Winterizing an I.O.

As the leaves begin to turn and the chorus of migrating waterfowl looms ever closer, thoughts turn from lakes and rivers to fields and woods. Before putting the boat away for the season, however, proper winterizing will ensure your rig is ready to go in the spring. There are three general areas that require attention, including the outboard motor and fuel system, boat, and trailer.

    • 1

      Use the power trim and tilt mechanism to lower the lower unit on the boat to the full down position. Water inside the lower unit will drain away.

    • 2

      Look for the drain plugs on the exhaust manifold and engine block. On in-line motors there is only one drain plug on the manifold and one on the block. On V-6 and V-8 engines, each side of the engine block has its own plug and each of the two manifolds has a plug.

    • 3

      Remove the drain plugs and let the water drain into the bilge. On newer I/O motors the drain plugs are plastic and can usually be turned by hand. On older motors, the drain plugs are brass, usually with a square or hexagonal head. Use an appropriately sized wrench to unscrew the plugs.

    • 4

      Replace the plugs once the water stops draining.

    • 5

      Remove the boat’s drain plug to drain the bilge.

    Fuel and Fogging

    • 6

      Fill the fuel tank to the top to lessen the possibility of condensation occurring inside the fuel tank over the winter.

    • 7

      Add Sta-bil or a similar fuel stabilizer to the tank according to label directions.

    • 8

      Spray fogging oil into the carburetor or the air-intake on fuel injected motors while the motor is being run and filling with antifreeze (see the “Add Antifreeze” section). This will coat the pistons and cylinder walls with oil to prevent rusting over the winter.

    Add Antifreeze

    • 9

      Affix a motor muff to the water intake slots on the boat’s lower unit, then attach a 6-foot length of garden hose to the motor muff. The male end of the hose will thread into the muff’s hose connection.

    • 10

      Put a large funnel into the other end of the garden hose and secure the funnel to the hose with a hose clamp.

    • 11

      Have a helper hold the funnel so you can pour antifreeze into it. If you don’t have a helper, rig up some sort of bracket to hold the funnel upright.

    • 12

      Fill the funnel and hose with antifreeze rated below the minimum winter temperatures for the area in which the boat will be stored. If the temperature for your area occasionally gets to zero, use antifreeze rated for at least -10 degrees.

    • 13

      Start the boat’s engine and let it idle.

    • 14

      Watch the level of antifreeze in the funnel. At first it will drain into the motor muff very slowly but once the motor warms up, with all the water drained from it, the thermostat will open and the antifreeze will quickly pump into the motor.

    • 15

      Pour antifreeze into the motor until all 4 gallons are used or until antifreeze begins to pump out of the motor’s discharge inside the propeller hub.

    • 16

      Shut off the motor.


  • Tips & Warnings


  • Although not necessary to prevent the motor from freeze damage, this is a great time to change the motor’s engine oil and lower unit oil so the boat will be ready for spring. It’s also a good idea to remove the battery, sonars or other electronics and store them inside over the winter.

  • Order Winterizing Kits Here