TM 5-685/NAVFAC MO-912
Table 3-4. Typical cooling system components.
also decreases heat transfer. It should have good
heat capacity and contain an antifreeze, anti-
corrosion compound, and cleaning agent to keep
The liquid, usually treated water, used to re-
coolant passages in good condition. The coolant
move excess heat from the engine. May be pri-
should neither corrode nor attack any metals or
mary, secondary. etc.
organic materials of the coolant system. It should
Spaces surrounding block, cylinders, and heads,
not be hazardous.
through which primary coolant is circulated
(4) In rare cases, the engine may be cooled us-
under pressure to cool the engine components.
ing clean water in a once-through system. Cool wa-
Water or primary (secondary, other) pump to
ter is pumped through the coolant passages, and the
circulate coolant (water) through engine pas-
hot water leaving the engine is discarded. This has
sages to heat exchangers.
many disadvantages and will not be further dis-
Regulates coolant flow to maintain engine tem-
perature between specified limits.
(a) Smaller engines may have a single cool-
Provides air movement to cool air-cooled en-
ant circuit (loop) through which coolant, leaving the
gine or the radiator of a liquid-cooled engine to
engine, passes and is returned to the engine.
cool the coolant for recirculation.
(b) Larger engines may require the use of
Blades used to vary air flow across a radiator
additional loops. In these, the engine coolant is in a
to regulate rate of heat removal from coolant.
primary loop. It is cooled by the medium circulating
Would be closed when coolant is below normal
temperature and open when coolant is warm.
in a secondary loop and the secondary coolant may
May be thermostatically controlled.
be cooled by another medium in a tertiary loop. No
cooling medium mixes with another medium in
A device to exchange heat from one medium to
another. Usually a shell and tube-type ex-
these "non-contact" systems.
(c) An example of a three-loop system is
A structure in which hot coolant is sprayed or
treated engine coolant in the primary loop passing
falls through air currents. As coolant evaporates
through a heat exchanger cooled by freshwater in a
heat is given up by the remaining liquid cool-
secondary loop. The "hot" freshwater may be used
for building heating or may be passed through an-
A device to remove heat from medium by
other heat exchanger cooled by brackish or saltwa-
evaporation of that medium in air (open cir-
ter in the tertiary circuit on a once-through basis.
cuit). May also be by non-contact heat ex-
changer from one medium to an evaporating
The purpose of this arrangement is to keep the
second. Applicable where ambient temperature
seawater at low temperatures so that salts do not
and relative humidity are below certain values.
form scale. Leakage of seawater into the freshwater
Coolant fluid, usually filtered water with addi-
circuit is prevented by having the freshwater at
tives to prevent freezing and to inhibit scale
higher pressure than the seawater. The freshwater
formation and corrosion. Required for primary
circuit may operate at higher temperature and re-
coolant circuit. May not be required for sec-
cover significant usable heat otherwise wasted.
ondary or other circuits.
Contamination of engine coolant is prevented by
Describes the components of a second system
being at a higher pressure than the freshwater. The
used to extract heat from the primary heat ex-
additives used in the engine coolant are a cost. Very
changer. Used where waste heat may be used
for building heating, etc.
little coolant is lost when the coolant circuit is
sealed. Heat capacity and temperature may be el-
Describes components of a possible third sys-
evated by using a sealed, pressurized coolant loop.
tern to extract heat from a secondary system.
Coolant must be periodically tested to make sure
Coolant does not come in contact with air or
correct amounts of active additives are present.
(d) At the e ngine the coolant cools the lubri-
cating oil, then the lower temperature areas, and
consumption and mechanical energy output. The
finally the hotter sections.
coolant must not contain any suspended solids that
(e) In the crankcase the oil cools the crank-
could settle and impede heat transfer or coolant
shaft assembly. Sprayed or splashed oil cools the
flow. The coolant should be free of entrained or
underside of the piston. Oil circulated to the cam-
dissolved air or other gases which could cause cor-
shaft, rocker arms, and valve guides picks up heat
rosion and decrease heat transfer. The coolant
and drains into the sump. The oil pump forces the
should not contain dissolved salts' that could pre-
hot lube oil through the oil filter and through the oil
cipitate or form an insulating scale coating which
cooler to the pressure-oiled points. The oil must not