How To Winterize Your Boat With Antifreeze

Winterizing your boat is essential to prevent damage from freezing temperatures. One of the key steps in this process is using antifreeze to protect the engine and other components. But it's not as simple as pouring in any type of antifreeze—choosing the right kind and following the correct procedure are critical to ensure your boat survives the cold weather. So, do you put antifreeze in your boat to winterize it? The short answer is yes, but there's a lot to consider when selecting and applying this essential product.

The importance of winterizing your boat

Winterizing your boat is crucial, especially if you live in a region where the water freezes during the colder months. By taking the necessary steps to prepare your boat for winter, you can avoid costly repairs and extend the life of your vessel. Here are some key reasons why winterizing your boat is essential:

Prevent Engine Damage

Cold temperatures can cause residual water in your boat's engine, plumbing, and body to freeze and expand, leading to catastrophic damage. Water freezing within the engine block can result in cracked blocks, rendering the engine useless. Winterizing your boat involves removing excess water from these areas and adding antifreeze to prevent freezing and expansion. This process is critical for both raw water-cooled engines, which run water directly through the engine, and closed-system inboards, which use a heat exchanger to cool the engine.

Protect Fuel System

The ethanol additives in modern gasoline can cause issues when left sitting for long periods during winter. This can lead to a process called phase separation, where the ethanol absorbs water and separates from the gasoline, creating a layer of water and ethanol at the bottom of the fuel tank. This can result in engine performance issues and even hydro lock, potentially destroying the engine. Winterizing your boat includes stabilizing the fuel and filling the tank to prevent phase separation.

Engine Fogging

"Fogging" your engine involves spraying a waxy fogging oil into the engine intake and carburetors while it is running. This process coats the pistons, piston walls, and other internal components, protecting them from corrosion during the winter months. It also provides an opportunity to run stabilized fuel through the engine, ensuring it stays in optimal condition until spring.

Preserve Other Boat Systems

Winterizing your boat also involves taking care of other systems, such as the marine head, septic system, and freshwater system. By running antifreeze through these systems, you prevent freeze damage and ensure they are clean and sanitized for the next boating season. Additionally, it is essential to properly store your boat with a fitted cover or tarp to protect it from the elements.

Peace of Mind

By investing time and effort into winterizing your boat, you gain peace of mind knowing that your vessel will be safe and secure during the off-season. Proper winterization ensures that your boat's engine, fuel system, and other components are well-maintained and protected from the harsh winter weather. This will save you from potential repair bills and headaches when the boating season arrives.

The types of antifreeze suitable for boats

There are two main types of antifreeze: ethylene glycol (EG) and propylene glycol (PG). The former is toxic and should not be used in boats, especially those that use a raw water cooling system. This is because, in the event of a leak, the antifreeze could end up in the water and harm the environment.

Propylene glycol is a safer, non-toxic option for boats. It is also biodegradable, odourless, and tasteless. It is slightly more expensive than ethylene glycol, but it offers a combination of safety and effectiveness that makes it a superior choice for marine use.

When choosing an antifreeze for your boat, it is important to select a product that offers freeze protection for the climate you will be operating in. Some products offer protection down to -50°F, while others are rated for -60°F or -100°F.

• STAR BRITE 31400 Antifreeze
• RecPro RV Antifreeze
• TRUEGARD Marine RV Antifreeze
• SPLASH 619526 RV & Marine Antifreeze
• Camco 30757 RV and Marine Antifreeze
• PEAK RV and Marine Antifreeze

Steps to winterize inboard boats

Winterizing your inboard boat is essential to prevent gunk buildup, keep condensation out of the fuel tank, and maintain a healthy engine. Here are the steps to properly winterize your inboard boat:

Prepare Your Inboard Boat Motor for Winterizing:

Fill the tank with gas to minimize the chance of air and moisture getting into the tank, which can cause water to enter the engine and lead to severe problems. Add a fuel stabilizer to prevent buildup in fuel lines, injectors, and carburetors. Warm up your engine by running it in the water or using an adaptor or motor muffs with a hose for the water supply.

Add Antifreeze and Spray Fogging Oils:

Apply non-toxic propylene glycol antifreeze to the engine to prevent water condensation from freezing and causing expansion, which can lead to cracks. Drain the engine block and then add the antifreeze. If your boat has a sterndrive, additional steps are required to protect the lower parts. Drain the lines by leaving the sterndrive stored in a down position. Allow the engine to reach operating temperature so that the thermostat opens, and coolant and fuel stabilizer can circulate through the lines, carburetors, and injectors. Spray fogging oil into the engine while it's still warm. Fill a five-gallon bucket with non-toxic antifreeze, close the intake seacock, and transfer the hose to the bucket. Let the boat engine idle until the bucket is almost empty and antifreeze is discharged from the exhaust.

Change the Engine's Oil and Replace Oil Filter:

Changing the oil and filter is easier when the engine is warm. Check for leaks by running the engine with a continuous water supply. If a leak is found, turn off the engine and make repairs. Restart the engine and let it idle to reach regular temperatures without over-cooling it too quickly.

Final Inspection:

Check the exhaust system for corrosion and ensure the raw water injection hose is not obstructed. Inspect hoses and hose clamps for any damage, cracks, shredding, or rust, and replace them if necessary. Seal any openings, such as the air inlet and exhaust outlets, with tape to prevent the buildup of damp air and water condensation.

Additionally, don't forget to take care of the battery, plan for pest control, invest in a quality winter boat cover, and take theft prevention measures.

Steps to winterize sterndrive boats

Winterizing your sterndrive boat is essential to protect your engine and drive from damage during the offseason or long-term storage. Here are the detailed steps to properly winterize your sterndrive boat:

Drain Residual Water:

• Run the engine on a flusher and bring it to operating temperature to open the thermostat.
• Place the boat on a trailer or level surface, and trim the drive down.
• Turn the drive dead astern to drain water from the pickup, water pump housing, and exhaust passages.
• Crank the engine slightly without starting it to purge water from the water pump.
• Keeping the drive down prevents rainwater or snowmelt from collecting in the exhaust hub.
• Use a small wire to ensure all water drains from the drive's vents and holes.

Fill with Antifreeze Solution:

• Use propylene glycol antifreeze with a rust inhibitor, mixed according to the manufacturer's instructions.
• Attach a flush device ("ear muffs") to the drive's water pickups, connecting it to a five-gallon bucket containing the antifreeze solution.
• Run the engine until the pink propylene glycol solution comes out of the drive's exhaust.
• Turn off the engine.

Drain and Replace Gear Lube:

• Remove the lube drain/fill and vent plug screws to drain the gear lube.
• Install new gaskets on the plug screws.
• If you have a remote gear lube reservoir, remove, drain, clean, dry, and reinstall it.
• Pump fresh lube into the drive from the drain hole until it appears at the vent hole.
• Install the vent screw to create a partial vacuum, then quickly replace the drain/fill screw.
• Fill the lube reservoir to the proper level.

Check the Prop Shaft:

• Remove the propeller and check for fishing line around the shaft seal.
• Remove any line and inspect the seal for damage.
• If the seal is damaged or gear lube is leaking, have the seal replaced and the gears and bearings checked.
• Grease the shaft and send the propeller for reconditioning if needed.

Inspect and Service Other Components:

• Inspect the bellows, universal joint, gimbal bearing, shift cable bellows, water intake hose, and exhaust run.
• Replace the bellows, O-rings, and gaskets.
• Install a new water intake hose.
• Align the engine and drive.
• Lube the U-joint.
• Check the steering and tilt-and-trim components for wear and replace as needed.
• Inspect hydraulic fluid levels in the power steering and trim pumps.
• Check and replace sacrificial zinc anodes if less than 70% remains.
• Use zinc-chromate primer and touch-up paint on scratches or chips.
• Grease all grease fittings.

Additional Engine Maintenance:

• Change the engine oil and filter before long-term storage to remove acidic combustion byproducts.
• Replace the water-separating fuel filter.
• Check the coolant fluid level and concentration in the freshwater cooling system.
• Lubricate the propeller shaft splines and check for fishing line.
• Lubricate the engine coupler.
• Run your fuel tank almost empty and add fresh fuel treated with a stabilizer.
• Drain the engine seawater cooling system and fill with propylene glycol to prevent freezing and rust formation.

By following these steps, you will help ensure your sterndrive boat is properly winterized and protected during the offseason.

Steps to winterize outboard boats

Winterizing your outboard boat is crucial to protect it from damage during the winter. When the temperature drops, any water left in the boat will freeze and expand, which can cause cracking. Winterizing your boat will also prevent rust from forming on the metal parts of the motor. Here are the steps to properly winterize your outboard boat:

Check Your Engine Service Manual

First, refer to your engine's owner's manual or service manual for any special winterizing instructions. Outboard engines, such as four-stroke or direct-injected two-stroke models, may have unique winterizing, flushing, and maintenance requirements. Always follow the manufacturer's instructions specific to your engine.

Change Engine Oil and Oil Filter

Change the oil and oil filter to prevent residual moisture and contaminants from corroding your engine during storage. Begin by running the engine for a few minutes to warm up the oil and allow it to pick up any impurities. Then, shut off the engine, change the oil, and replace the oil filter. Finally, restart the engine and let it run for about a minute to circulate the new oil to all internal parts.

Flush the Engine

Flush the engine with fresh water using a flusher or by running it in a tank of clean water. This will remove any dirt, debris, or salt buildup. Be sure to follow the manufacturer's instructions for flushing, as some newer engines have a garden hose fitting that allows for flushing without starting the engine.

Fill the Gas Tank and Use Fuel Stabilizer

Fill your gas tank to 95% capacity and add a fuel stabilizer to prevent the gasoline from oxidizing and leaving varnish-like deposits. Fuel stabilizers also prevent ethanol in the gasoline from absorbing moisture, which can lead to phase separation and cause engine damage.

Fog the Engine with Lubricant

Fogging the engine involves injecting fogging oil or a storage lubricant through the carburetors or electronic fuel injection (EFI) system air intakes. This creates a thin film of lubricant that protects internal components such as bearings, seals, and rotating surfaces from corrosion. Continue fogging the engine until it stalls.

Store Engine in Trimmed Down Position

Store your outboard engine in the trimmed down (running) position. This position ensures that all water is drained from the cooling system. You may also want to cover your engine with a vented canvas cowling storage cover for added protection during storage.

Additional Tips

• Change the fuel filter and lower unit gear oil.
• Stabilize the fuel with products to prevent the formation of gum and varnish during storage.
• Flush the engine with antifreeze to prevent residual water from freezing and causing damage.
• Disconnect and charge the battery at least twice over the winter.
• Cover the engine with a waterproof tarp or canvas and store it in a dry place, if possible.

Frequently asked questions