Antifreeze For Boat Engines: Necessary Maintenance Or Not?

Adding antifreeze to your boat engine is an essential step in winterizing your boat to prevent costly repairs and extend the life of your engine. The main applications of antifreeze include the winterization of potable water systems, sanitation systems, cooling systems, non-running boat engines, and air conditioners. Antifreeze is necessary to prevent water in the engine from freezing and causing a cracked block, necessitating engine replacement. The chemical in antifreeze that resists freezing is either ethylene glycol or propylene glycol. While ethylene glycol is effective, it is toxic and harmful to the environment. Propylene glycol is a safer, non-toxic, biodegradable alternative that is better suited for marine use. It is important to follow the manufacturer's recommendations for your locality when mixing antifreeze with water, typically a 50/50 mix.

The benefits of propylene glycol vs ethylene glycol

Boat engines require coolant to prevent freezing, boil-over, and corrosion, as well as to prevent the formation of limestone deposits and foaming. The coolant, or antifreeze, used in boats can be either ethylene glycol or propylene glycol. While both types of antifreeze can be used in boats, there are some key differences and benefits to using propylene glycol.

Benefits of Propylene Glycol

Propylene glycol is a safer, non-toxic alternative to ethylene glycol. It is odorless, tasteless, biodegradable, and environmentally friendly, making it ideal for use in lakes and rivers. It is also non-corrosive to engines and does not require special disposal procedures like ethylene glycol, which is poisonous to pets, wildlife, and the environment.

Propylene glycol is recommended for winterizing boat engines as it provides excellent freeze protection. It is also suitable for potable water systems, sanitation systems, cooling systems, and air conditioners.

Benefits of Ethylene Glycol

Ethylene glycol is a good antifreeze/coolant option, offering efficient heat transfer capabilities. It has a higher density than propylene glycol, allowing for better heat absorption from the engine. It is also more cost-effective to produce.

While ethylene glycol has better heat transfer capabilities, propylene glycol offers superior safety, effectiveness, and environmental benefits, making it a preferred choice for marine applications, especially during winterization.

How to winterize a raw-water-cooled engine

Winterizing your boat engine is essential to prevent damage from freezing temperatures. Here are the steps to properly winterize a raw-water-cooled engine:

Step 1: Change the Oil and Oil Filter

Before laying up your boat for the winter, change the oil and oil filter. First, run the engine for a few minutes to lower the oil's viscosity and allow it to pick up any impurities. Then, shut off the engine, change the oil, and replace the filter. Finally, restart the engine and run it for about a minute to circulate the fresh oil to internal parts.

Step 2: Change the Fuel Filter and Stabilize the Fuel

Replace the fuel filter and/or change the fuel filter canisters. Check for leaks while the engine is running. If your boat uses gasoline with ethanol (E10), consider emptying the tank as ethanol will absorb moisture over the winter and can separate from the gasoline, causing potential engine damage. If emptying the tank is not practical, add a stabilizer to prevent oxidation and fill the tank to 95% to allow for expansion.

Step 3: Drain the Water or Use Antifreeze

This step can be done in two ways: by draining the system or by using antifreeze.

Draining the System

Thoroughly drain the engine by locating and opening all petcocks. If water fails to drain freely, check for clogs and clear any blockages. Don't forget to drain the sea strainer, seacock body, and water lift muffler.

Using Antifreeze

This method is preferred for inboard engines as it better protects the engine and reduces the risk of freeze damage. You will need a five-gallon bucket and enough non-toxic antifreeze (propylene glycol) for your engine and plumbing (at least two gallons).

• Close the intake seacock if the boat is in the water.
• Fill the bucket with undiluted antifreeze.
• Remove the raw water intake hose from the seacock and insert it into the antifreeze in the bucket.
• Start the engine and run it at idle until antifreeze discharges from the exhaust outlet for at least 30 seconds.
• For gasoline engines, fog the cylinders, which should stop the engine.
• Reattach the intake hose to the seacock.
• For gasoline engines, use engine fogging fluid or light motor oil, and some plastic sheeting and duct tape.
• Turn off the fuel valve halfway through the process to run the carburetor dry.
• Spray the fogging fluid into the flame arrester for the last 10 seconds of engine operation.
• Wrap duct tape around the flame arrester and cover the engine with plastic after it has cooled to prevent corrosion.

Additional Tips

• Consult your engine's owner's manual for specific winterizing instructions.
• Fill fuel tanks and add stabilizers to gasoline.
• Check coolant levels in the freshwater-cooling system and add coolant if needed.
• Make sure water strainers are filled with antifreeze.
• Change the oil and filter, and check hydraulic fluid levels.
• Always dispose of hazardous wastes properly.

How to winterize a freshwater-cooled engine

Winterizing your boat engine is essential to prevent damage caused by freezing temperatures. Here is a step-by-step guide to properly winterize a freshwater-cooled engine:

Step 1: Prepare the Boat

Place your boat on a trailer or haul it out and block it level to ensure the raw-water side of the cooling system will drain. Any remaining water could freeze and cause cracks in the cooling system components.

Step 2: Drain the Raw Water Side

Fully drain the raw-water side of the engine, including the manifolds, seawater pump, and heat exchanger. The drain plug locations vary by engine, so refer to your owner's manual. Disconnect the raw-water inlet hose and remove the drain plugs. Use a stiff wire to clear any sediment blocking the drain.

Step 3: Flush and Refill the Closed-Cooling Side

The closed-cooling side of the system contains an antifreeze-and-water solution. According to the engine's maintenance schedule, flush and refill this side. Check the antifreeze/water ratio; a drop in concentration may indicate a leak in the heat exchanger. Refer to the owner's manual for the proper ratio recommended for your region.

Step 4: Fuel System and Fogging

Add a fuel stabilizer to the tank and run the engine to circulate the treatment. Shut it off and let it cool. "Fog" the engine by adding five gallons of gas, two quarts of TC-W3 two-stroke oil, and five ounces of fuel stabilizer to a six-gallon remote tank. Connect the remote tank and run for five minutes at 1,300 rpm. Then, shut down and replace the oil, filter, and fuel filter.

Step 5: Air-Activated Draining (if applicable)

Some engines offer air-activated drainage using a supplied hand pump. Lock the pump onto the actuator fitting and pressurize the system. Crank the engine without starting to purge the seawater pump. Remove the hand pump.

Step 6: Fill the Raw-Water Side with Antifreeze

After draining, replace the plugs. Fill with a propylene glycol antifreeze containing rust inhibitors to protect areas where raw water might sit. Place a motor flusher ("earmuffs") over the water pickups, connected to a bucket of antifreeze. Run the engine on your winter-mix fuel tank until the pink antifreeze solution exits the exhaust.

Step 7: Battery Storage

Remove and charge the batteries. If they don't hold a charge, consider replacing them in the spring. Clean the terminals with a wire brush, water, and baking soda. Coat the terminals with light grease and check the battery cables for any damage or corrosion.

Step 8: General Maintenance and Inspection

Consult the owner's manual for any additional maintenance steps. Inspect the engine, drive, steering, and tilt-and-trim systems. Check the belts, wires, shift cables, exhaust manifolds, hoses, and bellows for any wear, cracks, or corrosion. Check the hydraulic fluid levels in the power steering and trim pumps. Inspect the fuel hoses and replace if necessary.

Step 9: Winterize the Freshwater System

Turn on the water pump and let all water fixtures run until the tank is empty. Fill the tank with antifreeze. Turn on the hot water side of the fixture furthest from the water pump and let the antifreeze flow. Once antifreeze is flowing, close the hot side and open the cold side, repeating the process until antifreeze comes out. Repeat this for all fixtures, working your way back to the one closest to the water pump.

How to check your coolant

Checking your boat's coolant level is a critical but often overlooked task that can ensure your engine operates properly and prolong its life. Here is a step-by-step guide on how to check your coolant:

• Ensure the Engine is Cool: Before checking the coolant, make sure your boat's engine is completely cool. Wait at least 30 minutes after turning it off, and longer if the engine has overheated. Working with a cold engine is essential for safety.
• Locate the Expansion Tank: Find the expansion tank or coolant reservoir. Refer to your boat's handbook or owner's manual if you're unsure. Adding coolant to the wrong reservoir can cause damage.
• Check the Coolant Level: Look at the side of the expansion tank. The coolant level should be between the "min" and "max" marks. If it's below the minimum, you'll need to top it up. A low coolant level can also affect your boat's heater, causing cool air to blow even when set to "hot."
• Inspect Hoses and Connections: While checking the coolant level, take a moment to inspect the hoses and connections for any signs of leaks or problems. Look for wetness or white staining, which could indicate a potential issue.
• Top Up the Coolant if Necessary: If the coolant level is low, you'll need to add more. Only do this when the engine is cold to avoid the risk of scalding from hot, pressurised water. Use the correct type of antifreeze—different types don't mix well. Remember that antifreeze not only protects your engine in winter but also helps prevent corrosion and scale build-up year-round.
• Consider a Professional Inspection: If you notice that your coolant level has dropped, it's a good idea to have your boat inspected by a professional at a garage or marine service centre. It's not typical for the coolant level to decrease, and this could indicate a larger issue.

To ensure the proper ratio of antifreeze to water in your coolant, you can use testing tools such as a ball gauge, coolant test strips, a refractometer, or a hydrometer. These tools can help you verify that your coolant is effective and provide adequate protection against freezing and boiling.

How to prevent corrosion

Corrosion is the arch-enemy of any boat owner, and it's a persistent foe that can affect both the inside and outside of your boat's engine. Here are some detailed, direct, and instructive ways to prevent corrosion:

Keep it Clean

• Wash your boat thoroughly with soap and fresh water after every trip.
• Pay special attention to metal components like railings, rod holders, and hinges, using a soft-bristle brush.
• Flush your boat's engine after every outing to remove any salt water from the cooling system.
• For saltwater boating, rinse the entire engine with clean water and, if needed, a mild soap.
• Use an external boat engine cleaner, followed by a silicone spray, to protect the metal surfaces.
• Keep your boat covered, whether in a slip or on a trailer.

Keep it Protected

• If your boat is stored in a slip, tilt the outboard or I/O lower unit to its highest position so that the running gear isn't constantly submerged in saltwater.
• Towel-dry your boat after washing and install a custom-made cover to prevent rainwater pooling and condensation.

Watch Your Zincs

• Know where the sacrificial zinc anodes are on your boat, and replace them if they're degraded.
• These zinc "tabs" are usually found on the engine lower unit and transom but can also be found inside the engine compartment and elsewhere.
• Check your boat and engine owner's manual to confirm the number and location of these anodes.
• Sacrificial anodes corrode before your engine does, so they must be replaced regularly with high-quality, factory-recommended replacements.

Lubricate

• Lubrication protects against water intrusion and rust.
• Apply marine grease to the fittings on your outboard steering tilt tube and engine trim mechanism.
• Periodically apply a light coat of moisture-displacing lubricant to moving metal parts such as latches, hinges, and linkages.

Protect Your Engine & Fuel System

• Add a fuel system treatment, such as Techron Marine Protection Plus Fuel System Treatment, to your gasoline-powered boat's fuel tank.
• Store your boat with a full tank of fuel (95% or more) and inspect fuel system components such as fuel lines, fittings, and hose clamps.
• Change your coolant every five years or after 1,000 hours of use.
• Check your coolant regularly and maintain a proper ratio of antifreeze to water.

Remember, the key to preventing corrosion is regular maintenance and vigilance. Always keep your eyes open for signs of corrosion and act quickly to correct it.

Frequently asked questions