Freeze-Damage Prevention for Boats and Marine Engines

Draining water is not enough. For the best protection, run so-called, “RV” or “pink” antifreeze through engines and systems to help prevent freezing. John Tiger

It’s time to winterize your boat. Most important in the task list is to minimize the risk of something freezing and being damaged as a result. On most boats, it’s relatively easy to prevent this type of damage. Let’s take a look at some of the most common problems.

Sterndrive/Gear Case

After running the engine to winterize it, if all the water is not completely drained from the drive (for outboards, the gear case or lower unit), any water in the drive exhaust passage can easily freeze, expand and crack the housing. Therefore, be sure to trim the drive all the way down after running the engine for the last time, and watch to ensure all water drips out. Then, cover the prop hub opening with a plastic bag and/or wide tape, especially if you have to trim the unit up again to store the boat. Why? Rain water can enter the exhaust hub, freeze, expand and crack the housing.

Engine Block

Older inboards and sterndrives are particularly susceptible to freeze damage because the engine block drains can be partially clogged with rust flakes and other debris. It’s important to probe the drain with a pipe cleaner or similar instrument, and watch as the last dribbles of water drain out before calling it a season. For good measure, run “RV” (pink) antifreeze through the block as a last step.

Removing the freeze plugs from inboard and sterndrive engines is only one part of the process. Older engines drains may be partially blocked by rust, so use a small brush, pipe cleaner or other tool to make sure all the water is out. John Tiger Inboard/Sterndrive Exhaust Manifolds

Inboard and sterndrive exhaust manifolds and exhaust risers must be 100-percent completely drained. These are typically cast iron, so rust flakes can easily block the drain petcocks and passages. Running a small wire, tiny bristle brush or pipe cleaner into and out of each drain, as well as using RV pink antifreeze, will help prevent freezing and cracking due to water left in these components.

Water Heaters and Holding Tanks

If not completely drained, water heaters and holding tanks will also freeze and burst, or at least crack and therefore, need replacement. Running pink RV antifreeze through them as the last step will help keep freezing water out. For water heaters, you can purchase (or make) a bypass hose that allows you to use less antifreeze. Also, do not run antifreeze through any water filters.

Read Next: Dozens More Winterization Tips

Freshwater System

If your boat has a freshwater system for drinking water, shower, washdown, etc. then it’s vital to ensure that the drains, faucets, shower heads and hoses are all completely drained. Water left in any of these areas can easily freeze, expand and cause damage. If they leak water after cracking, other areas of the boat can be damaged as well. Running pink RV antifreeze completely through each system from one end to the other (for example, from the shower or washdown head all the way out the drain) will help keep the freeze out). Your saltwater washdown systems can also freeze and crack, depending upon your climate, so treat these the same way.

Drain the gearcase of outboards and sterndrives. If any water is discovered–indicated by “milky” looking lubricant, have the gearcase checked for leaks by a pro. Refill with fresh lube. John Tiger Bilge and Hull

If your boat is not tilted bow-up in storage, and enough water gets into the bilge and the hull and is trapped there (easy enough, if leaves and other debris are clogging the hull drain tube), it’s very possible the water there can freeze, expand and cause damage to the hull. The bilge pump can also be crushed or cracked from the expanding ice. Preventing this is relatively easy: Keep the boat tilted bow high, ensure the drain plug is removed, and keep debris from blocking the drains.

Bonus Water Trap—Batteries

Batteries should be removed from the boat and kept inside a warm garage, and charged per the manufacturer’s recommendation. Batteries left uncharged in a freezing boat may freeze, expand and crack, rendering them useless next season.

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