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Still Have 1/3 of a Tank – How Do I Winterize the Motor?


Scott Hanley asked:

I am a novice first year owner living in Portland, Oregon. I have a 2002 21 foot used runabout with a standard 6 cylinder 350 Chevy IO engine. How do I winterize for storage for an outside carport and what can I do about the gas (approximately 1/3 tank) so it can be used 6 months from now without effecting the engine. (the “old gas” problem)? As far as I am aware, there is no drain for the tank.

The winter temperature in Portland will invariably freeze to 20-25 degrees for a couple of days..but that is about as cold as it gets.

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Welcome to the wonderful world of boating. I trust that your first year was a lot of fun.

The principals for winterizing are the same for most marine inboard motors and stern drives, however the details can differ, depending on manufacturer and type of engine. The first thing I would suggest is that you get a manual for the motor and stern drive on your boat and follow the manufacturers detailed instructions. Both OEM and aftermarket manuals are available. This will point out where the drain cocks and lubrication points are, plus give you torque specifications for retightening bolts you may loosen or remove and other information you will need if you are a DIY.

Start by adding a fuel stabilizer to the fuel tank to prevent break down and varnish build up, and top it up with fresh fuel. Topping up the tank will help prevent condensation from forming which could add water to the fuel. Do this before fogging your engine so that some of the stabilized fuel gets into the carburetor. It will help eliminate varnish build up in your carburetor over the winter. Onboard tanks do not have drains for safety reasons.

Next, run your motor to bring it to operating temperature (make sure that you hook up muffs and a garden hose to the water intake on the drive to prevent damage from overheating). Drain your engine oil and replace the oil and oil filter with the grade and type recommended by the manufacturer. Run the engine again and squirt fogging oil into the carburetor until the engine stalls and then turn it off.

I always remove the sparkplugs on my engines and squirt a few ounces of motor oil into each cylinder head and then replace the plugs. It’s a good habit to disconnect the battery while working on the motor and then reconnect after. Be sure not to mix up the ignition wires. Label them if necessary. Then disconnect the lead from the coil to the distributor and crank the engine for 10 or 15 seconds to make sure that the cylinder walls and rings are well coated. I do this to be doubly sure that rust will not form in the walls or rings. If this occurs, you can crack a ring when you try to re-start the engine next spring or the engine may be seized. The fogging oil is supposed to coat everything, but …

Clean the flame arrestor screen in Varsol, dip or coat it in oil and replace it.

Open the drain stop cocks, or remove them completely, and drain out the water. This is a good time to clean out any sand, mud or debris in the drain area. Replace and close the stop cocks.

Remove the thermostat housing and pour plumbers antifreeze (proper temperature range) into the engine, while cranking it. Make sure that the distributor wire is disconnected. Do this until the antifreeze starts to spit out the exhaust. Reinstall the thermostat and intake hose. (Do not reinstall the thermostat upside down). You will need a new gasket. Be sure it’s the right one. In some cases you can use an automotive type in other cases you can’t. Some have a special metal grommet to allow continuous grounding, without which your temperature sensor will not work. Best to use OEM or specific aftermarket gasket available from your local engine dealer. Marine Dealers have the luxury of submerging your lower unit in a drum of antifreeze and pumping it through to the exhaust. There are also kits available that allow you to pump the antifreeze through the water intake muffs into the engine, until it comes out the exhaust. Don’t skimp on the antifreeze, it’s cheaper than replacing your motor. If you pump through the water intake, you will not have to remove the thermostat housing.

This is a good time to replace the thermostat if you were having any over heating problems last summer or if it is starting to get corroded and also a good time to check all the hoses for brittleness, cracks, or if they are getting soft and spongy. Replace any hoses that need it. If in doubt, replace. It’s much easier now than in the middle of the lake, during a storm, without a spare onboard. Marine hoses should be double clamped. Also, check the wiring and connections and replace any that require it.

Make sure that your drives are down to allow for maximum water drainage. Change the oil in the drive lower unit and grease all the nipples around the gimble housing and trim rams. Remove the water intake grills and check for any obstruction and clean out if necessary. Clean any fouling on the drive and prop with Algex. If there is any pitting on the drive or if the paint has flaked off, sand it down and spray paint it with drive paint recommended by the manufacturer. Check the sacrificial zinks and replace if they are worn, pitted or broken. Remove the propeller and grease the shaft with high pressure waterproof grease. I suggest the grease recommended by the engine manufacturer. Store the prop at home so that it does not go missing over the winter. Winter is an excellent time to send the prop in for repairs if required. Everyone is too busy in the spring.

Lubricate the steering and control cables and the mechanical linkage on the carburetor. If there is any rust on the motor, scrape or sand it down and touch it up with engine enamel. You can use Boat Clean Plus to remove oil, grease and dirt from the motor. Marine engines should always be kept pristine so that you can easily notice any obvious problems or leaks when the boat is in use.

Loosen the bolt supporting the alternator to take the pressure off the drive belt. This will prevent the belt from getting a set and making clunking noises next spring

Add some motor oil to a rag and wipe down your engine to prevent rust and corrosion. While doing this, do a visual inspection for any loose or missing bolts or screws and anything else that looks like it needs attention.

Remove your battery and store it at home on a piece of wood. Check the fluid levels and top up with distilled water, to make sure the plates are covered . Do not leave it on the ground or on concrete as it could discharge. Use a battery charger to put a trickle charge on the battery about once a month to keep it healthy during the winter. If you have a volt meter or hydrometer, you can check your battery’s condition during the winter.

When you store your boat, remove the rear drain plug and store the boat bow high with the drive down. I always put the drain plug in a small plastic bag and tie it to the ignition key. That way it doesn’t get lost and it reminds me to re-install the plug before launching the boat. It helps stop that sinking feeling if you know what I mean.

I think I’ve covered all the bases. I suggest that you download the De-Commissioning Check List in the forum and modify it to include all your engine winterizing requirements. That way you won’t forget anything. It will also give you a good guideline for winterizing the rest of your boat. Remember, the more you can do in the fall and over the winter, the less you will have to do in the spring when you are in a rush to get your boat in the water for that first nice day.

Thanks for your question,

Captain Aurora

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