Mr. Cool Resource Guide

How do you define raw water, fresh water, and zinc (sacrificial anode)?

Raw water

Sea water (colloquially known as lake water, raw water in the marine industry and “the surrounding water source” in technical documents) is what the boat is floating on regardless of its salinity. This is a term that seems to have gotten its start in the 70s and we’re unsure of the etymology. The older the boater, the more likely you are to hear this term.

Fresh water

Another term from the 70s, the term fresh water represents Antifreeze or glycol used in the engine. It’s the same thing that is used in your car engine to help transfer heat a little better and also to prevent corrosion of the radiator. Antifreeze is used in the same way for marine engines and can reduce engine temps near 5 degrees F in head to head studies. This has become much more common since GM changed to aluminum blocks and heads in some marine engines circa 2015. This keeps your engine block, heat exchanger, and possibly manifolds from seeing the corrosion effects of seawater reacting with aluminum engine components (heads , some exhaust components and sometimes engine blocks for some OEMs) which came about circa 2015 replacing the iron that is typically used for manifolds and risers.

Zinc (Sacrificial Anode)

A boat “zinc” is another colloquial term that we think started around the 1930s . This is likely because more often than not the metal used was zinc. So much like a copier was a Xerox back in the 70s, the term zinc became the common term for sacrificial anodes used on boats. Zincs were originally used as sacrificial anodes because the electro potential.

As we’ve become smarter these anodes are found in three primary metal types:

  • Zinc is used for salt water conditions
  • Aluminum is used for brackish water conditions
  • Magnesium is used for freshwater conditions.

The metals are changed based on the type of water because the electrolytes in the water transfer much better in salt water and scale down to the point that magnesium, which has a much higher electropotential protects the other metals on a boat much better in fresh water. They will oxidize before the other metals on the boat such as brass and copper in a state of corrosion and or electrolysis

For Fresh Water Cooling systems, what is the difference between a raw water cooled, half system and full system?


A Fresh water cooling system cools a marine engine protecting it from the seawater which will corrode the iron or aluminum block and possibly the manifolds. For the purposes of this answer, sea water (colloquially known as raw water in the marine industry) is what the boat is floating on regardless of its salinity. It is also known as the the surrounding water source. Antifreeze (colloquially known as fresh water) is circulated through the engine much like it would be in a car. The heat exchanger used to transfer the heat takes the place of a radiator in a car in this instance. It is a sacrificial element of the cooling system in a boat providing a barrier between the raw water and the engine’s water jacket and exhaust. Prior to 2015 most of the marine engines heads were made of cast iron including the exhaust and did not need a closed cooling system. The exception was the 496 CI which was always cooled because the water crossover was made of aluminum. Most intake manifolds for the marine industry had a brass insert in the cross over.

Marine engines for boats generally under 50 feet were raw water cooled (no heat exchanger using raw water to run through the engine block). This is because the engine metal could tolerate it a bit better but we still saw a great deal of corrosion of the water jacket and manifolds over time. The warmer it was and the higher the salinity the more corrosion existed eventually causing engines to be retired. But post 2015 nearly all marine engines use heat exchangers as the engine metal now used is more susceptible to corrosion.

Raw Water Cooled

A raw water cooled system means that seawater or lake water is used to cool the engine block. Most all of the marine engines used a belt drive water pump or a Impeller in the out drive to deliver water to the engine to be circulated in the engine by the circulating pump mounted on the engine. The circulating pump (water pump if it was on a car) pushes the raw water through the engine water jacket and then out through the thermostat housing on top of the engine. Using hoses this water is then split to each of the manifolds, passing through the manifold water jacket and then up through the risers (elbows) where it combines with the engine exhaust and goes back into the lake.

Half System or Block Only:

A half system is a partially closed system that uses both fresh water and raw water to cool the engine and exhaust components. A half system cools the block with fresh water and the manifold with raw water. It is more commonly used in brackish water. Raw water is drawn from the surrounding water source (such as an ocean or a lake) and circulated through the engine's heat exchanger. The block is then cooled by circulating antifreeze through the block and then using raw water as the cooling fluid for the heat exchanger. A hose commonly routes the raw water from the heat exchanger and then starts at the base of the exhaust manifold, working its way up through the exhaust components’ water jacket passing through the spacer, riser and elbow as applicable. The exhaust and the warmed seawater empties back into the surrounding water source.

Full System or Block and Manifold

A full fresh water cooling system is preferred in saltwater environments, as it helps to prevent corrosion of the engine block and manifolds.

The full system is a closed-loop system that circulates fresh water using the engine’s circulating pump (in a car this would be called the water pump) through the engine's water jacket and up through the thermostat housing. The heat generated by the engine is rejected into the antifreeze.

The heat exchanger is then used to transfer the heat from the fresh water to the raw water. The raw water is taken in either through an electric pump, outdrive or a belt driven pump and pumped through the heat exchanger. The raw water is circulated through the heat exchanger and used as the cooling fluid to keep the fresh water from getting too hot. The heat exchanger provides a barrier to keep the fluids apart and keep raw water from entering the engine’s water jacket. When the raw water leaves the heat exchanger, it goes into the riser elbow or spacer (depending on where the blocker plate was inserted) where it mixes with the exhaust gas and both then go back into the surrounding water source.

There are 2 primary differences between a half and full system.

In a full system the pump circulates glycol through the exhaust manifold. There is a blocker plate between the manifold and spacer or riser or elbow in a full system. In a full system this keeps the glycol from exiting through the riser. In a half system, glycol is only circulated through the engine block.

The heat exchanger is larger in a full system as it needs to handle the increased heat held by the exhaust manifolds. Fresh water continues circulating between the engine’s water jacket and the exhaust manifolds while continually being cooled by the heat exchanger. In a full system the raw water exiting the heat exchanger will pass through a hose to the base of the spacer, riser or elbow as applicable and combines with the exhaust going back into the surrounding water source.


A full system or full fresh water cooling system provides better protection against corrosion for the block and manifolds and is recommended for boats that operate in saltwater environments. These systems require a heat exchanger commonly 50% larger than a half system due to the heat load from the manifolds on the cooling system. These systems maintain a more stable environment for the engine which makes just about everything work better including the electronics and alarms.

A half system uses fresh water to cool the block and cools the exhaust system with raw water, offering no protection for the manifolds. This type of cooling system was used more often prior to 2015. In our current marine era more engines are coming from the OEMs with full systems.

A Raw Water cooled system for engines prior to 2015 works pretty well if the surrounding water source has little or no salinity. This system design takes the raw water from the surrounding water source and is pumped through the engine water jacket out of the thermostat housing and into the bottom of the manifolds where it subsequently combines with the exhaust gases leaving the engine through the risers and reentering the surrounding water source. This system if in salt water will quickly corrode your engine block, manifolds and risers. As an example, in South Florida in the US on the gulf side of the peninsula you can look for your exhaust to last between 3 and 5 years depending on your usage. By that time your block will have significant corrosion.

What is the difference between a marine heat exchanger and a marine oil cooler ?

Both heat exchangers and oil coolers are components used in marine cooling systems, but they serve different purposes and operate under different conditions.

A heat exchanger is a device that transfers heat from one fluid to another without the fluids mixing. In a boat engine, the heat exchanger is used to transfer heat from the engine's coolant to the raw water that is circulated through the engine's cooling system. The raw water absorbs the heat and is then discharged back into the water. This process allows the engine to maintain a stable operating temperature and prevents overheating. Heat exchangers are typically made of materials that are resistant to corrosion, such as copper or stainless steel.

An oil cooler is also a component that transfers heat from one fluid to another without the fluids mixing. Generally these are designed to cool the engine oil, transmission or gear oil, fuel, hydraulic fluid or power steering. It operates by circulating the oil around a series of fins or tubes while raw water runs through the tubes. It is always this way probably because the raw water is not nearly as clean of a fluid as the lube fluids. The cooled oil is then returned to do it’s job. The purpose of an engine oil cooler is to prevent overheating, which can cause the oil to break down and lose its lubricating properties. This is also true for the power steering and transmission coolers. Fuel is cooled to prevent vapor lock and also to increase the fuel density in turn increasing the fuel package delivered to the cylinder increasing horsepower and more complete use of the fuel package delivered. Oil coolers are typically made of materials that are resistant to corrosion such as copper and brass in the marine industry. In summary a heat exchanger and oil cooler are made in much the same manner. They are used in slightly differing circumstances. A heat exchanger is used to transfer heat from the engine coolant to raw water, while an oil cooler is used to cool the engine ‘s various types of oil. Both components play important roles in keeping the engine operating at a safe and optimal temperature commonly around 177F.

What is the difference between raw water and fresh water?

In a marine cooling system, the terms "raw water" and "fresh water" refer to two different sources of fluids used to cool the engine.

Raw water is water that is drawn directly from the surrounding environment, such as a lake, river, or ocean. This water is typically used as a cooling medium to remove heat from the engine, and then discharged back into the environment. Raw water can contain a variety of impurities, such as salt, sand, and debris, which can cause corrosion and damage to the engine if not properly treated or filtered inbound to the heat exchanger.

“Fresh water” is a colloquial term in the marine industry for glycol or antifreeze. This “Fresh water”is typically used in a closed-loop system, where it circulates through a heat exchanger and the engine to remove heat from the engine, and then continues to circulate. This system is commonly used in stern drive and inboard or inboard/outboard applications. It is preferred in saltwater environments, as it helps to prevent corrosion of the engine.

In summary, raw water is water taken from the environment and used to cool the engine, while “fresh water” is a marine industry term for glycol/antifreeze.

What are the causes of electrolysis on a marine heat exchanger?

Electrolysis is a phenomenon that occurs in boats and other metal structures that are exposed to water. It is the process by which electric current flows through a conductive medium and causes metal ions to dissolve, resulting in corrosion and damage to the metal structure. Galvanic reactions are also technically electrolysis but discussed separately in this document. Electrolysis is the process of deplating a high density condition (in this case a heat exchanger) to a lower density condition (the surrounding water source) as the charge in the water causes the copper molecules of the heat exchanger to release and move into the solution that we refer to as raw water or seawater.

Stray electrical currents can be generated by a number of sources on a boat, such as improperly grounded electrical systems or damaged wiring. If these currents flow through the cooling water, they can cause electrolysis and corrode the heat exchanger. A well grounded boat can keep the electrolysis at bay when tied to the earth usually at the charging station. Someone leaving their charging lines in the water (particularly if they have cracked plastic coatings) is the primary example of how the water is charged. This begins the process of electrolysis on a boat.

Electrolysis is a chemical process that occurs when an electric current flows through a conductive medium and causes a chemical reaction to occur. In the case of boats, electrolysis occurs when the metal parts of the boat are exposed to water that contains electrically conductive materials, such as dissolved salts and minerals. It is most aggressive when there is an electrical charge in the water.

It can happen either internally (invisible to the user) causing a leak, most commonly at the tube bundle header; but, also shows itself by creating holes in the bundle tubes.

It can show itself externally which looks like common corrosion. This is the fault of your grounding system and is not influenced by the construction of the heat exchanger.

When these conductive materials (electrolytes or salty water) come into contact with the metal parts of the boat, they create a conductive pathway that allows electric current to flow. This current causes metal ions to dissolve, resulting in what appears to be corrosion and damage to the metal parts of the boat. It is actually depleting of the metal in the water which detaches it from the coatings and (in most cases) the heat exchanger looks corroded. The chemical reaction that occurs during electrolysis can be summarized as follows:

At the anode (positive electrode): The metal at the anode dissolves and becomes ionized, releasing electrons into the solution. For example, if the anode is made of zinc, the following reaction will occur:

Zn → Zn2+ + 2e-

At the cathode (negative electrode): Electrons from the anode combine with positive ions in the solution, causing the metal to plate out on the cathode. For example, if the cathode is made of copper, the following reaction will occur:

Cu2+ + 2e- → Cu

Overall reaction: The net result of this chemical reaction is the dissolution of metal at the anode (the heat exchanger has become the anode) and the deposition of metal on the cathode (which is the seawater). This process can result in the depletion of metal from the anode and the accumulation of metal on the cathode, which can cause corrosion and damage to the metal parts of the boat.

In a boat, electrolysis occurs when the metal parts of the boat (such as the engine, propeller, and other metal fittings) are exposed to water that contains electrically conductive materials. These materials can include dissolved salts and minerals, stray current from nearby boats or electrical sources, and other conductive materials that may be present in the water. When these conductive materials come into contact with the metal parts of the boat, they create a conductive pathway that allows electric current to flow. This current causes metal ions to dissolve, resulting in corrosion and damage to the metal parts of the boat.

To prevent electrolysis from occurring, it is important to take several steps, such as using sacrificial anodes made of a more active metal, avoiding dissimilar metals, properly grounding the electrical system, and performing regular maintenance. These steps can help to minimize the occurrence of electric current and prevent the chemical reactions that cause electrolysis from taking place.

What is the difference between plating and deplating?

Plating and deplating are two opposite processes that involve the transfer of metal ions between a solution and a substrate. The main difference between plating and deplating is the direction of the transfer. Plating refers to the process of depositing metal ions onto a substrate to form a thin, even layer of metal. This process is also known as electrodeposition, and it is commonly used to improve the appearance, wear resistance, and corrosion resistance of metal parts. Plating is achieved by passing an electric current through a solution that contains dissolved metal ions, and placing the substrate to be plated (e.g., a metal part) in the solution as the cathode (negative electrode). As a result of the electric current, the metal ions in the solution are attracted to the cathode and are reduced to form a solid metal layer on the surface of the substrate. The metal layer adheres to the substrate through a combination of electrostatic forces and chemical bonding, resulting in a durable and uniform coating.

Deplating refers to the process of removing metal ions from a substrate and dissolving them into a solution. This process is also known as corrosion or dissolution, and it is the result of chemical reactions that occur when metal parts are exposed to corrosive environments, such as seawater. Deplating can occur in two ways: through chemical reactions that directly dissolve metal ions from the substrate (e.g., metal ionization), or through electrochemical reactions that involve the transfer of electrons between the substrate and the surrounding environment (e.g., electrolysis). In either case, the metal ions that are dissolved into the solution can be carried away by the fluid flow and cause further corrosion or damage to other metal parts that they come into contact with.

In summary, plating involves the deposition of metal ions onto a substrate to form a protective layer, while deplating involves the removal of metal ions from a substrate and dissolution into a solution, which can lead to corrosion and damage of metal parts.

What are some of the things that enable electrolysis?

Impurities in the cooling water

Impurities in the cooling water, such as salts, minerals, and organic matter, can increase its electrical conductivity enabling electrolysis. These impurities can come from a variety of sources, such as saltwater / seawater or sometimes even freshwater sources.

Poorly operating cathodic protection systems

Cathodic protection systems are used to protect metal components on a boat from corrosion by providing a more easily corroded "sacrificial" metal that corrodes first. However, if the cathodic protection system is not properly installed or maintained, it can cause electrolysis and corrode the heat exchanger.

Dissimilar metals: A galvanic reaction is another kind of electrolysis. If different types of metals are used in the heat exchanger, such as copper and aluminum, they can create a galvanic cell when they come into contact with the cooling water. We find that in the marine industry that this is often accompanied by a small leak in salt water. The salt water then bridges the two metals and creates a path through which the corrosion can feed between the salt and stray currents.

This cell generates an electric current, which causes metal ions to dissolve into the surrounding water source (deplate) and corrode the heat exchanger (remove metal from the heat exchanger and flow those small molecules into the surrounding water source). Although technically this is electrolysis, it’s more commonly recognized as corrosion by the user. It is common when there is a brass header and an aluminum body. As soon as a salt bridge is built across the two components they will become one and corrode each other.

How do you prevent electrolysis?

To prevent electrolysis from occurring in a marine heat exchanger, it is important to use the correct type of metals, properly ground the electrical system, and perform regular maintenance. Additionally, using sacrificial anodes made of a more active metal can help protect the heat exchanger from corrosion. There are also things that happen chemically during electrolysis. To prevent electrolysis from occurring in a boat, it is important to take several steps that may include:

Using sacrificial anodes: Sacrificial anodes are made of a metal that is more electrically active than the metal parts of the boat. When the boat is in the water, the anodes will corrode instead of the boat's metal parts, protecting them from electrolysis. Avoiding dissimilar metals: Whenever possible, it is best to avoid using dissimilar metals in the same location on a boat. If this is not possible, it is important to ensure that the metals are electrically isolated from each other.

Properly grounding the electrical system: A boat's electrical system should be properly grounded to prevent stray current from flowing through the metal parts of the boat.

Regular maintenance: Regular maintenance of a boat's electrical system and metal parts can help to prevent electrolysis from occurring. This includes cleaning and inspecting the boat's metal parts and replacing sacrificial anodes when necessary. In conclusion, electrolysis is a common problem in boats that can cause corrosion and damage to the metal parts of the boat. It is caused by electric current flowing through a conductive medium and dissolving metal ions. To prevent electrolysis from occurring, it is important to use sacrificial anodes, avoid dissimilar metals, properly ground the electrical system, and perform regular maintenance.

What are the environmental factors that cause electrolysis?

Saltwater environments: Boats that operate in saltwater environments are more prone to electrolysis than those that operate in freshwater environments. This is because saltwater is a more conductive medium than freshwater, which means that it is more likely to create a conductive pathway for electric current to flow.

Stray current: Stray current is an electrical current that flows through the water and can be caused by nearby boats, marinas, or other electrical sources. When this current comes into contact with the metal parts of a boat, it can cause electrolysis to occur.

Dissimilar metals: When two different types of metal come into contact with each other in the presence of an electrolyte (such as water), a small electric current can be generated. This current can cause corrosion and damage to the metal parts of the boat. Poor grounding: If a boat's electrical system is not properly grounded, it can create a pathway for stray current to flow through the boat's metal parts, which can cause electrolysis to occur.

Impurities in the water: Water that contains impurities such as dirt, sand, and other minerals can increase its conductivity and create a pathway for electric current to flow.

How often should I change my zinc anode?

Sacrificial anode maintenance is tough to predict. A good way to determine the maintenance schedule for a zinc is to look at it every time you use the boat for the first 10 times of use. Note the condition of the anode and how it changes over time and then create your own replacement schedule. It seems like a bit of work but if you’re noticing the anode is being eaten away from corrosion you could be in a situation where you have a charge in the water near your boat. It is a tell-tale sign of the conditions of the surrounding water source. If there is a charge in the water nearby, this could cause electrolysis which can eat up your new heat exchanger or oil cooler very quickly. If the anode is 50 percent gone it should be replaced is a common rule.

How long will a new heat exchanger or oil cooler last?

This question is impossible to answer with one sentence because it is dependent upon the environment the boat is in, specifically the surrounding water source salinity, local temperatures, how the boat is stored and the effort put into cleaning the boat up after each use. In the great lakes, a heat exchanger can last 25 years or more. We see Chris Craft Heat exchangers from the 70s still in use and going strong. That’s a combination of low seasonal usage and weather and lack of salinity. All things equivalent, the same boat on the gulf side of Florida will last around 5 to 8 years. On the Atlantic side you’ll get a slightly longer life. In Indonesia where the water can rise to 108 degrees F and salinity is high and outside temperature is high you can simply cycle through them. Particularly in saltwater conditions, if you flush your engine’s seawater system after each use, that will extend the life of your engine more than any other action you can take. Heat exchangers can corrode, erode from constant use (e.g generator heat exchangers to keep boats cool at the docks where electric supply is limited), and they can have electrolysis problems due to bad grounding. We have customers from the Bahamas that change their generator heat exchangers annually to preclude failure. It is not always tied to the number of hours used.

Can you tell me if my heat exchanger is good or bad?

It would be difficult for anyone to tell how good a heat exchanger is. Telling you if one is bad is much easier (e.g. if it leaks or exhibits corrosion, erosion or electrolysis characteristics). After the part has been used, there is no easy way to see if you have electrolysis inside of the cooling tubes. You cannot logically weigh the part to determine the amount of metal loss. . You cannot visually determine the condition of the cooling tubes even when gun sighting the heat exchanger. The only thing you realistically can do is to use a cleaning solution to remove the scale and see if you’re happy with the visual condition after removing the end caps. This is a crap shoot.

This is why reviewing anodes on a regular basis is so important. If the anode is being eaten away by the surrounding water source and you catch it early you can keep your heat exchanger or oil cooler in good condition.

This is also why buying a used heat exchanger is seldom a great idea. Regardless of the good intentions of the seller, cleaning up a used heat exchanger and painting the outside will only make it look good on the outside. But the business end of a heat exchanger is on the inside. And we know of no good way of determining how good a heat exchanger is from any inspection that we’re aware of. You can only say that at the time of testing that it didn’t leak. Repaired heat exchangers seldom have a warranty. And this is likely why.

In the early days we would repair products but soon found out that’s a very bad idea. You cannot comfortably know if a heat exchanger will fail after a cooling bundle tube repair as an example. The tube right next to the one that corroded through saw nearly the exact same environmental conditions as the one you just repaired. It’s illogical to think it’s not on the verge of failure also. And we found that fixing a product that was old and plugging leaking cooling tubes was just putting our finger in the exploding dike so to speak. We always saw them again and again until the customer became frustrated and a new one was purchased. Also the cost of a repair is often as much as 30% the cost of a new replacement product. It just doesn’t make sense to us so we quit doing repairs. This is also why we don’t sell used products of any kind.

If I find a heat exchanger or oil cooler that is the same size as the one I have can I replace it?

A heat exchanger or oil cooler is not made on the outside. Its made on the inside. We’ve seen sites and old salts with a great deal of experience that say that an oil cooler size is all that matters. That’s really an uninformed answer completely untrue. Heat transfer is based on three things primarily:

Surface area of the cooling tubes (so if the size is the same this cooling area would most often be much the same). Differential between the cooling fluid and the fluid being cooled (these are environmental circumstances and not related to the cooling device so these remain the same).

Fluid speed of the hot and cold fluid. This is the most important of the three as you can change the amount of cooling you will get by increasing the fluid speed up to the point of erosion. We’ve done this on test boats with engineers and by simply increasing the speed of your fluid pumps you will increase the efficiency of the cooler, dropping the temperature of the engine oil or other cooling fluid.

Fluid speeds can be increased by changing the fluid speed via the pump and also by changing what is called ‘baffling’ on the inside of the cooler. The number of the baffles and how much of the bundle they cover has everything to do with the fluid speed inside of the cooler and therefore significantly impacts proper cooling. In all cases where it is reasonable a responsible aftermarket source would obtain the OEM unit they intend to replace and evaluate the inside of the cooler, duplicating it with much attention to dimensional accuracy so that the fluid speeds and backpressure remain the same.

The term backpressure is another colloquial term in many industries for fluid resistance to movement or fluid friction. Technically there is no such thing as backpressure. It is commonly an increase in pressure due to an incorrectly made cooler or a cooler being used in an unintended way. If you’re measuring the pressure between the pump and the cooler, an incorrectly baffled cooler will have increased pressure which can harm the pumping mechanism. If it has decreased pressure that means that the fluid speed may have decreased to the point where the cooler cannot do its job. And your engine temperatures will tell you if that’s the case.

And here’s the rub: sometimes these standard or same size coolers work just fine when installed. The damage to the pump happens over time and it may be the person you sell your boat to that has to deal with the issue. Standard oil coolers have standard baffling and more frequently than not they are intended to be used as a replacement for an OEM cooler in most cases. They are an emergency replacement or some other interim fix. If someone is trying to sell you a non engineered cooler because they say they know better, you may regret the decision to allow them to proceed. Engineers who work in heat transfer are often very precise in their expectations. Heat transfer is a specialty in mechanical engineering and developing cooling devices is their job. Make sure your cooler is being replaced with an equivalent device.

What is the purpose of a water strainer in a marine cooling system?

The purpose of a water strainer in a marine cooling system is to filter out any debris or foreign material that may be present in the water before it enters the cooling system. Marine engines that use seawater to cool the engine would have potential failures if the water wasn’t somewhat without debris. Also strainers remove eel grass and other types of marine materials. If debris is allowed to enter the cooling system, it can cause damage to the engine or cooling system components, reducing their lifespan or efficiency. The debris could also block the inbound water supply which could cause the engine to very quickly overheat.

The water strainer is usually installed in the seawater intake line, between the hull of the boat and the raw water pump. It typically consists of a removable filter basket or mesh screen that catches debris such as seaweed, shells, or sand particles, preventing them from entering the cooling system. The filter basket needs to be cleaned or replaced periodically to ensure that it continues to function properly.

In summary, a water strainer in a marine cooling system is a crucial component that protects the engine and cooling system from damage by filtering out any debris or foreign material that may be present in the water.

What are the benefits of using a closed cooling system in a boat engine?

Engine block erosion is the biggest reason to do this. Does aluminum corrode in saltwater? Yes, it sure can. We're talking about galvanic corrosion. Back in science class you'd say that this is where one metal in an electrically conductive solution (such as salt water) gives up atoms when connected to a dissimilar metal in that same solution. As of 2015 some marine manufacturers switched from iron to aluminum in some of their engine components so the protection of the blocks and heads is imperative if you have a post 2015 engine. Iron does better but is still a problem. All you need to do is place a piece of iron in a glass in saltwater and leave it on your kitchen table for a week. It will give you an idea of what is going to happen. Closed cooling on a marine engine is always a good idea.

Protection against other means of corrosion: A closed cooling system can help protect the engine from corrosion. This is because the coolant in a closed system is not exposed to outside air or water, which can contain contaminants that cause corrosion. A closed cooling system uses coolant to transfer heat from the engine to the heat exchanger, rather than seawater. This eliminates the possibility of saltwater corrosion within the engine block, exhaust manifold, and other internal components. This reduces the build-up of aquatic material including plant and animal residue, salt, debris and mineral deposits within the water jacket of the engine block and exhaust system.

Extended engine life: A closed cooling system can help extend the life of the engine by reducing the wear and tear on the engine components. This is because the engine is less likely to see sea water reducing corrosion not only in the engine block but also in the manifolds which marginally helps reduce scale in the exhaust ports.

Reduced maintenance: With a closed cooling system, there is less maintenance required than with an open system. This is because there is no need to flush the engine with fresh water after every use, which can save time and money.

Subtle improvements in engine performance: By maintaining a consistent temperature, a closed cooling system can help to optimize engine performance. The engine is less likely to overheat, which can lead to problems like engine damage and reduced fuel efficiency.

How does a water pump work in a marine cooling system?

This answer is primarily centered around the block used by Mercruiser Volvo Crusader and some others. There are two water pumps on a marine system.

One pump circulates the glycol or antifreeze or fresh water through the engine block’s water jacket and possibly the manifolds depending on what closed cooling system is being used.

The other water pump is for moving the seawater through the raw water circuits in either the heat exchanger and exhaust above the manifold. Or, it’s the pump for circulating raw water throughout the engine jacket and exhaust. Again it depends on the closed cooling system type you’re using.

Please see definitions for raw water and fresh water in relation to a marine cooling system. In a marine cooling system, the circulating pump (what we call a water pump on a car) is responsible for circulating the coolant (fresh water or antifreeze) through the engine to absorb heat, and then through a heat exchanger where it is cooled by seawater before returning to the engine.

The water pump is typically driven by a belt connected to the engine's crankshaft, and its impeller is housed in a housing known as a "pump body." As the impeller rotates, it creates suction that draws coolant into the pump body through an inlet port. The impeller blades then force the coolant through the pump body and out through a discharge port, where it is directed into the engine's cooling passages.

One important consideration in marine cooling system design is the need to prevent seawater from entering the engine itself. This is typically accomplished through the use of a heat exchanger, which separates the engine's coolant from the seawater used to cool it. In a typical heat exchanger design, seawater is pumped through a separate set of tubes or passages that run parallel to the engine's cooling passages, allowing heat to transfer from the engine coolant to the seawater without the two fluids mixing.

What is the role of antifreeze in a boat's freshwater cooling system?

To keep the engine block from getting seawater in it when a closed cooling system is used. The antifreeze will circulate using the water pump or circulating pump and go through one circuit of your heat exchanger. The only component that should see seawater in this case is the heat exchanger, which is an expensive but unfortunate sacrificial component on a marine engine so that the block (half system) or block and manifolds (full system) don’t experience corrosion from the surrounding water source.

How does a marine cooling system affect engine performance?

There are some marginal improvements from an engine’s performance when closed cooling is used. Don’t expect to see a 10% increase in horsepower. But it will keep your engine in a steadier state of operation overall. In virtually all cases it’s better for your engine’s long term health.

What are the signs that your boat's cooling system may be failing?

The temperature gage is your first indicator. The second is when you see an oil slick coming out of the exhaust of the boat. Both of these are failure notifications. If you’re buying a new boat and there’s an oil slick, it’s a problem. Coming from where is the real issue. But it’s either a leaking port in the engine, leaking cooler, leaking exhaust, and the list continues. It’s smartest to change our your oil coolers and exhaust components on a reasonably regular interval. As environmental conditions change based on your location on this globe, you’ll be best served to establish a relationship with a competent marine mechanic who will keep your boat running well. Fixing a broken boat is much more expensive than maintaining it.

What are the steps to troubleshoot an overheating issue on an oil cooler on a boat?

The following are the general steps to troubleshoot an overheating issue on an oil cooler on a boat:

Check for blockages: A common cause of overheating in oil coolers is blockages in the seawater supply. Check in for blockages in the inbound water or grass or debris in the strainer.

Check for water pump issues: The water pump (which may be electric or mechanical) is responsible for circulating water through the cooling system. Check for issues such as a faulty impeller, worn bearings, or loose belts that can prevent the water pump from working properly. Worn impellers reduce the fluid speed and can cause an increase from 190 to 210. Faulty or broken impellers can have a more drastic impact on the boat’s engine operating temperature.

Check for clogs in the heat exchanger water passage. Follow from the strainer to the heat exchanger to determine where the inbound seawater port is. The heat exchanger is responsible for transferring heat from the coolant (hot side) to the seawater (cool side). If there are any clogs or blockages in the heat exchanger, it can cause the oil to overheat. Check the heat exchanger seawater circuit for any debris or sediment buildup that can clog the tubes. You can also remove the inbound seawater hose to see if there is sufficient water coming to the engine.

Check for insufficient coolant levels: Low coolant levels can cause the engine’s fluids to overheat. Check the coolant levels and top up as needed.

Check for thermostat issues: A faulty thermostat can cause the engine to overheat forcing the antifreeze / glycol through the overflow port of the thermostat housing. Check the thermostat for proper operation by removing the thermostat housing and test for proper operation.

Check the cooling device for damage: If none of the above steps resolves the issue, it may be necessary to remove the oil cooler from the boat and inspect it for any signs of damage or wear.

Seek professional assistance: If the issue persists, it is best to seek the assistance of a qualified marine mechanic to diagnose and repair the issue.

What is the difference between a keel-cooled and a heat exchanger-cooled marine engine?

In a keel-cooled system, the engine's coolant flows through a series of pipes or sometimes an aluminum block attached to the outside of the boat's hull, typically running along the keel where it is always in the water even when underway. The hull acts as a heat sink, allowing the surrounding water to absorb the heat generated by the engine. The cooled coolant is then recirculated through the engine. Because fluid speed increases generally improve the efficiency of a cooling system the faster the boat is driven, the better the cooling, which is good because the engine is generating more heat!

In a heat exchanger-cooled system, the engine's coolant flows through a heat exchanger, which is essentially a device that transfers heat from one fluid to another without the fluids coming into direct contact. The engine's coolant is circulated through the heat exchanger, and a separate circuit of seawater is pumped through the heat exchanger to absorb the heat from the coolant. The heated seawater is then discharged back into the ocean.

The greatest benefit to a keel cooling system is they do not get plugged up as the port sizes are frequently generous. They are typically less expensive and simpler to install, but generally are not very efficient at cooling the engine as would be a heat exchanger-cooled system. Heat exchanger-cooled systems are generally more complex and expensive, but are often preferred for higher performance or larger engines, as they provide more consistent cooling and are less affected by changes in seawater temperature. Keel coolers are frequently found on sailboats where engines sizes of 15hp are frequently found.

What are the advantages and disadvantages of using a raw water cooling system on a boat?

If this boat’s engine was manufactured of aluminum there is no up side unless you live where only pristine water exists. Otherwise your engine is going to corrode, eventually leak and subsequently become a very large paper weight.

How does a marine exhaust system work and how is it related to the cooling system?

A marine exhaust system is responsible for removing the engine's exhaust gases and discharging them safely overboard. In most cases, a marine exhaust system works by directing exhaust gases from the engine through a series of pipes and components until they exit the boat through the exhaust outlet.The gases frequently go directly into the water with the cooling fluid used for the engine. The exhaust system is related to the cooling system because some components of the exhaust system are cooled by the engine's cooling system. For example, the exhaust manifold is a component that is responsible for collecting exhaust gases from each cylinder of the engine and directing them through the exhaust system. In some marine engines, the exhaust manifold is cooled by the engine's freshwater cooling system. This is known as a "freshwater cooled" exhaust system. In this case the antifreeze or coolant is recirculated through the engine. There is a blocker plate that exists between the manifold and the components above the manifold referred to as a spacer, elbow or riser. These three components will receive seawater to run through their water jackets / cooling ports and the seawater will combine with the exhaust to some degree and then exit with the exhaust gases into the surrounding water source.

In other marine engines made prior to 2015, the exhaust manifold is cooled by seawater that is drawn into the exhaust system through a raw water pump. This is known as a "raw water cooled" exhaust system. In this type of system, seawater is pushed into the manifold and then the seawater continues as described above into the manifold, spacer, elbow and or riser the seawater will combine with the exhaust to some degree and then exit with the exhaust gases into the surrounding water source. Regardless of whether the exhaust system is freshwater or raw water cooled, it is an important component of the overall cooling system of the marine engine. Blockages in ports of the exhaust (commonly from scale due to oxidation) can easily cause damage to the engine and potentially even cause it to overheat. Therefore, it is important to maintain and inspect the exhaust system regularly to ensure that it is in good working order.

What is the effect of saltwater on a boat's cooling system and how can it be mitigated?

Saltwater can cause corrosion and scaling in a boat's cooling system, which can reduce its effectiveness over time. Corrosion can occur due to the saltwater's corrosive properties and can lead to leaks and other damage to the cooling system components. Scaling, on the other hand, can occur due to the minerals in the saltwater and can clog the cooling system passages, reducing water flow and increasing the risk of overheating.

To mitigate the effects of saltwater on a boat's cooling system, several steps can be taken, including:

Flushing the system: After every use in saltwater, the cooling system should be flushed with fresh water to remove any salt and mineral deposits that may have accumulated. This helps to prevent scaling and corrosion in the system.

Use of sacrificial anodes: the use of sacrificial anodes can protect the cooling system components from corrosion by sacrificing themselves instead of the metal components. Make sure you’re using the right metal for the right water salinity. Anti-scaling agents: The use of anti-scaling agents can help prevent mineral buildup in the cooling system.

Use of corrosion inhibitors: Corrosion inhibitors can be added to the cooling system to help prevent corrosion of the metal components.

Regular maintenance: Regular maintenance of the cooling system, including inspection of hoses, clamps, and other components, can help prevent leaks and ensure proper functioning of the system.

What is the ideal operating temperature range for a boat's cooling system and what are the consequences of operating outside that range?

The normal operating temperature for a 5.7L GM engine that’s been marinized by one of the major OEMs (Mercruiser or Volvo as examples) is typically between 160 and 175 degrees Fahrenheit (71 to 79 degrees Celsius). In general water temp should not go above 170 on EFI engines and not much above 160 on carb engines. Higher temps can cause corrosion to start building up in the exhaust system.

Exact operating temperatures can vary depending on several factors, including the specific engine model, the boat's operating conditions, and the type of cooling system used. It is important to consult the manufacturer's guidelines for the specific engine to determine the recommended operating temperature range. Temperatures from 190F up to the engine’s over temp alarm should make you nervous. The over temp alarm for a 5.7L GM marinized engine typically sounds when the engine's temperature rises above 220-240°F (104-116°C). You should act in accordance with your owners manual if these alarms go off.

Continuing to operate the engine at this temperature can lead to various risks, including engine damage, reduced engine performance, and potential on boat safety hazards due to the engine overheating. If the over temp alarm sounds, it is recommended to evaluate your safety conditions and then shut down the engine posting the appropriate notifications for a stranded boat and then operate in those conditions while you determine whether its logical to investigate the cause of the overheating issue or consider a tow. This is opinion. Always operate in accordance with instructions from the OEM manufacturers.

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