Winterizing a 2-Stroke Outboard Motor

Regardless of the season, you should winterize your outboard anytime it isn't going to be used for more than a month. 

You don't have to wait for snowflakes to fall to winterize an outboard. The sooner you get it winterized, the sooner you'll prevent it from being damaged by corrosion. Follow this walkthrough for the winterization process of a 2-stroke outboard motor, and watch the video above for additional guidance. 

Tools and Parts - Two-Stroke Outboard Winterization


Mercury outboard corrosion guard

Mercury storage seal fogging oil


Make sure you get the correct weight gear oil for your outboard. Your user's manual will tell you the gear oil the manufacturer recommends.

Winterizing Mercury 2-stroke outboard parts list

NOTE: We winterized a Mercury Tracker 25HP motor, but the process is the same or similar for all outboard makes and models.

Winterizing a 2-Stroke Outboard: Lower Unit Oil Change

Mercury recommends the gearcase lube be changed every 100 hours or once per year. However, you should do it regardless of how long it's been before storing your outboard, because harmful contaminants in the used oil can corrode the inside of the lower unit.

Changing the Gearcase Lube

Step 1. Remove the overflow screw and put a container under the drain screw to catch the old oil.

Mercury 2-stroke outboard gearcase oil change

Step 2. Remove the drain screw and washer, and let the oil fully drain. 

Step 3. Attach a gear lube pump to the drain hole and pump new gear oil into the gearcase until it reaches the vent hole. 

Step 4. Reinstall the vent screw, remove the gear lube pump, and reinstall the drain screw and washer. Wipe away any excess oil from around the vent and drain screws.

Winterizing a 2-Stroke Outboard: Fuel System

When left standing for weeks or months, fuel begins to oxidize and go stale, and the methanol attracts water molecules. 

Fuel stabilizer stops fuel from breaking down and oxidizing, and absorbs any water molecules attracted by the methanol.

Step 1. Add fuel stabilizer to your outboard's fuel system.

NOTE: Follow the recommendations on the fuel stabilizer's packaging to avoid over- or under-saturation.

Step 2. Run your outboard for a few minutes so the engine draws stabilized fuel into the fuel lines and the fuel system. Then, disconnect the fuel supply and continue to run the motor until it's just about to dry (when the motor begins to splutter).

Step 3. As the engine begins to splutter, spray fogging oil directly into the carburetor's throat.

Winterizing a 2-Stroke Outboard: Cylinders

The metal surfaces within the powerhead's cylinders need to be protected against corrosion. Spraying fogging oil into the cylinders will provide a coating over them that's effective against condensation and corrosion.

Winterizing Mercury 2-Stroke Outboard

Step 1. Remove the spark plugs, and spray fogging oil into each cylinder for 4-5 seconds.

Step 2. Gently pull the starter cord to rotate the engine a couple of times so the fogging oil gets spread all over the inside of the cylinders.

Step 3. Install new spark plugs, and torque them to the manufacturer's specs. 

PRO TIP: If you don't have a torque wrench, hand-tighten the plugs, then give them an additional 90-degree turn.

Winterizing a 2-Stroke Outboard: Powerhead

Now that the inside of the powerhead is protected against corrosion, you'll need to do the same to the outside of the engine. Spraying the powerhead with corrosion guard adds a light oily coating that protects all the external metal parts from corrosion.

Winterizing a Mercury Outboard corrosion guard

Step 1. Give the engine a light spraying of corrosion guard. Pay attention to any metal parts that aren't painted, such as linkages.

NOTE: Don't spray corrosion guard on any anodes or zincs, and clean them off immediately if you do.

Winterizing a 2-Stroke Outboard: Battery

While the battery isn't actually part of the outboard, it needs to go through charging and discharging cycles to remain healthy. A battery that's left idle for months will deteriorate to the point it can't be charged again.


DelTran Battery Tender Plus

Mercury QuickStor fuel stabilizer


Step 1. Remove the battery from the boat, and clean and coat the terminals with a smear of dielectric grease.

Step 2. Attach a Battery Tender to the battery and leave it on a level surface. The battery tender will keep the battery's power level optimized for months, and ensure it'll be in peak health when you're ready to take your outboard out of storage.

Got a 4-stroke outboard instead of a 2-stroke? As mentioned before, the winterization process for an outboard is essentially the same or similar for all outboards, but the video above is specific to 4-stroke engines. Watch the video above to see how to winterize a 4-stroke Mercury outboard. 



Commercial Discounts

Special discounts for companies in the marine industry


Government Sales

Discounts for federal and most state and municipal agencies