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Marine Cooling Systems and

Heat Exchangers

Marine engines, as well as automotive engines are, cooled by circulating water thruthe engine block. Marine engines are unique in that there are two different tyes of

cooling systems. !he standard raw water system, and the fresh water "commonly

known as the closed# cooling system.

Raw Water Cooling Systems

$aw water cooling systems draw water from outside the boat "seawater or lake water#.%ater is umed from the source to the engine block then the engine circulation um

forces the raw water thru the engine block and the water is exelled thru the exhaust.

$aw water cooling systems are relatively simle and the standard cooling system on

most Marine Engines. !he raw water um in most cases is inside the outdrive. &n

larger engines and inboard engines the raw water um is located inside the boat and

is driven by a v'belt or directly off of the crankshaft. !here are hidden dangers that

can accumulate over time causing you to send big (ollars on reairs. !he danger is

using salt water as a coolant in your engine. Salt water can be highly corrosive.

$unning salt water through your engine block and exhaust manifolds will lead to

destructive corrosion that is unseen until your engine or exhaust manifolds fail.

)enerally seaking, marine engines cooled with raw water, esecially ones that use

salt water, have a shorter life san than marine engines cooled with a closed cooling

system.

Fresh Water Systems with Heat Exchangers and Keel

Cooled systems

*resh water cooling systems, also known as a closed cooling systems, come in several

varieties. !he most common tye utili+es a Heat Exchanger which functions similarly

to the radiator in your car. Coolant "antifree+e# is circulated through one side of theheat exchanger where it is cooled by raw water that asses through the other side of

the heat exchanger. !he engine coolant is then circulated back into the engine. !he

raw water is exelled out of the boat thru the exhaust. nother common tye of closed

cooling systems is known as a -eel Cooler. !his is done by eliminating the use of a

heat exchanger. nstead of uming raw water into the vessel/s heat exchanger where

it cools the coolant, the coolant is umed through ies or aluminum extrusions on

the outside of the hull where the surrounding water "lake or ocean water# cools the

coolant before it is umed back into the engine. !he use of keel coolers removes the

need for a heat exchanger, raw water um and the other comonents necessary for

 uming raw water into the heat exchanger to.

Fresh Water Cooling System using a Heat Exchanger

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Fresh Water Cooling Systems using a Keel Cooler

Closed cooling systems are more comlex than raw water cooling systems, but have

distinct advantages0

1. Minimal internal engine corrosion.

2. More effective at cooling the engine and allows you to run your engine at

higher temeratures, resulting in better engine erformance and fuel economy.

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How A Heat Exchanger Functions

Heat Exchanger transfers, or 3exchanges,3 heat from your

 boat engine/s coolant to raw water umed from the water outside of your boat. !he

raw water is umed through a bundle of small tubes in a chamber filled with the hot

engine coolant. !he tubes are cooled by the colder raw water the allowing the tubes to

absorb the heat of the engine coolant.

!o function correctly, a heat exchanger must be carefully matched to your boat/s

engine. )o2marine carries over 144 different models of heat exchangers from San

5uan Engineering , Seakam Engineering and Sen (ure

Expansion Tanks

Exansion tanks are an often overlooked but very imortant art of a closed cooling

system. s the engine coolant gets hot it exands, increasing in volume. !he

exansion tank is a small tank that simly rovides room for this increase in volume.

n some systems, the heat exchanger is a iggy back style. !his is when the exansion

tank is built on to of the Heat Exchanger. &n some Heat Exchanger systems, the

exansion tank is a searate tank remotely mounted. Most heat Exchangers have a

fitting built into the tank to install a 6ink node. !his sacrificial anode rotects the

Heat Exchanger form galvanic corrosion commonly known as Electrolysis. !he 6incshould, be checked once a month to insure rotection of the Heat Exchange and

 revent re'mature failures. nother imortant comonent to the Heat Exchanger is

the ca on exansion tank similar to the ca on your cars radiator. t is an imortant

comonent in, maintaining your cooling system/s ressure. t should, be checked

regularly for leakage and corrosion. !he boat engine arts secialists at )o2marine

recommend that you relace the ca on your exansion tank every two years.