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Winterizing your Sailboat

Winterizing can be complex and involves a lot of tasks, so here is a detailed checklist we use – it’s mainly based on West Marine’s checklist, with some other inputs.

The way we look at it, the more we do in the fall, the faster we get in the water in the spring.

Stabilize the FuelCheck your fuel-water separator for sediment and water and clean or replace the elements as needed.

Fill tank 95% full with clean diesel and add fuel stabilizer such as Biobor JF or Star Tron, recommended by Practical Sailor.

Run engine to distribute the stabilizer through the fuel system.

Change the Oil

Change the engine’s oil and replace the oil filter now, instead of waiting until spring, so you don’t leave the old dirty oil that could harm the engine over winter. Change the transmission oil too.

Run the engine up to operating temperature and change the oil while it’s warm to help drain any contaminants and gunk away with the oil.


Spray some oil into the inlet manifold. Then crank the engine over a few times (without starting it) to coat the cylinder walls with oil.

Lube all grease points on the engine and grease control cables.

Winterize the Cooling System

Some owners like to drain the entire system, but this must be thorough, as small pockets of water can crack important engine parts. We prefer to fill the cooling system with antifreeze, which is better for the engine and less likely to result in freeze damage.

Fill a five-gallon bucket with enough non-toxic antifreeze for your engine and related plumbing (at least two gallons, have more ready if needed). If the boat is in the water, close the intake seacock.

Remove the raw water intake hose from the seacock and insert the end into the antifreeze in the bucket.

Start the engine and run at idle until antifreeze comes out from the exhaust outlet for 30 seconds or more.

Secure the intake hose back on the seacock.

Check the Exhaust SystemBreak the exhaust loose from the water lift muffler or exhaust manifold and inspect for carbon buildup or corrosion. Take the raw water injection hose off the injection nipple and see if it has become blocked by debris or scale.
Inspect HosesCheck hoses for evidence of softness, bulging or cracking. Pay extra attention to the hot side of the exhaust and cooling systems. Check the hose clamps to be sure they are tight and look for corrosion.
Seal Engine OpeningsSeal all the openings that go into the engine to prevent the damp air from getting inside. Make caps out of plastic containers and tape to cover the air inlet, transmission and crankcase breathers and exhaust outlets. Remember to uncap them in the spring.
Engine MountsInspect the motor mounts and check their flexible rubber elements for softening caused by leaks of oil or diesel fuel.
Potable Water System

Drain water from all freshwater system lines and pumps.

Check impellers for wear and lubricate with Teflon®-based grease.

Inspect hoses for signs of softening, cracking, bulging, leaks or pinholes and replace, if necessary, before filling lines.

Fill all plumbing system lines with nontoxic antifreeze.

Before recommissioning, add water freshener/purifier tabs to tank to remove residual odors and condition newly added water.


Clean and drain bilge completely. Inspect and lubricate all seacocks.

If the boat is kept in the water, tighten the stuffing box to eliminate dripping and of course remember to loosen it in the spring.

Clean out refrigerator, ice box and freezer. Block door open and leave an open box of baking soda inside to absorb odors.

Remove cushions and curtains and store ashore.

Check and clean all storage compartments.

Secure all hatches and ports.

Place dehumidifying devices.

Check to make sure ventilators are operating properly.

Marine Sanitation Systems

Empty waste holding tank at an approved pumpout facility.

Rinse holding tank thoroughly to remove residual waste.

Pump antifreeze through bowl.

Lubricate gaskets and seacocks.

Check hoses for calcification and signs of wear. Replace if necessary.

Wash out vented loops.

Fill discharge and intake hoses with antifreeze.

Add antifreeze to holding tank to prevent freezing of residual waste.

GeneralTouch-up paint, remove rust, clean up grease.

A note on Antifreeze

There are two types of antifreeze.

  1. Common automotive antifreeze like Prestone is great for cars, but not good for marine diesel engines because its highly toxic.
  2. For marine applications we use the non-toxic variety which is usually made from propylene glycol in case it ends up in storm drains or the water.

Use the highest concentration available, which works down to -100° because there’s always some leftover residual water inside the engine that dilutes the antifreeze you put in.

West Marine have a great article on all aspects of Antifreeze, please click here to read.

Some owners remove the impeller from the raw water pump, lubricate it with petroleum jelly and put it back, leaving the cover screwed in place loosely, preventing the impeller sticking to the housing.

West marine also has a great article on this topic too: Impeller Replacement 101

To download this document a a pdf, please click here.

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