Cooling Your Boat Engine: Tips For Summer Sailing

Keeping a boat engine cool is very different from keeping a car engine cool. Unlike cars, boat engines do not have radiators, so they use the water from below the vessel to cool down. This water is sucked up and run through the engine block, then exited through the exhaust and out the back or below the boat. This is known as a raw water cooling system. The alternative is a closed-loop cooling system, where the saltwater is sucked up and run through a series of heat exchangers, with saltwater on one side and coolant on the other. This coolant then runs through the engine, avoiding any saltwater from running through the block.

Check the thermostat

A boat thermostat is an important component of the engine cooling system. It regulates the temperature of the water or coolant in the engine, helping to prevent the engine from overheating and causing damage. If the thermostat is not functioning properly, it can lead to a range of problems, including engine damage, increased fuel consumption, and reduced engine performance. Therefore, it is crucial to regularly inspect and maintain the thermostat to ensure the proper functioning of the boat's engine.

• Turn off the engine and let it cool down completely before beginning the inspection. This is an important safety precaution.
• Locate the thermostat in the engine compartment. It is usually a small, metal device situated between the engine and the water pump.
• Check the thermostat for any signs of damage, such as corrosion, leaks, or damage to the gasket.
• Inspect the hoses connected to the thermostat for any wear and tear or leaks.
• Check the coolant level in the engine, if applicable. Inboard engines use a closed-loop cooling system with a reservoir of coolant, while outboard engines typically use an open-loop system that draws water from the surrounding body of water.
• If your boat has an inboard engine, you can check the temperature gauge, look for excessive smoke or steam, and feel the radiator hoses to determine their temperature. These indicators can help you assess if the thermostat is functioning properly.
• If you suspect an issue with the thermostat, you can remove it from the engine and perform a simple test. Place the thermostat in a clear jar and cover it with boiling water. Observe whether the thermostat opens as the wax inside expands due to the heat. A functioning thermostat should open at a specific temperature, typically between 50 and 60 degrees Celsius.
• If the thermostat does not open properly, it may need to be replaced. Consult a marine engine specialist or refer to the engine manufacturer's recommendations for further guidance.

By regularly checking and maintaining your boat's thermostat, you can help ensure optimal engine performance and prevent overheating issues while out on the water.

Flush the engine block

Flushing the engine block of a boat is an essential part of boat engine maintenance. It is especially important for ocean-bound boats as salt and minerals from seawater can enter the water circulation system and cause corrosive residues to build up on the inside of the engine block, exhaust components, water pump, and heat exchangers. This buildup can restrict water circulation and lead to engine overheating, which can cause fires and engine failure—a dangerous situation when out at sea.

To flush the engine block, follow these steps:

• Consult your boat's owner's manual to locate the cooling system components, including the raw water intake and flushing valve.
• Gather the necessary tools and supplies, including a garden hose that can reach your boat, a freshwater source, and valve adapters.
• Connect the hose to your boat's engine. The specific method of connection will depend on your engine type and may require additional attachments from a flush kit.
• Turn on the water supply and allow fresh water to flow through the engine's cooling system for several minutes.
• Check for proper water outflow by observing the water exiting the exhaust port. A steady and clear flow indicates a successful flush.
• It is recommended to flush your engine for 10 minutes after each use.
• If you are storing your boat for the winter, use antifreeze instead of water during the flushing process to prevent freeze-related engine damage.

By regularly flushing the engine block, you can prevent corrosion, improve engine performance, and extend the life of your boat's engine.

Check the water pump

The water pump is a crucial component of a boat's engine cooling system. It circulates water to cool the engine, and if it fails, the engine will overheat. To avoid this, it is important to regularly check the condition of the water pump and its key components, especially the impeller. Here is a step-by-step guide to checking your boat's water pump:

• Close the water inlet valve. This valve is usually located next to the water pump.
• Remove the pump cover. Unscrew and take off the cover. You may need to use a mallet to gently remove it if it is glued by the paper seal.
• Remove the paper seal. This seal is often torn and will need to be replaced, so keep a spare one handy.
• Take out the old impeller. Use two screwdrivers to carefully leverage and remove the impeller from the pump.
• Clean the pump. Scrape off any residue from the old seal using a cutter blade. Inspect the inside of the pump, the impeller, and the closing plate. Look for any cracks or damage. If the impeller fins remain flat due to prolonged immobilisation, they will need to be replaced.
• Grease the central axis and wet the fin tips. Before installing the new impeller, grease the central axis and wet the fin tips with soapy water or dishwashing liquid. This will prevent damage to the new impeller during the first few rotations.
• Reinstall the new impeller. Ensure the fins are facing the right direction by turning the wheel in the direction of the motor's rotation. Press the wheel firmly into the bottom of the housing.
• Replace the paper seal. You can use joint compound to ensure a perfect seal and prevent leaks.
• Reassemble the pump cover. Put the cover back on and tighten the bolts securely. This ensures a good fit and perfect tightness.
• Test the water pump. Open the water valve and start the motor. Check for any signs of leaks around the pump and the engine.

By following these steps, you can help ensure your boat's engine stays cool and prevent overheating. It is also advisable to carry a spare impeller on board at all times, as part of standard safety procedures.

Clean the heat exchanger

To cool down a boat engine, it is important to maintain the cooling system. One key component of this system is the heat exchanger, which needs to be cleaned regularly to prevent blockages and corrosion.

Cleaning the heat exchanger involves removing and descaling the component. This process can be done with various chemical solutions, such as Mary/Kate On & Off, RidLime, caustic soda, muriatic acid, or citric acid. It is important to wear protective gear when working with these chemicals and to be cautious of the type of metal in your heat exchanger, as some acids can damage certain metals. Commercial products like Rydlyme or Barnacle Buster are designed for this purpose and may be safer options.

To clean the heat exchanger, you can follow these steps:

• Remove the heat exchanger from the engine.
• Disassemble the heat exchanger if possible.
• Soak the heat exchanger in a chemical solution, diluted with water if necessary. Follow the manufacturer's instructions or recommendations from other boat owners for the appropriate concentration and duration.
• Rinse the heat exchanger thoroughly with fresh water. It may be beneficial to let it soak in a bucket of fresh water overnight to ensure all chemicals are removed.
• Reassemble the heat exchanger if necessary.
• Reinstall the heat exchanger in the engine.

It is recommended to clean the heat exchanger every 3 years, but this may vary depending on the manufacturer's guidelines and the condition of the component. Regular maintenance and inspection of the entire cooling system, including the heat exchanger, can help prevent issues and ensure the engine stays cool.

Check the raw water strainers

Raw water strainers are an essential component of a boat's cooling system. They are used to prevent grass, debris, and other solids from reaching the pump and causing blockages or damage. Here are some detailed instructions on checking and maintaining your raw water strainers:

Check for Blockages Regularly

It is important to regularly inspect your raw water strainer for any blockages or build-ups. After starting the engine, the first thing you should do is verify that water is flowing out of the exhaust line. Listen for a splashing sound, as this indicates that water is pumping out and your raw water strainer is clear. If the splashing sound stops, immediately shut down the motor and start troubleshooting. Open the sea strainer and check if water gushes out. If no water appears, you've found the blockage. Remove any debris or build-up from the strainer and the intake hose.

Clean the Strainer Basket

The strainer basket or filter should be cleaned regularly to ensure optimal performance. Depending on the frequency of use, a simple rinse of the screen or basket may be sufficient. However, if it hasn't been cleaned in a while, use a brush to remove any hardened deposits or build-up. Reassemble the strainer, making sure all gaskets seat properly, and check for leaks.

Choose the Right Strainer for Your Boat

When selecting a raw water strainer, consider factors such as hose size compatibility, flow rate requirements, and material durability in saltwater. The strainer should be made from durable materials such as bronze, plastic, or stainless steel. It should also be easy to clean and maintain, with removable filters or screens that can be accessed without tools.

Secure and Properly Install the Strainer

The raw water strainer must be securely fastened to a bulkhead, with the mounting location as close to the seacock as practical while allowing easy servicing. The hose connections from the seacock to the strainer and from the strainer to the pump should be as short and straight as possible. Use double hose clamps on both the seacock and the strainer for added security. Ensure that the seacock is connected to the inlet side of the strainer, which is usually identified by an arrow indicating the direction of flow.

Keep Spare Parts Handy

It is always a good idea to have spare parts on hand, such as strainer O-rings, raw water pump O-rings, and impellers. This will allow you to make quick repairs or replacements if needed and ensure that your boat's cooling system remains functional.

Frequently asked questions