Winterizing Boat Engines: Avoiding Cold Damage

Boat engines can be damaged by cold temperatures, especially when water is present. The freezing of water within the engine can cause cracks in hoses, iron, and aluminium components. This can occur when the air temperature is below 28°F (-2°C) for an extended period. Saltwater and freshwater-cooled engines without proper coolant can freeze below 32°F (0°C) and 32°F (0°C) respectively. Proper winterization, including the use of antifreeze and stabilised fuel, is essential to prevent damage. Additionally, the duck hunter's freeze-up can occur when tilting the outboard traps water, which then freezes and causes engine damage.

Boat engines can freeze at different temperatures depending on the type of water in the engine

Engines that are not properly winterized run the risk of severe damage, such as cracking, caused by water freezing inside. The temperature at which this happens depends on the type of water in the engine.

If you have an engine that is raw water-cooled in freshwater (from a lake or river) and water is left in your lines, then the temperature would have to fall below 32°F (0°C) for several hours. When that happens, the water inside will begin to freeze, which will lead to cracking the block.

Saltwater-cooled engines with some saltwater left inside don't freeze as quickly or at the same temperatures as freshwater. Saltwater freezes typically at temperatures below 27°F (-2.7°C).

If you are using antifreeze, the freezing temperature of your engine will depend on the water-to-antifreeze ratio. For example, you could use a 100% ratio of marine antifreeze that will protect your engine from freezing in temperatures as cold as -50°F (-45.5°C). Some brands will even protect your engine up to -100°F (-73°C). Now, that is only if you can get 100% of the water out of the engine block and lines. If any water is left inside, that would mix with the antifreeze and dilute it so that it will freeze sooner. Another example is if you have a 50-50 ratio of water and antifreeze in the engine, the temperature at which the combination might start to freeze between -20 to -35°F (-28.8°C to -37.2°C), even though the antifreeze is rated for -50°F (-45.5°C) temperatures.

To determine the freezing temperature of your engine, you can buy an inexpensive tool called a hydrometer that will accurately tell you what your freezing point is based on what you have in your engine.

In summary, boat engines can freeze at different temperatures depending on the type of water in the engine and the presence and ratio of antifreeze. Taking the proper precautions, such as winterizing your boat and using the correct type and ratio of antifreeze, can help prevent freeze damage.

The water inside the engine is what freezes and causes damage

It's important to clarify that your boat engine doesn't actually freeze. A lump of cast iron or aluminium left in the deep, deep cold will not be harmed unless it's subject to sudden, violent changes in temperature or physical damage. It's the water inside your engine that freezes, and this can damage improperly winterised and un-winterised engines.

Water expands when it freezes, and the force it exerts is strong enough to split rubber hoses, crack iron, and rupture aluminium. When water freezes, it expands by about 9% in volume and converts to a non-compressible solid, which applies massive force to anything constraining it.

Your engine is anything but a solid block of metal. It has hollow pockets in the engine block called jackets where fresh cooling water and coolant flush to take away heat. Saltwater comes into heat exchangers, oil coolers, and other raw water-cooled components. These components are connected with hoses and channels to move the fresh and water cooler around.

Water left in these spaces is what freezes. The freezing water expands, which can crack everything from intake hoses to engine blocks.

To keep an engine from freezing, you must remove all the freezable water or blend/replace it with something that lowers the freezing point well below normal outdoor temperatures.

In theory, you could winterise your engine by blowing all the water from the various engine block jackets, coolers, and hoses. However, in practice, getting all the water out is tricky and unreliable. It's better to flush existing systems out with antifreeze to ensure it fills all water jackets and tubes with something that won't freeze in normal conditions.

Propylene glycol-based antifreeze will form an icy slush well before it freezes solid. The slush doesn't expand and cause damage to boat systems. But a -50°F antifreeze may start "freezing" at 12°F to 18°F (-11°C to -7°C) and form slush, and a -100° may start to slush at -58° to -63°F (-50°C to -52°C).

The damage caused by freezing water can be severe

Water left in the engine block, manifolds, and water pump can freeze and expand, which can crack everything from intake hoses to engine blocks. The engine block is anything but a solid block of metal. It has hollow pockets in the engine block called jackets where fresh cooling water and coolant flush to take away heat. Saltwater comes into heat exchangers, oil coolers, and other raw water-cooled components. These components are connected with hoses and channels to move the fresh and water cooler around.

Water left in these spaces is what freezes and causes damage. To keep an engine from freezing, you must remove all the freezable water or blend/replace it with something that lowers the freezing point well below normal outdoor temperatures. This is why it is important to winterize your boat engine.

One common issue in freezing weather is the "duck hunter's freeze-up", which occurs when tilting up the outboard traps water in the motor. In sub-freezing temperatures, this water freezes and can cause severe engine damage. Always keep your motor in the down position when not running to prevent water from freezing inside.

There are several steps to prevent a boat motor from freezing

How to Prevent Your Boat Motor from Freezing

Winter weather can be challenging for boat owners, and boat motors are particularly vulnerable to freezing, which can cause severe damage. Here are several steps to prevent your boat motor from freezing and ensure a smooth boating experience all year round:

Winterize Your Boat Engine

Winterizing your boat engine is the first and most important step in preventing freeze damage. This process involves preparing your boat's engine and other systems for winter storage. Here are the key steps:

• Drain all water from the engine block and manifolds.
• Add a marine antifreeze solution to the engine block, manifolds, and water pump.
• Run the engine for a few minutes to circulate the antifreeze.
• Turn off the engine and disconnect the battery.
• Consult your owner's manual for specific winterization procedures.

Store Your Boat in a Covered Area

Storing your boat in a covered area is crucial for preventing freeze damage. A covered boat storage area will protect your boat from harsh weather and ice formation on the engine. Ideally, store your boat indoors in a heated building. Using a high-quality boat cover is another effective way to shield your engine from freezing temperatures, rain, snow, and wind.

Maintain Proper Battery Care

The battery is critical to your boat's electrical system, and proper maintenance is essential:

• Keep the battery fully charged and store it in a dry, cool place.
• Regularly check the battery's electrolyte levels.
• Remove the battery from your boat and store it indoors during winter.

Keep the Engine Compartment Dry

Moisture can lead to freezing damage, so it's important to keep the engine compartment dry:

• Regularly wipe down the compartment to remove standing water or moisture.
• Use moisture-absorbing products, such as silica gel or dehumidifying beads.
• Ensure all ventilation ports are clear and open for proper airflow.

Use Heat

In extreme weather conditions, using heat is an effective way to prevent freeze damage:

• Engine block heaters are designed to keep your boat's engine warm and can be installed in the engine block.
• Engine compartment heaters can be installed permanently or used as portable heaters.
• Space heaters can be used to heat the entire boat or just the engine compartment.

A heated cover blanket is the fastest way to prevent a boat motor from freezing

Engines can freeze in temperatures of 32°F (0°C) or lower, with cracks forming in the engine if it is exposed to this temperature for over 90 minutes. However, this varies depending on the type of water in the engine, with saltwater freezing at 28.4°F (-2°C) or lower, and freshwater freezing at 32°F (0°C) or lower.

How to Prevent Freezing

To prevent a boat engine from freezing, it is important to follow several steps, including removing the engine from the water, draining the engine of water, stabilising the fuel, changing the gear lube oil, and spraying the spark plug holes and carburetor inlets.

Heated Cover Blankets

Other Methods to Prevent Freezing

In addition to heated cover blankets, there are other methods to prevent a boat motor from freezing. One method is to use a light bulb in the engine compartment, although this may not be as effective as the blanket. Another option is to use a boat compartment heater, but these can pose a fire risk. It is also recommended to keep the motor in the down position when not in use to prevent water from freezing inside.

Frequently asked questions