--- ## Quick Answer You can winterize your own Mercury outboard only after identifying the exact storage procedure in the operation and maintenance manual for its serial number. Fuel treatment, internal engine protection, flushing, gearcase service, and storage position vary...
Quick Answer
You can winterize your own Mercury outboard only after identifying the exact storage procedure in the operation and maintenance manual for its serial number. Fuel treatment, internal engine protection, flushing, gearcase service, and storage position vary by engine family. Do not assume every FourStroke should be fogged through the intake, and never run the motor without a cooling-water supply. If the procedure or inspection is outside your ability, submit the motor details at hbw.wiki/service.
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variant: inline
heading: Keep the fall storage work together
body: This one-page checklist covers appointment prep, fuel and engine work, onboard systems and the record to keep. The storage section in your serial-number manual decides the procedure.
primaryLabel: Download fall checklist (PDF)
primaryHref: /downloads/fall-storage-winterization-checklist-hbw.pdf
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For professional winterization and winter boat storage in the Kawarthas: hbw.wiki/service.
Safe fall checklist
Winterizing your Mercury? Start with the exact manual
The order and supplies change by engine. Use the serial-number manual before opening the cowl or draining a fluid.
Identify
?Do you have the operation and maintenance manual for the exact engine?
💡Confirm the serial number, engine family, year, and storage section. A generic FourStroke checklist is not enough.
Fuel
?Does the fuel meet Mercury's specification, and have you followed the model's storage guidance?
💡Use fresh fuel, the stabilizer concentration Mercury specifies when applicable, and the run time stated in the manual.
Gearcase
?Is the lubricant due, and did it show water or metal?
💡Milky lubricant, metal, damaged seals, or uncertain fill procedure are reasons to stop and request service.
Engine protection
?Are you following the exact internal-protection and flushing method?
💡Some procedures differ from generic fogging advice. Keep cooling water supplied whenever the engine runs.
Battery and position
?Is the battery disconnected and maintained, and is the motor stored in the position the manual specifies?
💡A healthy battery may remain aboard only if fully charged, disconnected, secured, and permitted by the approved storage plan. The model/serial manual and approved storage plan control. The exact engine position must allow proper drainage.
🔧Need the model-specific scope?
Submit the serial number, engine hours, and service history at hbw.wiki/service. HBW is closed December 1 through April 1.
DIY Mercury Outboard Winterization: What to Do, What to Skip, and When to Call a Dealer
Ontario's boating season has a hard stop. Fuel condition, water-contaminated gear lubricant, battery state, corrosion protection, and the motor's drainage position all matter during a long freeze.
Winterization is storage preparation, not one universal fogging recipe. The exact Mercury procedure depends on the engine family and model year.
This guide covers what DIY winterization actually involves, which steps are realistic for most owners, which ones are easy to get wrong, and when it makes more sense to bring the motor to a dealer.
Late-season winterizations, from August through November, are one of the busiest stretches of our service year at HBW. The May and June diagnostic work that follows every spring includes a consistent number of motors that weren't winterized correctly, DIY or otherwise.
Who Should DIY and Who Shouldn't
DIY is realistic if:
- You're comfortable working around a motor and have done basic maintenance before
- You have a smaller motor (under 60 HP is more manageable for a first DIY attempt)
- You have storage access with space to work around the motor
- You can run the motor briefly at home (with flush muffs or a water supply)
- You have the right supplies and aren't guessing at quantities or procedures
Consider professional service if:
- You've never done this before and aren't confident with mechanical work
- You have a larger, more complex motor (especially V6, V8, or Verado)
- You're not sure you can clear the cooling system properly
- You're rushed and likely to skip or hurry steps
- The motor is stored somewhere you can't access it easily for prep
For engine repairs, we only service Mercury and MerCruiser.
What You Need Before Starting
Pick these up at a Canadian Tire, marine store, or from your dealer's parts counter before the last day on the water:
- The operation and maintenance manual for the exact serial number
- Fuel stabilizer only if the storage procedure calls for it
- The gearcase lubricant and quantity specified for the model
- New drain-plug seals when the manual calls for replacement
- The exact tools listed for the tasks you are performing
- Mercury-specified lubricant for the applicable grease points
- A bucket and rags
- The approved flushing connection or cooling-water supply for the engine
If the procedure requires the engine to run, use the water-supply method and flow Mercury specifies. Never run or dry-crank an outboard without cooling water.
The Winterization Sequence
Watch Mercury's official winterization checklist:
How To Winterize Your Outboard | Winterization Checklist (Mercury Marine)
Mercury demonstrates this checklist on one outboard. Use the storage procedure in the operation and maintenance manual for your exact engine and serial number.
Do these in order. Don't skip steps. If you're not sure what you're looking at at any point, stop and bring the motor in.
Step 1: Stabilize the Fuel
Do this before your last run of the season, not after.
- Start with fresh fuel that meets the manual's specification.
- Add the stabilizer Mercury specifies, at the product's stated concentration, when the storage procedure calls for it.
- Circulate treated fuel for the time and by the method in the exact engine manual.
Ethanol note: If you're running pump gas with ethanol (E10), this step matters more. Ethanol absorbs water and can cause phase separation in stored fuel. Ethanol-free fuel is available at HBW on-site, filling up with it at the end of season simplifies this step considerably.
Do not use one generic full-tank or empty-tank rule for every portable tank, built-in tank, carbureted motor, and EFI system. Follow the storage guidance for the boat's actual fuel system.
Step 2: Flush the Cooling System
Use the flushing connection, engine state, water flow, and duration stated in the exact manual. Some flushing attachments are used with the engine off; other procedures require a running engine and a continuous water supply. Do not assume generic muffs and a five-minute idle are correct for every model.
After shutdown, store the motor in the position Mercury specifies so water can drain.
Step 3: Follow the Model-Specific Internal Protection Procedure
Do not spray fogging oil into the intake simply because a generic checklist says to. Mercury storage procedures vary across current FourStrokes, older carbureted two-strokes, direct-injected engines, ProKicker, Verado, and other families.
Use only the product, access point, engine state, and sequence in the exact manual. If the procedure requires removing spark plugs, opening the intake, disabling fuel or ignition, or running a special mixture and you are not confident, stop and request service.
Step 4: Drain and Refill the Gearcase
The lower unit gearcase contains gear lube that absorbs water through the seals over a season of use. If you leave that water-contaminated lube in over winter, it can freeze, expand, and damage the gear case or seals.
- Remove both drain/fill plugs from the gearcase, the lower one first, then the upper one.
- Let the old gear lube drain completely into a container.
- Inspect what drains. Milky or foamy gear lube indicates water intrusion, this is a sign you need seal inspection before assuming the gearcase is healthy.
- Using a gear lube pump, fill from the bottom hole until lube comes out the top hole with no air bubbles.
- Install the top plug first, then the bottom plug. Replace the gaskets, they're cheap and the small cost of a new gasket beats a gear lube leak.
Use Mercury-branded gear lube appropriate for your motor. The spec is in your owner's manual.
Step 5: Lubricate All Grease Points
Every Mercury has grease fittings on the steering and tilt/trim pivot points. These need marine grease before storage. Dry or under-greased pivot points seize over winter and result in stiff, damaged components in spring.
Follow the lubrication diagram in your owner's manual. Common points:
- Tilt/trim tube and pivot
- Steering cable end (if applicable)
- Swivel bracket
- Propeller shaft, using the lubricant Mercury specifies
- Any other fittings shown in your manual
Don't skip the prop shaft. A prop that corrodes onto the shaft over winter is a spring headache.
Step 6: Disconnect and Maintain the Battery
The battery can remain in the boat if it is disconnected and maintained according to the battery maker's instructions. Use a compatible smart maintainer only where the storage setup and charger instructions allow it. Clean and protect the terminals, and load-test the battery before launch.
Step 7: Final Check, Water Drain
Before putting the cover on:
- Move the motor to the storage position specified in its manual
- Confirm drainage openings are not obstructed
- Do not leave the motor in a position that can trap water
Step 8: Cover and Store
Cover the motor with a vented motor cover or cowling cover. A non-vented plastic wrap traps condensation. The motor needs to breathe slightly while in storage.
If the boat goes into covered indoor storage, this is less critical. Outdoor or unheated storage needs proper covering.
What Gets Missed Most Often
Based on what we see in spring diagnostics at HBW:
- Using a generic procedure for the wrong engine. The correct internal-protection, flushing, and storage steps vary by model.
- Running without cooling water. Even a short dry run can damage the water-pump impeller.
- Milky gear lube ignored. If gear lube came out milky and the owner just refilled without addressing the seal leak, the new lube goes milky again by spring.
- Battery left connected. Parasitic draw can leave a discharged or damaged battery by spring.
- Stabilizer added but motor not run afterward. The stabilizer never reached the injectors or carbs, so they saw unstabilized fuel all winter.
When to Let a Dealer Do It
The guide above is a decision framework, not a substitute for the serial-number manual. If you find water or metal in the gearcase lubricant, damaged seals, alarms, fuel contamination, corrosion, or a procedure you cannot complete exactly, stop and request professional service.
If you want professional winterization: hbw.wiki/service. The shop knows these motors.
Reviewed by
Reviewed by the Harris Boat Works service team. HBW handles Mercury and MerCruiser service from Gores Landing on Rice Lake. For engine repairs, we only service Mercury and MerCruiser. About Harris Boat Works.
Want it done right without the Saturday morning?
Request professional winterization at hbw.wiki/service. Harris Boat Works, Gores Landing, Mercury Premier dealer. Mercury dealer since 1965, family marina on Rice Lake since 1947.
Phone: 905-342-2153
