How to Winterize a Pontoon Boat: Engine, Tubes, Furniture, Cover and Storage

Avalon and Harris both put cleaning first: the season's grime, algae and water spots come off far more easily now than in spring. Wash the tubes with a cleaner labeled safe for aluminum (never a harsh acid), scrub the deck, wipe down the furniture and vacuum the carpet, as Bennington suggests. Let everything dry completely before it gets covered.

Avalon says life jackets, skis, tubes, wakeboards, towels and fishing gear trap moisture and cause mildew, so take them off. Remove electronics you can unplug and take them home to protect them from cold, moisture and theft. Bennington stresses removing all food and drink, which is what draws mice in.

Avalon and Harris say to store the tank at least three-quarters full so there's less air space for condensation. Mercury goes further: fill to about 95% (leaving room for expansion), add a marine fuel stabilizer, and run the engine 10 to 15 minutes so treated fuel reaches the whole system. Run it on flush muffs or in the water. See the ethanol fuel care guide.

Mercury says used oil holds acids that attack internal parts during storage, so change the oil and filter on four-strokes before layup, and check or replace the gearcase lube. Water in the lower unit oil can freeze and crack the gearcase, so milky lube is a warning. The outboard oil change and lower unit oil guides walk you through both.

Mercury, Avalon and Harris all mention fogging oil. Avalon and Bennington describe spraying it into the spark plug holes; Mercury says to follow the fogging procedure in your operator's manual, because modern fuel-injected engines often have their own method. Don't improvise on an EFI engine; see the fogging guide.

Flush with fresh water using muffs or the approved fitting, then, as Mercury explains, tilt the motor all the way down so water trapped in the cooling passages drains out. An outboard left tilted up can hold water that freezes. Store it down (vertical) unless your manual says otherwise. The full outboard routine is in the outboard winterizing guide.

Avalon points owners to the grease fittings, often around the steering. Grease the steering, the outboard's tilt tube and swivel points and any other fittings your manuals list. The outboard grease points guide shows where they usually are.

Avalon notes that every Avalon pontoon has a drain plug at the bottom of each tube, which you can only reach with the boat out of the water. Many other brands have them too; some don't. With the boat on the trailer or blocked, open each plug (if fitted) and see if water comes out. Water in a tube can freeze over winter, and it means there's a leak to find. Avalon is clear that you also need to fix the source, which may mean a dealer or an aluminum welding shop. Reinstall the plugs unless your owner's manual says otherwise, and note any tube that had water. The pontoon tube leak guide explains how to find leaks.

Avalon warns that carpet, teak and vinyl breed mildew under a cover with little airflow. Clean seats with a vinyl-safe product, let them dry, then use a marine vinyl protectant. Lift seat cushions and open storage lids so air can circulate. Vacuum and dry the carpet or vinyl floor; look for soft spots in the deck while it's clean. See the pontoon deck and furniture guide.

Harris suggests a rodent repellent to stop mice chewing through the cover and upholstery, and Bennington suggests putting rodent bait on the deck. If you use bait, follow the label and remember pets, kids and wildlife; traps and deterrents are alternatives. Remove all food, seal openings you can, and check the boat during the winter. The rodent prevention guide has more.

Harris says to remove the battery, charge it fully and store it somewhere cool. Avalon adds topping it off during the winter, or, if the boat stays in the water, keeping it aboard and charged so any bilge pump keeps working. Drain livewells, washdown pumps, sinks and any freshwater system so nothing can freeze (see the freshwater winterizing guide if your pontoon has one).

Bennington says to keep the tubes off the ground to prevent corrosion, either on the trailer or on blocks placed under the tube welds. On a trailer, check the bunks, take weight off the tires if you can and look over the tires and bearings before storage. See the trailer tires guide.

Harris says year-round boaters need a good lift and a quality enclosure. In freezing areas, raise the boat fully out of the water before ice forms; never leave it sitting in ice. Unplug or switch off lift motors as your lift maker suggests. See the boat lift and in-water winter storage guides.

This is the pontoon-specific danger. Harris explains that a pontoon cover spans a wide, flat area; if rain or snow pools and the cover collapses, it can damage rails and trap moisture in the deck and furniture, which is worse than no cover. Bennington suggests building a frame from cheap lumber or PVC so the tarp sheds water, snow and ice. Bennington and Avalon both say a mooring cover is not meant for winter storage. Shrink wrap is the most weather-tight option and is usually a pro job. Leave vents so moisture can escape. Mercury's winter storage myths article adds two cautions: a cheap blue tarp isn't "better than nothing," because its woven surface rubs gelcoat, paint and the tube finish when it flaps, and it tears under snow (if you must use one in an emergency, pad the outboard cowl and furniture with old blankets under it); and don't wrap the gearcase in a plastic bag taped shut, since condensation collects under the plastic and can freeze. Leave the lower unit tilted down and open to the air or under a breathable cover. See the boat cover care and shrink wrap guides.