s manual where it differs, since procedures vary by brand and fuel system.
- Treat the fuel first. Add marine fuel stabilizer to the tank at the dose on the bottle. Top up with fresh gas so less air sits in the tank.
- Flush and run. Attach flush muffs to a hose (or use the flush port, or a test barrel), turn the water on, then start the motor. Idle for 5 to 10 minutes so treated fuel reaches the carburetor or injectors and salt, silt and sand wash out. Confirm a strong tell-tale stream.
- Protect the fuel system. Carbureted models: disconnect the fuel line and let the engine run until it stalls, then open the float bowl drain screw to empty the carburetor, if your manual recommends it. EFI models: do not run dry; leave stabilized fuel in the system as the manual directs.
- Fog the engine. Spray fogging oil into the air intake at a fast idle until the engine smokes heavily, or remove the spark plugs, spray a short burst into each cylinder and turn the flywheel by hand a few times. Refit the plugs. On EFI motors, follow the manual; some advise against fogging through the intake.
- Change the engine oil and filter. Warm oil drains more completely. Old oil holds acids and moisture that attack bearings over a long, idle winter. Refill to the mark with the grade your manual specifies.
- Change the gear oil. Remove the lower drain screw, then the upper vent screw, and let it drain. Milky oil means water got in and a seal needs attention. Refill from the bottom hole with marine gear lube until it comes out the top, fit the top screw, then the bottom.
- Grease and inspect. Grease every fitting (swivel bracket, tilt tube, steering). Pull the propeller, check for fishing line around the shaft, grease the splines and refit with a new cotter pin if needed.
- Look after the battery. Disconnect it, clean the terminals, charge it fully and store it somewhere cool and dry. A maintainer or smart charger keeps it healthy until spring.
- Clean, drain and store. Wipe the cowling, touch up paint chips, and store the motor upright (vertical) so all water drains from the gearcase and cooling passages. Water trapped in a tilted motor can freeze and crack parts. Cover it loosely with a breathable cover.
What supplies do you need to winterize an outboard?
| Supply | Step | Small-motor quantity |
|---|---|---|
| Marine fuel stabilizer | 1 | Dose per the bottle for your tank size, in ml per litre or oz per gallon |
| Flush muffs + garden hose | 2 | One set sized for your lower unit |
| Fogging oil | 4 | One can covers several seasons |
| Engine oil + filter | 5 | About 0.25–1.8 L (0.3–1.9 qt), by model |
| Marine gear lube + pump | 6 | Usually under 0.5 L (about 1 pint) |
| Marine grease + gun | 7 | One cartridge |
| Battery charger or maintainer | 8 | One, for electric-start models |
Tools and motors that make next winter easier
EFI motors skip carburetor draining, and electric motors skip fuel entirely. Starting prices in USD.
How to winterize a small outboard motor: FAQ
When should I winterize my outboard?
Right after your last trip and before the first hard freeze. Water left in the gearcase or cooling passages can freeze and crack parts.
Should I drain the fuel or leave it stabilized?
Carbureted motors usually benefit from a drained carburetor. EFI systems are generally stored with stabilized fuel. Your owner’s manual has the final word.
Can I store a small outboard lying down?
Upright is best for winter, so water drains and oil stays in the sump. If space forces you to lay it down, use only the side the manual approves.
How long does winterizing take?
About 60 to 90 minutes for the full job the first time. With supplies ready, a basic version takes about 20 minutes; see our quick checklist.
Do electric outboards need winterizing?
Only lightly. Rinse and dry the motor, and store the lithium battery indoors at the charge level the manufacturer recommends, away from freezing temperatures.
Put it away right. Pull it out ready.
Motor past saving, or ready for an upgrade before spring? Tell us your boat and we will line up a replacement.