How to Winterize an Inboard & Outboard

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An inboard and outboard engine, or IO, is the type of larger boat engine that houses both an inboard motor and outboard mechanics to propel the boat. Like any recreational engine they require winterizing during months they won't be in use. Unlike land-locked RVs, these are constantly in water so you need to take special care to avoid cracking or freezing of the engine block during the cold winter months.

Fill the gas tank to full and add a can of gas stabilizer, depending on the amount needed for the number of gallons of gas you are treating.

Connect the flushing ears or muffs to the water inlets on the out drive. Normally, these take in the fresh water and circulate it to cool the engine, but when in dry dock, you need to use a water source. Never run the engine dry, as this will damage it. Place the hose in the sea cock of the water pump where the hose normally goes to the hull. If your boat engine is configured differently, be sure to connect the hose to the water intake on the water pump. Make sure the outboard portion of the motor (the propeller housing and shaft) are in the lowest position possible so all water will drain when you clear the system. Turn the engine on and let it run.

Remove the air cleaner from the carb and spray the fogging oil into the passages. This will coat the inside of these areas and keep moisture from penetrating the system. Disconnect the fuel line from the engine so the lines and delivery system will run dry. This will keep them from corroding when nothing is moving through them during the winter.

Turn the engine off or wait for it to run dry and stop from lack of fuel. Disconnect the water hose and remove the muffs from the intakes. Look for the petcock or drain to the water cooling system on the engine, and release the plug. Drain the system, replace the plug and fill it with antifreeze. If you are changing the oil as part of winterizing, now is the time to do that; otherwise, check the oil level and be sure it is completely full. Add antifreeze to the block until it doesn't accept any more. You can check by opening the drain slightly to be sure the system is full and there is no blockage.

Add a bit of antifreeze to the bilge area to avoid freezing of any standing water that may affect the engine. Disconnect the battery. It's a good idea to periodically charge the battery in the winter with a trickle charger if possible.


About the Author

Caprice Castano recently left the field of construction management to operate her own contracting business and spend time developing her writing career. Current projects include freelance writing for Internet publications and working on novel-length fiction.

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