Winterizing Your Mercruiser: A Step-By-Step Guide

Winterizing your boat is essential to protect your engine and other components from damage when temperatures drop below freezing. This process is especially important for boats with Mercruiser engines, as improper winterization can lead to costly repairs. Even in milder climates, winterization is an excellent opportunity to perform annual maintenance to ensure reliable performance when the boating season arrives. This includes tasks such as changing the engine oil, treating the fuel system, and applying corrosion inhibitors. By following the manufacturer's recommendations and taking the necessary steps, you can rest assured that your boat will be ready for adventure on the water come spring.

How to Winterize a Boat with a Mercruiser Engine Inboard

Drain the engine

Draining the engine is a crucial step in winterizing your boat with a Mercruiser engine inboard to prevent water in the cooling chambers from freezing and causing damage. Here's a detailed guide on how to do it:

Locate the Drain Plugs

Begin by locating the petcocks or drain plugs on your engine. These are usually found underneath the manifolds and on the sides of the engine block. Some engines may have bronze plugs similar to bilge plugs.

Open the Drain Plugs

Once you've located the drain plugs, open them to allow water to drain from the cooling passages. Be sure to remove all plugs to ensure complete drainage.

Remove the Water Pump Hose

To facilitate drainage, remove the water pump hose from the bottom of the water pump. This will allow the water to drain completely from the system.

Check for Remaining Water

Even after draining, some water may remain in the cooling pipes or hoses outside of the engine block. If you're unsure whether all the water has been removed, it's recommended to run antifreeze through the system as an additional precaution.

Use Antifreeze (Optional)

If you're concerned about any remaining water in the engine, you can run antifreeze through the cooling system. Prepare a mixture of propylene glycol according to the manufacturer's recommendations to protect the engine from freezing temperatures. Use a gravity flow device that connects to a garden hose, or follow the instructions provided by the dealer for your specific engine model. It is crucial to displace all water from the cooling system to prevent freezing and potential damage.

Refer to the Manual

Always refer to your engine's manual to ensure you have identified and removed all necessary drain plugs. Each engine model may have unique drainage requirements, so it's important to follow the specific instructions provided by the manufacturer.

By following these steps, you can effectively drain the engine of your Mercruiser inboard boat and help protect it from potential freezing damage during the winter season.

Change the engine oil

Changing the engine oil in a Mercruiser inboard engine is a straightforward process, but it requires attention to detail and the right tools for the job. It is recommended to change the engine oil at least once a year or every 100 hours of use, whichever comes first. This process is important to maintain the performance and longevity of your engine. Here is a step-by-step guide on how to change the engine oil:

Step 1: Prepare the Engine and Work Area

Before beginning, make sure to read the owner's manual for safety precautions and specific instructions for your Mercruiser model. Inspect your engine and check the oil level. Ensure that the propeller has been removed and that the area is clear of people and pets. Check for fuel or fuel vapors and ensure adequate ventilation to prevent carbon monoxide poisoning. Cover the floor and cushions with old towels or blankets to catch any spilled oil.

Step 2: Warm Up the Engine

Start the motor and let it run until it reaches operating temperature. This will warm up the oil, making it easier to drain. Once the engine is warm, turn it off and let it cool down for a few minutes.

Step 3: Drain the Old Oil

Remove the dipstick and attach an oil hand pump or an electric oil changer to the dipstick tube. Suck out the old oil into a suitable container. Be careful as the oil may be hot. Mercruiser dipstick tubes are also designed for oil withdrawal, so you can drain the oil through the dipstick tube.

Step 4: Replace the Oil Filter

Using the correct filter wrench, remove the old oil filter by turning it counterclockwise. Inspect the mounting area and wipe it clean with a lint-free towel. Make sure to remove the old filter o-ring. Compare the new filter to the old one to ensure you have the correct type. Coat the o-ring on the new filter with clean oil, then thread it into place by hand until it's tight. Use the filter wrench to tighten it further by about 3/4 of a turn. Do not over-tighten as this will make removal difficult next time.

Step 5: Refill with New Oil

Check your owner's manual or the capacity decal on the engine to determine the correct type and amount of oil required. Fill the engine with the specified amount of oil. Let the engine sit for a few minutes to allow the new oil to settle. Reinstall the oil fill cap and perform a general inspection of the engine, ensuring that the filter is installed correctly and that all tools and rags have been removed.

Step 6: Start the Engine and Check Oil Level

With a water supply connected to the motor, start the engine and inspect for any oil leaks. Observe the oil pressure gauge to ensure proper readings. Let the engine warm up to operating temperature. Turn off the engine and let it sit for a few minutes. Check the oil level with the dipstick and add more oil if needed.

Step 7: Clean Up and Enjoy Your Boat

Clean up any spilled oil and dispose of the old oil and filter properly. Consult your local guidelines for waste disposal. Now you're ready to enjoy your boat on the water! Remember to follow the maintenance schedule in your owner's manual for optimal performance and engine longevity.

Run antifreeze through the engine

To run antifreeze through the engine, you will need to prepare a 50:50 mix of water and non-toxic propylene glycol plumbing antifreeze. Close the raw water seacock and disconnect the raw water intake hose from its strainer. Stick the hose into the bucket of antifreeze. Have someone else start the engine and run it for a few seconds until you see antifreeze beginning to trickle out of the exhaust pipe. Then, turn off the engine. This process will protect the raw water side of the heat exchanger from damage in freezing weather.

If your engine has a water-lift muffler, drain any remaining water or antifreeze from it.

If you are using engine coolant, you will need to be cautious as it is highly toxic and can cause blindness or even death. It also has a sweet taste and smell that can attract children and pets. Be sure to capture the waste coolant and dispose of it properly.

If you are replacing the coolant with fresh coolant, it is recommended that you fill the engine with fresh water and run it for a few minutes to circulate and rinse it. Then, when the engine has cooled, repeat the previous steps before refilling with fresh coolant.

Drain the engine block and manifolds

To drain the engine block and manifolds of a boat with a Mercruiser engine inboard, you will need to remove the block drain plugs and hoses. This will ensure that all water is drained from the engine to prevent it from freezing and causing damage during the winter.

First, locate the block drain plugs on both sides of the engine near the oil pan area. Remove these plugs and probe the area to ensure that the water is draining. You may need to poke out the drain holes with a small tool to dislodge any rust or sediment that could be blocking them.

Next, locate the large hose that connects the motor-mounted water pump to the thermostat housing. Remove this hose from the thermostat housing and bend it down to drain any water that is inside.

Additionally, remove the small hoses at the thermostat and fill them with antifreeze to ensure that all nooks and crannies are protected. You can also fill the large hose with antifreeze and pour it into the block until it comes out of the thermostat housing. Use RV antifreeze and approximately one gallon should be sufficient.

Finally, if your engine has a seawater cooling system, it is crucial to drain this as well. Follow the instructions specific to your engine model and fill the system with propylene glycol per the manufacturer's recommendations to protect the engine from freezing temperatures.

Change the gear-case lubricant

Changing the gear-case lubricant is a necessary part of winterizing your boat with a Mercruiser engine inboard. This process should be done annually or after every 100 hours of use. It is important because it removes diminished additives and contaminants from the engine and helps to prevent corrosion.

To change the gear-case lubricant, start by placing a clean oil drain pan under the engine to catch the old lubricant as it drains. You will then need to remove the lower drain plug and the top oil vent plug, allowing the unit to completely drain. It is important to use a large screwdriver for this step to avoid slipping and potentially ruining the screw slot, which will make future removals and reinstalls difficult. Once the unit has drained, inspect the old lubricant for any signs of water contamination or metal particles. If the lubricant appears milky or creamy, this is an indication that water is present and the propeller shaft seal may be compromised. In this case, it is recommended to have the gearcase inspected by a professional technician.

Once you have inspected the old lubricant, it's time to add the new lubricant. This is done by filling the gearcase from the bottom-up until the lubricant flows out of the top/side vent hole. Be sure to use a heavy-duty pump or the plastic tube that comes with the quart oil container to fill the gearcase. Fill slowly and wipe up any drips with a clean rag. Once the gearcase is full, install the top vent plug with a new gasket and tighten. If your drive has an internal drive lube monitor bottle, continue to pump lubricant until there is approximately one inch of lubricant in the monitor bottle. Finally, remove the lube fill pump from the bottom hole and quickly install the bottom plug with a new gasket.

Frequently asked questions