Draining Boat Engine Blocks: Step-By-Step Guide For Beginners

Draining a boat engine block is a crucial step in winterizing your boat to prevent freezing and ensure the longevity of your engine. The process involves removing the block drain plugs and, in some cases, detaching the hoses to allow for a complete drainage of water from the engine. This is particularly important for boats used in salt water or freshwater lakes and rivers with salt content, as the water can contain chemicals and salt that can corrode the engine over time. While some boat owners choose to simply flush the engine with fresh water, others go a step further by also adding antifreeze to the engine block. This is done by pouring antifreeze into the thermostat housing until it comes out of the exhaust. This not only prevents freezing but also provides additional protection against corrosion. It is important to note that draining the engine block alone may not be sufficient to winterize the entire engine, and other steps such as changing the oil and fogging the engine may also be necessary.

Remove the block drains and probe to ensure they drain

To ensure that your boat engine block is drained, you will need to remove the block drains and probe them. This is a crucial step in the engine winterization process and will help prevent freezing and corrosion.

First, locate the block drains. These are usually found at the bottom of the engine block, often requiring a 9/16" wrench to remove. There should be one on each side of the block, close to where the oil pan meets the engine. For Mercruiser 5.7 engines, they are about six inches down from the manifold drains and may be attached to the knock sensor.

Once you have located the block drains, loosen them so they are hand-tight, and then start the engine. Let it run for a few minutes, and then, one by one, unscrew the block drains and use a probe to ensure they are clear of any debris or sediment. A piece of wire or a small gauge wire can be used to clear out any blockages and ensure the drains are functioning. It is important to do this for all the block drains to ensure complete drainage.

After probing and clearing the drains, tighten the drains back into place and then proceed to the next steps in the winterization process. This may include flushing the engine with antifreeze, draining other components like the power steering cooler, and other maintenance tasks.

It is worth noting that some boat owners choose to simply flush their engines with fresh water after each use, particularly if they are using their boats in freshwater lakes or rivers. This can help prevent a build-up of salt and other chemicals, reducing corrosion. However, for those in colder climates, fully draining the engine block and ensuring it is clear of water is essential to prevent freezing and potential engine damage.

Remove hoses at the bottom of the manifolds to drain

To drain the manifolds, you will need to remove the hoses at the bottom of the manifolds or remove the drain plugs. This will allow you to drain the manifolds, risers, and/or engine block.

It is important to ensure that all water is drained from the engine to prevent freezing and potential damage during winter. One way to do this is by removing the hoses at the bottom of the manifolds.

• Prepare the engine: Run the engine up to operating temperature, then shut it down.
• Locate the hoses: Identify the hoses at the bottom of the manifolds. These hoses will need to be removed to drain the manifolds and engine block effectively.
• Remove the hoses: Use the appropriate tools to carefully remove the hoses from the bottom of the manifolds. You may need to loosen any clamps or fittings holding the hoses in place.
• Drain the water: Once the hoses are removed, allow the water to drain out completely. You may need to tilt or adjust the position of the engine to ensure all water is drained.
• Inspect and clean: Take this opportunity to inspect the hoses and manifolds for any debris, crud, or rust buildup. Use a nylon wire tie or a small gauge wire to remove any blockages and ensure the hoses and manifolds are clear.
• Reattach the hoses: Once you are satisfied that the manifolds and hoses are clean and free-flowing, carefully reattach the hoses to the bottom of the manifolds. Ensure all connections are secure and tight to prevent any leaks.

By following these steps, you will effectively drain the manifolds and engine block by removing the hoses at the bottom of the manifolds. This will help protect your boat engine during the winter season and ensure its longevity.

Remove the drain plugs to drain manifolds/risers

To drain manifolds/risers, you must remove the drain plugs. This is a crucial step in the process of draining a boat engine block and preparing it for winter.

The drain plugs are located at the bottom of the manifolds. You will need to remove the hoses at the bottom of the manifolds to access these plugs. Alternatively, you can remove the drain plugs from the risers, which are located about six inches down from the manifold drains, where the oil pan meets the motor. These plugs usually take a 9/16" wrench to remove.

Before removing the drain plugs, it is recommended to run the engine until it reaches operating temperature. Then, shut down the engine and remove the plugs, allowing the water to drain out. You can use a nylon wire tie or a piece of wire to probe the drain holes and remove any crud or debris that may be blocking them. This step ensures that the water can drain out completely.

Once you have removed the drain plugs and ensured that the holes are clear, let the engine sit for a few minutes to allow any remaining water to drain. After that, put the drain plugs back in, and your manifolds/risers will be drained!

Backfill the engine block and manifold with antifreeze

Backfilling the engine block and manifold with antifreeze is a crucial step in winterizing your boat's engine to prevent freezing and corrosion. Here's a detailed guide on how to do it:

Before you begin, ensure you have the necessary tools and materials, including RV antifreeze, a bucket, a hose, and any required adapters. It is also recommended to have a helper to assist with the process. Begin by draining the engine block and manifolds of any remaining water. This can be done by removing the drain plugs and hoses at the bottom of the manifolds. It is important to ensure that all water has been drained to prevent freezing and potential engine damage.

Once the engine is thoroughly drained, replace the drain plugs and tighten them securely. Next, prepare your antifreeze mixture by filling the bucket with RV antifreeze. It is important to use RV antifreeze as it is environmentally friendly and specifically designed for marine use. Do not mix the antifreeze with water; use it in its concentrated form. You will need enough antifreeze to fill the engine block and manifolds completely.

With the antifreeze ready, attach one end of the hose to the bucket and the other end to the thermostat housing or the intake manifold. Ensure all connections are secure to prevent leaks. Start pouring the antifreeze into the engine through the hose. Continue pouring until antifreeze begins to come out of the exhaust, indicating that the engine block and manifolds are filled.

At this point, you can stop pouring the antifreeze. Detach the hose from the engine and securely replace the cap on the thermostat housing or intake manifold. Give the engine a final inspection to ensure all drain plugs and hoses are securely in place. By following these steps, you will have successfully backfilled your boat's engine block and manifold with antifreeze, providing protection against freezing and corrosion during the winter months.

Remove the large hose from the therm housing side and pour antifreeze into the block

To remove the large hose from the therm housing side and pour antifreeze into the block, follow these steps:

First, locate the large hose at the front of the motor. This hose connects the motor-mounted water pump to the thermostat housing. Remove this hose from the thermostat housing by unscrewing it or pulling it off. Ensure that the boat is level to facilitate effective draining.

Next, remove the block drain plugs on both sides of the engine block near the oil pan area. These are usually located in the middle of the block from front to back and are often 9/16" plugs that can be removed with a wrench. With the block plugs removed, allow the water to drain completely from the engine block.

Once the block is drained, re-attach the large hose to the thermostat housing. Pour RV antifreeze into the hose until it comes out of the thermostat housing. Use about one gallon of antifreeze for this step. Ensure that all small hoses at the thermostat are also filled with antifreeze to reach every part of the engine.

Finally, put the block drain plugs back in, and you're done! This process will help protect your boat engine from freezing temperatures and corrosion during winter storage.

Frequently asked questions