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 TM 5-685/NAVFAC MO-912
become so hot that it loses its lubricating properties
(8) It is necessary to control temperatures at
or breaks down.
various points of the engine and throughout the
(f) Coolant leaving the oil cooler flows to the
cooling systems. This may be done by bypassing
cylinder water jackets, inlet ports and valves, injec-
some portion of a coolant stream or by changing the
tors, exhaust ports and valves, intercooler or super-
flow rate.
charger, turboblower, exhaust manifold jacket, and
(9) Overcooling can cause problems. A warm
finally to the heat exchanger where it is recircu-
engine is easier to start and can quickly be brought
lated to the engine.
up to speed and loaded. Warm oil provides better
(5) Non-contact heat exchangers are used to
initial oil circulation and lubrication which is vital
add or remove heat from one medium to another
in cold weather. Heavy fuel oils must be at a tem-
without intermixing. A radiator or fin-fan cooler
perature related to the viscosity required by the fuel
uses an airflow to remove and dissipate the heat. In
system and injectors. The carburetor and inlet
a heat exchanger, one medium flows through tubes
manifold of an SI engine must be warm enough to
and the second medium flows around the tubes.
prevent "icing" and to vaporize the fuel/air mixture.
Generally, the medium having a higher tendency to
Exhaust gas temperature must be kept above the
foul the exchanger surfaces is inside the tubes to
dew point to prevent condensation and corrosion.
allow easier cleaning. The tubes may form part of a
An engine running cold will not achieve rated effi-
sealed system. The tube bundle may be in an open
ciency. Freezing of the coolant can cause breakage
tank or in a shell. The shell, enclosing the second
or interfere with required flow and circulation.
medium, may be part of another sealed system.
(10) Chemical control of the various cooling cir-
(6) Cooling towers and evaporative coolers are
cuits is important. Strainers and filters remove sus-
both used to dissipate waste heat to the atmo-
pended solids. Additives prevent corrosion, mineral
sphere. They may be used where ambient air is
scale buildup, organic growth and organic fouling.
sufficiently cool and dry (low relative humidity) to
Periodic sampling and analysis will indicate actual
absorb water vapor. As water is sprayed or divided
concentrations of undesired materials dissolved in
into many small streams, some will evaporate to the
the coolants. Comparison of test results will provide
passing air. The heat required to evaporate the wa-
guidance for altering the treatment program. Some
ter is approximately 1050 Btu/lb and is extracted
untreated freshwater and brackish or seawater pro-
from the unevaporated water. Additionally, the air
mote growth of barnacles, etc., that prevent proper
which is now moist may be warmed by the water (if
flow and pressures. Visual inspection is recom-
the water was originally warmer than the air), thus
mended when increasing pressure drops indicate
removing more heat from the water. In a cooling
fouling. Physical and/or chemical cleaning may be
tower, the fluid to be cooled is exposed to the air.
periodically required. Safety precautions must be
Approximately eighty percent (80%) of the heat re-
followed when using most cleaning compounds.
moved is due to evaporation. The water leaving the
3-6. Lubrication system.
tower or cooler is usually five degrees Fahrenheit
(5F) higher than the entering air. Towers may use
The bearings and moving parts of all diesel engines
atmospheric draft or fans to move the air. Makeup
are lubricated by a full-pressure system, see figure
water is required to replace that lost by evaporation
3-6. Lubricating oil requirements and specifications
or entrained spray. Water treatment and blowdown
are covered in appendix C.
a. System elements. Smaller engines are usually
are necessary because salts are concentrated by the
evaporation. Dust, etc., in the air will contaminate
self contained. The smaller engine system will have
the exposed water. In an evaporative cooler, the
many of the system elements used in the larger
engines, as follows:
coolant passes through tubes. The tube bundle lies
inside a cooling tower. The cooling tower spray and
(1) Lube oil h aving proper properties for the
air movement cool the tubes but do not mix with the
specific engine design.
coolant.
(2) Lube oil ank or sump to hold the volume of
t
(7) Flow rates of fluid, fan speed, flow bypass,
oil required.
etc. are controlled to maintain proper conditions. A
(3) Oil feed pump(s) driven from the engine to
properly monitored, real-time, automatic control
circulate clean cool pressurized oil (5 to 75 psi).
system is preferred over a manually-operated sys-
(4) Oil feed piping, valves and controls to de-
tem, especially where some parts of the engine aux-
liver oil to various lube points of the engine.
iliaries are remote or not in direct observation of
(5) Engine internal oil passageways in the
crankshaft-piston assembly and in block and head.
operating personnel. Automatic data logging is of
real value for determining trends and for trouble-
(6) Hot oil sump to collect oil draining from all
shooting.
the lubricated engine components.
3-12
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