How Do I Winterize My Mercury Outboard?

How Do I Winterize My Mercury Outboard?

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Winterizing your Mercury outboard is the last step before sending the motor into hibernation at the end of the season. As a precursor to the winterizing process, mixing fuel stabilizer into the last tank of fuel for the final excursion of the season allows the fuel stabilizer to circulate throughout the motor, coating the various fuel system surfaces with the stabilizer. After that, it's all about the motor and the care needed to see it through the long winter before the next boating season begins.

Items you will need

  • Marine grease

  • Garden hose

  • Flushing attachment

  • Fogging oil

  • New spark plugs

  • Plug wrench

  • Fuel filter replacement element

  • Oil change pan

  • Screwdriver

  • Gear case lubricant

  • Moisture-excluding spray lubricant

Remove the propeller. Take the propeller to a certified propeller technician for repair of any damage. Apply a coating of heavy marine grease to the propeller shaft.

Attach a garden hose to the Mercury flushing attachment. Slip the flushing attachment's "ear muffs" over the two water inlets on the motor's lower unit---the extension that comes down from the engine to the propeller. Turn the hose on full force.

Ensure the transmission is shifted into neutral. Start the motor and allow it idle in neutral for three to five minutes while water circulates and flows from the engine. Turn off the fuel shut off valve on your fuel line and spray fogging oil into the carburetor until the motor shuts down. Turn off the water and remove the flushing attachment. Remove each spark plug, spray fogging oil into the cylinder and put in new spark plugs.

Change the fuel filter, located in the fuel line near the carburetor, by unscrewing its two-part clear plastic housing, removing and replacing the filter element and screwing the two halves of the housing back together. Squeeze the fuel primer bulb until it's full of fuel and firm to the touch. Check the fuel filter for visible leaks.

Drain the gear case into an oil change pan by unscrewing the plug from the fill hole on the gear case, and the plugs from the front and rear plug vents just above the motor's skeg, on the right side of the motor. Retain the washers on the plugs. Lubricate the gear case by squeezing tubes of lubricant into the fill hole on the gear case until it comes out the front vent hole. Put the washer onto the front plug and screw the plug in place. Keep adding lubricant until it comes out the rear hole, then screw the plug into the rear hole.

Lightly dust the entire motor with a moisture-excluding spray lubricant. Store the motor upright on a motor stand.


  • Removing the propeller isn't optional. Every year, propeller strikes maim and kill boaters doing maintenance with the propeller in place.


  • Change the motor oil as part of the fitting out process at the beginning of the boating season.
  • The gear case plugs can be unscrewed with a common screwdriver.
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