Answer
Apr 07, 2023 - 02:58 PM
Introduction:
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 the surrounding water source. Antifreeze (colloquially known as fresh water in the marine industry) 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. Prior to 2015 in the mercruiser brand more engines were raw water cooled (no heat exchanger) because the engine metal could tolerate it better, 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. The seawater is brought in through an electric pump or out drive. Most often it is delivered to the circulating pump on the engine ( water pump if it was on a car) which pushes the fluid 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 fresh water cooling system for a boat is a partially closed system that uses both fresh water and raw water to cool the engine. Raw water is drawn from the surrounding water source (such as the ocean or a lake) and circulated through the engine's heat exchanger. The seawater is used as the cooling fluid in a heat exchanger. The block is then cooled by circulating antifreeze through the block and then using seawater as the cooling fluid for the heat exchanger. Then the warmed seawater passes through the manifolds and risers cooling them as it goes. A hose commonly routes the seawater from the heat exchanger and then starts at the base of the exhaust manifold, working its way up through the water jacket of the riser mixing with the engine’s exhaust. Both the exhaust and the warmed seawater empties back into the sea.
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. A full fresh water cooling system for a boat uses a closed-loop system that circulates antifreeze (fresh water) using the engine’s circulating pump (in a car this would be called the water pump) through the engine's water jacket. This removes heat generated by the engine as it is rejected into the antifreeze. The heat exchanger is used to transfer the heat from the antifreeze to the seawater. Raw water is drawn from the surrounding water source (such as the ocean or a lake) and circulated through the engine's heat exchanger. The seawater is used as the cooling fluid in a heat exchanger. The seawater is taken in either through an electric pump, outdrive and pumped through the heat exchanger.
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.
a half system uses antifreeze to cool the block and offers no protection for the manifolds used primarily prior to 2015.
A Raw Water cooled system for engines prior to 2015 works pretty well if the surrounding water source has no salinity.
©2023 Mr. Cool Marine LLC
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 the surrounding water source. Antifreeze (colloquially known as fresh water in the marine industry) 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. Prior to 2015 in the mercruiser brand more engines were raw water cooled (no heat exchanger) because the engine metal could tolerate it better, 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. The seawater is brought in through an electric pump or out drive. Most often it is delivered to the circulating pump on the engine ( water pump if it was on a car) which pushes the fluid 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 fresh water cooling system for a boat is a partially closed system that uses both fresh water and raw water to cool the engine. Raw water is drawn from the surrounding water source (such as the ocean or a lake) and circulated through the engine's heat exchanger. The seawater is used as the cooling fluid in a heat exchanger. The block is then cooled by circulating antifreeze through the block and then using seawater as the cooling fluid for the heat exchanger. Then the warmed seawater passes through the manifolds and risers cooling them as it goes. A hose commonly routes the seawater from the heat exchanger and then starts at the base of the exhaust manifold, working its way up through the water jacket of the riser mixing with the engine’s exhaust. Both the exhaust and the warmed seawater empties back into the sea.
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. A full fresh water cooling system for a boat uses a closed-loop system that circulates antifreeze (fresh water) using the engine’s circulating pump (in a car this would be called the water pump) through the engine's water jacket. This removes heat generated by the engine as it is rejected into the antifreeze. The heat exchanger is used to transfer the heat from the antifreeze to the seawater. Raw water is drawn from the surrounding water source (such as the ocean or a lake) and circulated through the engine's heat exchanger. The seawater is used as the cooling fluid in a heat exchanger. The seawater is taken in either through an electric pump, outdrive and pumped through the heat exchanger.
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.
a half system uses antifreeze to cool the block and offers no protection for the manifolds used primarily prior to 2015.
A Raw Water cooled system for engines prior to 2015 works pretty well if the surrounding water source has no salinity.
©2023 Mr. Cool Marine LLC
