Winterizing Your Boat: A Regional Guide

Winterizing keeps water from freezing inside your engine, plumbing, and cooling system. A cracked block or split manifold costs $2,000 to $8,000 to fix. Winterizing costs $300 to $500 per engine if you hire it out. It's one of the few jobs where the DIY savings are real, but the stakes for doing it wrong are high.

Who needs to winterize

If your area gets below 32 degrees for more than a few hours at a time, you need to winterize. That covers the entire Northeast, Midwest, and Pacific Northwest, plus parts of the Mid-Atlantic and mountain states.

South Florida, the Keys, Hawaii, and Southern California generally don't need winterization. The Gulf Coast is a gray area. Corpus Christi rarely freezes. Houston gets a hard freeze every few years. If you're on the Gulf Coast and your boat stays in the water, keep an eye on the forecast and have a plan.

Engine winterization by type

Outboard motors

Outboards are the simplest to winterize because the cooling water drains when you tilt the motor up. The key steps: run the engine with fresh water to flush salt and sediment, change the oil and filter, replace the fuel-water separator, add fuel stabilizer to a full tank, and fog the cylinders with fogging oil. Pull the propeller and grease the shaft. Spray the powerhead with corrosion inhibitor.

Inboard and sterndrive engines

These are more involved because the engine sits inside the hull and holds water in the block, manifolds, and heat exchangers. You need to drain or flush the raw water side of the cooling system with non-toxic antifreeze (propylene glycol, not automotive ethylene glycol). Run antifreeze through the engine until pink fluid comes out the exhaust.

On a sterndrive, drain the outdrive and add fresh gear lube. Inspect the bellows for cracks. A torn bellow is the number one cause of sinking on sterndrive boats.

Diesel engines

Same cooling system concerns as gas inboards. Change the fuel filters and fill the tank to prevent condensation. Diesel fuel absorbs water, and water in diesel causes microbial growth (diesel bug) that clogs filters and injectors. Add a biocide like Biobor JF if the boat will sit for more than three months.

Freshwater system

Drain the freshwater tank, hot water heater, and all lines. Open every faucet. Pump non-toxic antifreeze through the system until it comes out of each tap and the shower. Don't forget the raw water washdown and livewell pumps.

The rest of the boat

Remove the drain plug and tilt the bow up slightly so any rain or snowmelt drains out. Take the batteries home and put them on a maintainer. Clean the bilge. Remove all food, drinks, and anything that can mold. Leave hatches and lockers cracked open for air circulation, but not so far that rain gets in.

Shrinkwrap or cover the boat. A proper winter cover keeps snow load off the canvas and prevents UV damage. Shrinkwrap costs $12 to $20 per foot at most yards and includes a support frame so snow doesn't collapse the wrap onto the boat.

Cost summary

When to do it

Don't wait for the first freeze. In the Northeast and Great Lakes, boats come out between late September and mid-October. The yards fill up fast, so book your haul-out by August. If you miss the window and a surprise freeze hits while your boat is still in the water with raw water in the engine, you're looking at a very expensive spring.