Maintenance
How to Winterize an Outboard
Winterizing protects an outboard from three things over the off-season: water freezing inside it, fuel going stale, and corrosion on parts that sit still for months. Most of the job takes one afternoon in the driveway. Engine makers disagree on two steps, fuel level and fogging, so the table below shows what each one says.
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Stabilize fresh fuel
Start with fresh fuel and add stabilizer at the storage rate on its label (see the section below). How full to leave the tank depends on the maker and the tank, so check the table under these steps. Work outdoors, away from sparks and flames, and wipe up any spill before you start the motor.
Run the treated fuel through
Run the motor so treated fuel reaches the whole fuel system, in the water or on a garden hose with flush muffs. Mercury and Yamaha both give about 10 minutes; your manual has the figure and the hose procedure for your model. Turn the water on before you start the motor and shut it off if the water stops or the overheat alarm sounds. Run it outdoors only, because the exhaust carries carbon monoxide, stay with it, and keep everyone clear of the prop.
Change the engine oil and filter (four-stroke)
Mercury lists a full oil and filter change before storage. Let the engine cool enough to handle, catch the old oil in a pan and take it to a used-oil collection point. Your owner's manual gives the oil type, the capacity, the filter and the drain plug torque.
Fog the engine
Fogging oil coats the cylinders, pistons and bearings to help keep moisture and rust off them while the motor sits, Mercury says. Methods differ by engine, so use the table and your manual. For four-strokes and conventional two-strokes, Mercury says to fog while the motor is still warm: remove the spark plugs and spray fogging oil into each cylinder, following the directions on the can. Pull the kill-switch lanyard first and keep the plug leads away from the open holes. For DFI two-strokes such as the OptiMax, Mercury says to put one ounce of DFI outboard oil into each cylinder through the spark plug hole instead; use the oil and amount your model's manual gives.
Change the gear lube
Mercury gives every 100 hours or once a season. With the gearcase cool, remove the vent screw and the drain screw and let the old lube drain into a pan. Pump new lube of the type your manual names in through the bottom hole until it weeps from the vent. Yamaha says to wait five minutes for air to escape, then pump again until it shows at the vent. Fit new gaskets on both screws and tighten them to the torque in your manual.
Check the old gear lube
Water in the gear lube can freeze and crack the gearcase, according to Mercury, so look at the old lube as it drains. Milky or separated lube means water. Yamaha also says to check the magnetic drain screws for large metal particles. Either one is a reason to have the lower unit inspected before freezing weather. Clean-looking lube is no guarantee, so keep to the change interval.
Replace the fuel filter
Mercury and Yamaha both include a new fuel filter in winterizing, and Yamaha's procedure replaces the fuel/water separating filter mounted in the boat. Work outdoors with nothing nearby that can spark, catch the fuel in a container and dispose of it properly.
Drain the cooling water
After the last run, tilt the motor all the way down so trapped water drains out, as Mercury advises, and follow any extra drain steps in your manual. Mercury warns that water left in the cooling system can freeze, expand and crack parts.
Disconnect and charge the battery
Mercury says never to leave a battery connected in a stored boat. Turn off every load, then remove the negative cable first (and reconnect it last in spring). Charge the battery fully and have it load tested (Yamaha), in a ventilated spot with a charger made for its type, and never charge a frozen or damaged battery. Keep it on a maintainer or check it monthly. Yamaha suggests storing it indoors somewhere cool and dry.
Grease and protect
Grease every fitting with the grease your manual names, which Yamaha says helps force out any water sitting there. With the battery disconnected and the lanyard out, remove the prop wearing gloves, grease the prop shaft and refit the prop to the torque in your manual. Mercury's checklist adds a corrosion barrier spray and a check of the anodes and the trim fluid. Spray only the surfaces the product's label names.
Store the motor
Use a breathable cover. If the motor stays outside, Yamaha says to trim it fully down, or to seal a plastic bag over the lower unit only once it is completely dry inside.
What each engine maker says about fuel and fogging
The two steps where the makers differ. Your owner's manual is the final word for your model.
| Maker | Fuel tank in storage | Fogging |
|---|---|---|
| Mercury | About 95 percent full for an older vented tank, leaving room for the fuel to expand. Newer non-vented tanks do not need to be filled. | Four-strokes and conventional two-strokes: fogging oil into each cylinder. DFI two-strokes: one ounce of DFI oil per cylinder. |
| Yamaha | 7/8 full, to limit condensation. Never plug or cap the tank vent. | Yamalube EFI fogging oil for most modern fuel-injected four-strokes; Stor-Rite fogging oil for two-strokes and carbureted motors. |
| Honda | As full as possible with fresh fuel, out of direct sunlight. | See the Storage section of your model's owner's manual. |
| Suzuki | No fill level given. Add stabilizer at the label rate, then run about five minutes at 1,500 rpm in neutral to spread it. | Differs by model. Follow the Storage section of your owner's manual. |
| Evinrude E-TEC | See the Storage/Winterization section of your operator's guide. | A built-in winterization mode fogs the engine itself. The steps are in the operator's guide. |
| Other makers | See your owner's manual. | See your owner's manual. |
How much fuel stabilizer per gallon
Use the rate on the label of the product you buy. The rates differ by product:
- STA-BIL 360 Marine: 1 ounce treats up to 10 gallons. Added to fresh fuel, one dose stabilizes it for up to 12 months, according to Gold Eagle.
- Mercury Quickstor: 1 ounce per 5 gallons.
- Star Tron Enzyme Fuel Treatment, concentrated formula: 1 ounce per 8 gallons for the first dose, then 1 ounce per 16 gallons at each refill, according to the label.
Winterize boat checklist
- Fresh fuel, stabilized at the label rate, tank at your maker's level.
- Motor run about 10 minutes outdoors, on muffs or in the water, water on first.
- Engine oil and filter changed (four-stroke).
- Engine fogged by your maker's method.
- Gear lube changed with new gaskets, old lube checked for water and metal.
- Fuel filter replaced.
- Motor tilted all the way down to drain the cooling water.
- Battery disconnected (negative first), charged and on a maintainer.
- Fittings greased, prop shaft greased, corrosion spray on.
- Motor covered, trimmed down if it stays outside.
Common questions
Mercury fogs its four-strokes through the spark plug holes, and Yamaha names an EFI fogging oil for most modern fuel-injected four-strokes. Suzuki's step differs by model, and Evinrude E-TEC motors fog themselves in a winterization mode. Follow the manual for your model.
It depends on the maker and the tank. Yamaha says 7/8 full and Honda as full as possible. Mercury says to fill an older vented tank to about 95 percent and that newer non-vented tanks do not need filling.
Mercury and Yamaha both give about 10 minutes, long enough for treated fuel to reach the whole fuel system.
It depends on the product. STA-BIL 360 Marine is 1 ounce per 10 gallons, Mercury Quickstor is 1 ounce per 5 gallons, and Star Tron concentrate is 1 ounce per 8 gallons for the first dose. Read the label of the bottle you use.
Milky gear lube has water in it. Mercury warns that water in the gear lube can freeze and crack the gearcase, so have the lower unit checked before freezing weather.
Yes. Fuel still goes stale and batteries still run down in storage, and water left in the motor can freeze in an unheated garage.
Sources
Mercury Marine's winterizing guide, seven winterizing mistakes and fuel stabilizer tip; Yamaha's extended storage guide and four-cylinder winterizing walkthrough; Honda Marine's fuel recommendations; Gold Eagle's STA-BIL 360 Marine page; Evinrude's owner FAQ; and the Star Tron and Suzuki directions as printed on the label and in the owner's manual.