How to Winterize an Outboard Motor – Step-by-Step Guide

When boating season winds down, knowing how to winterize an outboard motor can save you costly repairs and ensure you’re ready to launch without issues next spring. Cold weather, moisture, and fuel degradation can damage your engine, but with proper maintenance, you can store your boat confidently for the winter months.

In this guide, we’ll break down every step, from draining water to treating the gas tank, so your outboard is protected until warmer days return.

Why Winterizing Your Outboard Matters

Whether you own a two-stroke or four stroke model, winterizing prevents corrosion, fuel breakdown, and internal engine damage. Many boat owners who skip this step find themselves dealing with seized parts, clogged filters, or cracked components after the freeze. A little preparation now means your engine will start smoothly and perform reliably when you hit the water again.

If you’ve ever wondered whether you should winterize an 115 outboard motor or a smaller engine, the answer is always yes. Even mild winters can cause moisture buildup and fuel problems if you store your boat improperly.

Step 1: Prepare Your Work Area and Tools

Before you begin, gather your supplies. You’ll need:

Fuel stabilizer
Engine oil and filter
Oil filter wrench
Gear lube
Spark plugs
Grease
Fogging oil
Fresh water source for flushing
Drain pan
Protective gloves

Always consult your owner’s manual before starting. Different outboards may have slightly different maintenance requirements, especially between a stroke outboard and a 4 stroke design.

Step 2: Flush the Engine with Fresh Water

Start the motor while it’s in a vertical position and attach a water source to the flushing port or muffs. Let it run for about 10 minutes to clear salt, sand, and debris from the cooling passages. This is critical for preventing mineral deposits and corrosion inside the engine.

While flushing, check for steady water flow from the tell-tale. If it’s weak, your water pump or impeller may need replacement before winter storage.

Step 3: Treat the Fuel System

Old fuel can form varnish and gum, clogging the fuel injectors or carburetor jets. To prevent this:

Add the recommended amount of fuel stabilizer to the gas tank.
Fill the tank to about 95% capacity to reduce condensation but leave room for expansion.
Run the engine for 10–15 minutes so the stabilizer circulates through the fuel system.

This will protect the fuel lines, injectors, and carburetors during storage. It’s a step you should never skip when learning how to winterize an outboard motor.

Step 4: Change the Engine Oil and Filter

Changing engine oil before storage removes acidic contaminants that could harm the engine’s internals.

Warm the motor slightly so the oil flows easily.
Remove the drain plug and let the oil empty into a pan.
Replace the oil filter using an oil filter wrench.
Refill with fresh, manufacturer-approved engine oil.

If your motor has an oil and filter change interval listed in the manual, winter is the perfect time to do it—this way, your engine starts next spring with clean lubrication.

Step 5: Drain and Replace Gearcase Lube

Water in your gear lube can freeze and crack the housing. Here’s how to avoid that:

Remove the lower drain plug, then the upper vent plug.
Let all gear lube drain completely.
Check the oil for a milky color—this indicates water intrusion, and you may need new seals.
Pump fresh gear lube from the bottom until it flows from the top vent, then reinstall the plugs.

Step 6: Fog the Engine for Corrosion Protection

Fogging coats the internal parts of the engine with a protective layer of oil to prevent rust during storage.

Remove the engine’s air intake cover.
Spray fogging oil into the air intake while the engine is running.
When the engine starts to sputter, spray more until it stalls.

This ensures the cylinders, pistons, and valves are protected.

Step 7: Grease Moving Parts

Lubricate all grease points listed in your manual, including steering linkages, throttle pivots, and tilt mechanisms. Grease creates a moisture barrier and keeps these parts moving smoothly.

Step 8: Remove and Inspect the Propeller

Taking off the propeller lets you check for fishing line wrapped around the shaft, which can damage seals. Clean and grease the shaft before reinstalling the prop or storing it separately.

Step 9: Disconnect and Store the Battery

Remove the battery from the boat and store it in a cool, dry place. Keep it charged over the winter by topping it up monthly with a trickle charger.

Step 10: Cover and Store Your Outboard Properly

If your motor stays on the boat, make sure it’s stored in a vertical position so water can drain from the exhaust housing. Cover the engine with a breathable motor cover to prevent dust and moisture buildup.

Some boat owners choose to remove the engine entirely and store it indoors, which offers the best protection.

Special Note on Larger Engines

If you’re wondering how to winterize an 115 outboard, the steps are essentially the same as for smaller models, but you’ll need to ensure you have enough stabilizer and oil capacity for the bigger engine.

The same applies if you want to winterize an 115 outboard motor—pay attention to torque specs, oil volumes, and the number of grease points, as these can differ from smaller units.

Common Mistakes to Avoid

Forgetting to run the engine after adding fuel stabilizer
Leaving the gas tank empty, which encourages condensation
Skipping the gear lube change
Storing the motor in a tilted position
Not checking for fishing line on the prop shaft

Závěrečné myšlenky

Taking the time to properly winterize an outboard is an investment in your boat’s longevity. By following these steps—flushing, stabilizing, changing oil and filter, lubricating moving parts, and storing the engine correctly—you’ll avoid costly repairs and ensure your outboards are ready when boating season returns.

Once spring arrives, you’ll simply reconnect your battery, check fluid levels, and enjoy a smooth first run. Proper winterizing isn’t just about protecting your engine—it’s about ensuring your next season starts trouble-free.

How to Winterize an Outboard Motor – Step-by-Step Maintenance Guide