How to Winterize an Outboard Motor: Complete Fall Checklist

How to winterize an outboard motor comes down to five things in order: flush the salt out, stabilize and run the fuel, fog the cylinders, change the gear oil and read it, and store the engine vertical so the cooling passages drain. Everything else on the list, the impeller, the seals, the grease, is a decision you make while the motor is already apart. Here is the fall checklist we run on customer engines, with the numbers, and the parts that get replaced while the lower unit is off.

Step 1: flush, then stabilize and run the fuel

On muffs or a flush port, run fresh water through the engine at idle for 5 to 10 minutes, until the telltale runs steady and cool. Residual salt crystallizes over winter and is what plugs a telltale in April. If you flush from a dock, a Flushmaster Outboard Motor Flusher Cradle on a piling holds the Flushmaster flusher where you can hook up without leaning over the transom.

While it flushes, treat the fuel. Add stabilizer at the dose on the bottle, then run the engine another 10 minutes so treated fuel reaches the carburetor bowls or the vapor separator and injectors. Untreated ethanol fuel can start to degrade in as little as 30 days, and a carb full of it in October is a gummed jet in March.

Step 2: fog the cylinders

Fogging oil coats the cylinder walls, rings and bearings so they do not flash-rust in storage. On a carbureted two-stroke, hold a fast idle and spray fogging oil into each carb throat until the engine smokes heavily and stalls. On a Johnson or Evinrude with a primer solenoid, the Sierra 18-0871-1 Service Valve W/ O-Ring threads into the primer system and pushes fogging oil or engine tuner straight through it without pulling the air box; it fits all Johnson and Evinrude engines with a primer valve except the 1993 9.9 and 15 HP.

Then, on every outboard, pull the spark plugs, spray fogging oil into each cylinder for about 3 seconds, bump the starter with the kill lanyard pulled for a couple of revolutions, and reinstall the plugs. On a four-stroke the plug holes are the whole fogging step; do not spray into an EFI throttle body unless your manual says to.

Step 3: gear oil, and what it tells you

Trim the motor vertical, put a pan under the skeg, pull the lower drain plug and then the upper vent, and watch what comes out.

Refill from the bottom plug until lube runs clean out of the top vent; vent screw in first, then the bottom plug, new washers on both. A 9.9 or 15 HP Johnson or Evinrude that shows milky oil gets the Sierra 18-2656 Johnson/Evinrude Lower Unit Seal Kit, which covers the oil seals and the drain and fill plug washers in one kit. Milky gear oil is not a spring problem; a hard freeze splits the housing.

Step 4: the impeller decision

The water pump impeller is a rubber vane wheel that hardens and takes a set, under the lower unit you already have half off. Replace it every 2 to 3 seasons or about 300 hours, or now if the telltale weakened over the summer or the engine ever overheated. Fall beats spring for this: find a stuck driveshaft in October and you have months to sort it, not the week before opening day.

A Mercury 30 to 70 HP takes the Sierra 18-3007 Mercury 30-70HP Water Pump Impeller; Johnson and Evinrude engines that used the OMC 5001593 impeller take the Sierra 18-3059 Johnson/Evinrude Water Pump Impeller, key included. Grease the driveshaft splines lightly and keep grease off the top of the shaft so it cannot hydraulically lock the crank.

Step 5: grease, anodes and the prop

Pull the propeller. Behind it, wrapped on the shaft, is the fishing line that cuts the prop shaft seal and causes next year's milky gear oil; clear it. Grease the splines, reinstall the prop with a new cotter pin, and hit every fitting: tilt tube, steering, swivel bracket. Replace any anode more than half gone. This is also the moment for a bolt-on you have been putting off: a Davis Whale Tail XL Stabilizer mounts to the anti-ventilation plate, and drilling that plate is a job for a motor on a trailer in October, not a boat at the ramp in May.

Step 6: store it vertical

Trim the motor fully down so the leg is vertical and every cooling passage drains. Water expands about 9% when it freezes, and an outboard stored tilted up with water trapped in the leg or exhaust housing cracks; it is the most expensive winterizing mistake and costs nothing to avoid. Pull the battery, charge it, store it above freezing. Touch up chipped paint on the lower unit, and leave the cowl vented under shrink wrap so the powerhead does not sweat.

How to winterize an outboard motor: the checklist

1. Flush 5 to 10 minutes.
2. Stabilize the fuel, run 10 minutes.
3. Fog the carbs or primer system, then the cylinders.
4. Drain gear oil vertical; reseal if milky; refill from the bottom.
5. Impeller at 2 to 3 seasons or 300 hours.
6. Pull the prop, clear the line, grease, check anodes.
7. Store vertical, battery out, cowl vented.

PPE is nitrile gloves and eye protection; the drained fuel and carb bowl contents go in a sealed can, not the driveway.

Frequently asked questions

What You Need For This Job

• Sierra 18-3007 Mercury 30-70HP Water Pump Impeller: impeller for Mercury 30 to 70 HP outboards
• Sierra 18-3059 Johnson/Evinrude Water Pump Impeller: impeller with key for Johnson and Evinrude engines using OMC 5001593
• Sierra 18-2656 Johnson/Evinrude Lower Unit Seal Kit: every gearcase seal plus drain and fill washers for the 9.9 and 15 HP
• Sierra 18-0871-1 Service Valve W/ O-Ring: fogging oil through the Johnson and Evinrude primer system without pulling the air box
• Davis Whale Tail XL Stabilizer: the bolt-on to do while the motor is on the trailer