Answer
Apr 14, 2023 - 04:56 AM
Introduction:
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.
Summary
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.
©2023 Mr. Cool Marine LLC
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.
Summary
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.
©2023 Mr. Cool Marine LLC
