Winterizing Must Do's

By Bob Adriance

If your boat is on a trailer, don't procrastinate; here's what you need to do before the cold weather sets in.

The BoatUS Marine Insurance claim files show that a boat on a trailer is more likely to be damaged in an early freeze than a boat in the water. Here's how to avoid that.

Top Off Fuel Tanks

Tanks should be full (but leave some room for the gas to expand), which minimizes explosive fumes and helps prevent phase separation if the gasoline contains ethanol. Add stabilizer to keep the gasoline from losing its kick.


If you can do it, charge them fully, remove from the boat, and store in a warm place. Coat the posts and terminals with WD-40 to keep corrosion from interrupting a connection.

Outboards and I/Os

Look at your owner's manual for specific winterizing instructions. With four-stroke outboards and sterndrive inboards, you'll need to change the crankcase oil and filters. Before changing the oil, use a screw-on attachment or a muff to get cooling water to the lower unit so that you can run the engine and lower the oil's viscosity. Note: When you loosen the drain plug, watch for water or a creamy-colored liquid, which indicates a seal needs replacing. Sometimes, metal shavings can be seen, which also require professional attention. Various devices for changing oil as well as muffs are available in the West Marine catalog.

To winterize the raw-water-cooling system, use the garden hose to bring the engine back up to operating temperatures. Shut the engine off and connect the hose to a bucket of nontoxic antifreeze (a handy kit for winterizing lower units is available at West Marine). Start the engine, which will pull the antifreeze through the cooling system until you see it come out the exhaust. Running the engine before you add antifreeze opens the thermostat so that antifreeze will get into all the cooling passages. As an alternative, you can also remove the thermostat. Just before the bucket of antifreeze is empty, squirt a fogging spray into the carburetor (if the engine has one), which should stall the engine. If not, turn off the ignition. To deter theft, smaller outboards are safer in your garage.


Change the oil and filters. The method of winterizing the cooling system is similar to I/Os but is done by disconnecting the intake hose and placing it in a bucket of nontoxic antifreeze. The transmission fluid should be drained and new gear oil added.

Using Biminis as Winter Storage Covers

There seems to be a common misconception that a cover that protects the crew from glaring sun will also protect the boat from freezing rain and snow. Biminis tend to get ripped apart or, more likely, age prematurely from the effects of winter weather while doing absolutely nothing to protect the boat. A bona fide winter cover, on the other hand, is terrific protection. Biminis should be stored inside the boat over the winter or, better yet, taken home for cleaning and safekeeping.

Remove the Removables

If electronics can be removed, do so. If you keep registration information onboard, take it inside for the winter. Remove cushions, too, to prevent mildew buildup. If this is not possible, prop the cushions up so air can circulate on both top and bottom. Remove life jackets, anchor lines, and dock lines for the same reason. Open any lockers and bilge covers, and hang a mildew-control bag.

Inspect the Inspectables

This is the right time to take a look at expiration dates of flares as well as the charging status of the fire extinguisher. It is always better to discover out-of-date equipment when at home on land than when you need them or when the Coast Guard has just come alongside while on the water, asking to do an inspection. While you are in this mode, bring the first aid kit inside and replace bandages that may have become wet or medical supplies that have expired. 

This article was published in Fall 2012 issue of Trailering Magazine.

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