How to Winterize an Outboard Motor: Complete Step-by-Step Guide

Why Winterizing Your Outboard Matters

Skipping winterization is the #1 cause of costly spring repairs. Water left in your engine can freeze, crack the block, and destroy your lower unit. This guide shows you exactly how to protect your investment.

What You'll Need

• Fuel stabilizer (Sta-Bil or similar)
• Fogging oil
• Fresh lower unit gear oil
• Spark plug wrench
• Engine flush adapter or muffs
• Fresh water supply

Step 1: Add Fuel Stabilizer

Add the recommended amount of fuel stabilizer to a full tank of gas. Run the engine for 10-15 minutes to circulate the treated fuel through the entire system. This prevents ethanol-related fuel system damage over winter.

Step 2: Flush the Engine

Connect your flush muffs or adapter to a fresh water supply. Start the engine and run it at idle for 5-10 minutes. This removes salt, sand, and debris from the cooling system. Critical: Never run an outboard without water flowing through it.

Step 3: Fog the Engine

With the engine running (still on the hose), remove the air intake cover. Spray fogging oil directly into the carburetor(s) until the engine starts to stumble and smoke heavily. This coats all internal surfaces with protective oil.

Step 4: Change the Lower Unit Oil

Remove both the drain and vent plugs from the lower unit. Let all oil drain completely. Look for milky or gray oil - this indicates water intrusion and means your seals need attention. Refill from the bottom up until clean oil comes out the vent hole.

Step 5: Remove Spark Plugs and Fog Cylinders

Pull each spark plug and spray fogging oil directly into each cylinder. Turn the engine over by hand a few times to distribute the oil on the cylinder walls.

Step 6: Disconnect the Battery

Remove the negative terminal first, then the positive. Store the battery in a cool, dry place. Consider a trickle charger to maintain charge over winter.

Step 7: Final Checks

• Grease all fittings
• Touch up any scratched paint
• Cover the engine with a breathable cover (not plastic)
• Store in a dry location if possible

Spring De-Winterization Checklist

When spring arrives, reconnect the battery, install fresh spark plugs, check all fluid levels, and run the engine on muffs before your first trip. Your properly winterized outboard should start right up!

Need help? Our emergency checklist covers exactly what to check if your engine won't start after winter storage.