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Transcript of 3387029coolingsysIntroToTroubleShootPrg1
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FOREWORD
Have you ever seriously thought about thecooling system in a diesel engine? Its purpose,
how it functions, and why?
In this program we've tried to cover these
questions well enough so that you can easily
understand them. We're sure that, when you
thoroughly understand this system, you will
become a highly-successful cooling-system
troubleshooter.
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1.
2. The purpose of this program is to familiarize you
with the theory and operation of the cooling
systems in Cummins Engines.
3. You can then apply this knowledge when you see
the second Cooling System Program, which will
deal with troubleshooting and failure analysis.
4. Some people feel that the cooling system consistsof a big radiator, and all you need to do is keep it
filled with water.
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5. Actually, water is a very important part of the
cooling system. So is the radiator or heat
exchanger. But these things make up only a small
portion of a complete system. This fact is easy to
believe if we understand the purpose of a cooling
system.
6. It performs four basic functions in an engine:absorption, circulation, control, and dissipation.
7. The coolant absorbs heat from areas around the
cylinder liners and cylinder heads. ( Remember
that heat flows from warm areas to cooler areas.)
8. The water pump circulates the coolant throughoutthe entire system.
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9. The thermostat, shutters, and the cooling fan
control engine coolant in order to keep it within.
the temperature range required for optimum
;engine operation.
10. A radiator or heat exchanger provides a way for
engine heat. to be removed, or dissipated, from the
engine coolant and transferred to the atmosphere,
or to an outside water source.
~11. Now we'll discuss each part of a modern cooling
system. Let's begin with the centrifugal water
pump. Although it's built in many Qifferent
configu rations,
12. it is basically a housing containing a shaft and
impeller assembly. As the impeller turns, it creates
a pressure differential across the pump.
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13. This pressure differential forces the coolant to
circulate through the system. The head of pressure
from the volume of coolant above the water pump
maintains a constant pressure at the water pump
inlet. This area must always be under a positive
pressure to aid in keeping air out of the system.
1~ Oil coolers are made in different.shapes .and sizes,
: ! but they all perform the same basic function.II
15. Coolant flows through the tubes In th is type of
cooler, while the oil flows around the outside ofthese tubes.
"
16. In the K series coolers, the coolant flows around
the outside of the element, wh ile the oil flows
through the element.
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17. So, during engine operation, the coolant helps
maintain a satisfactory lube oil temperature range.
18. As the coolant passes through the block and head
passages, it absorbs heat from the cylinder liners,
and the injector and valve areas.
19. Higher horsepower turbocharged engines use an
aftercooler to cool the air coming from the turbo.
20. During normal ehgine operation, coolant flows
through the core tubes. At the same time, intake
air is passing from the turbo around theaftercooler core tubes. After being compressed,
this air is usually much hotter than engine coolant.
So the coolant absorbs a portion of the heat from
the intake air, and carries it through the the
.radiator or heat exchanger ..
~
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21. The thermostat is located in the main coolant
stream, near the upper, front part of the engine,
just before the radiator or heat exchanger.
22. The heat sensor protrudes toward the engine side
of the thermostat housing.
23. It is basically a sturdy, pfessure-tight capsule
containing a thermal expansion material, usually a
composite of wax and copper powder. As the
engine coolant heats the sensor, the wax melts and
expands, gradually moving a stainless-steel shaft a
predetermined distance. This movement causes the
thermostat body to open, allowing coolant to flow
to the radiator .
24. Until 1975, new engines were equipped with two
basic types of by-pass thermostat -vented and
non-vented, Now the vented thermostat is no
longer current for service. It contains a "V" notch
which allows a small ~mountof coolant and air to
bypass the valve during fill and during engine
operation. The small amount of by-passed coolant
may cause a lightly-loaded engine to run extremely
cold. A shutterless system tends to intensify t.hi~problem of cold operation. .
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..25. The ventless thermostat is usr..-j In a positive-flow
deaerating system. This system purges air from the
eng,ine during fill and du'ringoperation via a vent
line running from the engine side of the
thermostat housing to the upper part of the
radiator, heat. exchanger or expansion tank. The
ventless thermostat prevents any flow through the
radiator core when the thermostat is closed.
26. The thermostat seal keeps the coolant from
passing on to the radiator when the thermostat isclosed.
27. Radiators are bu ilt in two basic styles: vertical and
cross-flow. There is no difference between their
basic functions. The cross-flow type was designed
for low-profile installations.
28. In the vertical type, the top tank consists of a
sealed baffle plate, a fill line connecting the top
tank to the water pump, a coolant inletconnection, a vent line connecting the radiator
core to the top tank cavity, a vent line inlet from
the engine, and a fill neck with an overflow line.
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29. The area between the top of the top tank and tht:baffle plate is the reserve volume. 1"his space servesas a reservoir to store make-up coolant to be used
when water is lost from evaporation and minor
leaks.
30. It also provides space for thermal expansion.
Through a 40° to 200°F. temperature range,lwater
expands at the r-ate of approximately 1/3 pint for
each gallon in the system.! When 50% anti-freeze is
added, this expansion' increases slightly. If
expansion space is not provided, this amount of
coolant will be lost through the overflow line.
31. The cooling system should be filled at the rate ofapproximately five gallons per minute. During this
time, the co'Qlant flows through the ~i" line, into
the system.
32. At this time, air is escaping through the vent lineand vent tube to the reserve volume in the radiator
top tank.
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33. The bottom of the fill neck dictates the coolant
level. When the coolant reaches this point, a small
amount of air pressure escapes through a bleed
hole in the filler neck. But this air escapes so
slowly that it barely allows coolant to be added,
even at a very slow rate.
34. During initial engine operation, the water pump
forces pressurized coolant through engine passages.Since the engine is cold, the thermostat is closed,
and the coolant is routed through the bypass tube,
back into the water pump and engine, and anyaccessories attached to the engine side of the
thermostat.
35. When the engine coolant reaches normal operating
temperatures, the thermostat is open. Most of thecoolant is then routed through the radiator inlet
line to the radiator core, below the top-tank baffle
plate.
36. At this time coolant is expanding, rising past thebottom of the fill neck. The bleed hole allows the
gradual build-up of air pressure to escape directlyto the pressu e cap area.
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37. Without this bleed hole, air pressure would force
the coolant {and any air in the fill neck) out of the
system as it expanded.
38. An auxiliary tank is sometimes used on
installations that do not have an integral
deaerating system, or on installations with "fill"
problems, due to the radiator being lower than the
engine, or space limitations. This tank performs
the same functions as the "reserve volume" area in
a positive-flow system top tank.
39. The standard cross-flow radiator, as we mentioned
earlier, performs the same functions as the vertical
type, in a standard, positive-flow system. As the
system is being filled, coolant flows through the
fill line. In this way, both the radiator and engineare filled from the bottom up. This action vents air
from the engine and radiator core through the
venturi and ',U" tube, and the core vent line, to
the "reserve volume" area.
40. During normal engine operation, with the
thermostat open, coolant enters this radiator atthe upper left, and exits at the lower right. Any
entrapped air continues to be v~ted to the reservevolume area.
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41. In some installations, it is necessary, and usually
convenient, to use a heat exchanger in place of a
radiator. This is especially true for marine
applications, where it is not desirable to blow a
great deal of heat into the cabin area from a
cooling fan. Sea water is used to absorb and
dissipate engine coolant heat.
42. The heat exchanger works exactly like an oil
cooler. A sea-water pump circulates sea water
through the heat exchanger tubes, then back to
the sea.
43. At the same time, engine coolant is flowing from
the engine, around the outside of these tubes, then
back to the engin~. In th is way, outside water
carries away the heat from the engine coolant.
44. Engine coolant is vented to the expansion space in
the heat exchanger housing to allow deaeration
during fill and engine operation.
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45. In keel-cooling applications, the heat exchangerfunction takes place as the engine water Is cooled
by the keel cooler. With the heat exchanger core
removed, the housing now becomes all expansionspace. In either system; an auxiliary tank may be
added to the system to provide reserve coolant and
reserve expansion capacity. Notice the 'coolant
flow in the gear oil cooler (left bank). Coolant
flows through the element tubes, while the gear oil
flows around the outside of the tubes.
46. Many institutio,nal installations use heat
exchangers. Fresh water is piped to the heatexchanger from the city water supply or from
private wells.
.47. The main purpo~ of a radiator pressure cap is to
increase the pressure level of the total system. A
positive pressure (greater than atmospheric
pressure) not only prevents the entry of more air
in the system, but it reduces the volume of air that
is already in the system, and it raises the boiling
point of the water .
48. A pressure cap has two valves -a pressure valve
.and a vacuum valve. As the coolant expands during
engine operation, the pressure valve regulates
maximum pressure by opening and allowing the
escape of excessive pressu re.
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.49. When the engine is shut down and begins to cool,
the pressure valve is closed. The vacuum valve is a
"relief valve" which prevents a vacuum in the
cooling system. It opens at this time and allows
outside air to re-enter the expansion space,
thereby equalizing the pressure between the
system and the atmo~phere. In this way, the valves
assure close regulation of system pressure during
the heating and cooling periods.
\
.50. The pressure cap raises the boiling point of the
coolant. At an atmospheric pressure of 29.92 in.
Hg., water will boil when its temperature reaches
212°F. (100C.).
.51. However, when air pressure in the top tank
exceeds the vapor pressure of the coolant, the
water cannot boil. And it won't boil until the
vapor pressure exceeds the regulating pressure of
the pressure cap valve, and escapes to the
atmosphere.
~
.52. Tests have shown that depending on many
variables, e=3ch additional psi of air pressure willraise the boiling point of the coolant by
approximately 3°F. This is especially important at
altitudes where the boiling point is much lower,
due to low atmospheric pressure.
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.53. So what would happen if the pressure valve was
blocked in the closed position? Right! The coolant
pressure would eventually rupture the weakest
area in the system -usually in the radiator core or
a water hose.
.54. And what wou Id happen if the vacuum valve sticksopen? Right again! The system would notpressurize, and boiling would occur at much lower
tern peratu res.
55. If you suspect that the cap is defective, check it
with a pressure pump. Set the pump gauge at the
psi shown on the cap. If the cap does not release
the pressure near this setting, it should be
replaced.
If you suspect that the vacuum valve is defective,
shake the cap. If the vacuum valve is proper1y
seated, it will not rattle.
56. Cooling system hoses must be relatively flexible,
yet rigid enough so they will not collapse. They
should have smooth inner walls. Hoses with
coil-wire reinforcement, or the highly-flexible
"accordion" hoses, will create water turbulence.
This design reduces the effective diameter of the
hose, and causes a significant pressure drop in the
system.
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57. Another part closely associated with the radiator is
the radiator shutter assembly. Shutters are used as
a supplement to the engine thermostat to assist in
maintaining minimum coolant temperatures during
engine operation. They accomplish this by
regulating the air flow across the radiator core and
through the engine compartment.
58. The shutterstat control is a heat-sensitive device
which uses the force of air pressure, vacuum,
engine lube oil, or electric power to open and close
the shutters. Manual controls are also available.
The shutterstat control is usually installed in the
coolant flow in the thermostat housing.
~
59. The cooling fan plays an important role in the
cooling system. The main function of a fan is to
pull or push air through the radiator core. This air
carries away the coolant heat as the coolant passes
through the core tubes and fins.
.60. Fans come in a wide variety of blade shapes, pitch,
hub types, diameters, and materials to fit almost
any type of installation.
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61. Equally important are the drives. Very popular
nowadays, because of the horsepower savings and
the no ise reduction, are the
temperature-controlled, or "thermatiG "fan drives.
This "ON-OF F" type of drive is air-operated..
When the air temperature drops to a
pre-determined level, air pressure forces a built-in
clutch to disengage from the fan hub.
62. Variable-speed viscous fan drives are
air-temperature controlled by means of a leaf-type
bi-met~1 located on the front of the fan. This
device senses air ter1'1perature changes in the air
that has passed through the radiator core.
63. The bi-metal moves an internal valve which
regulates the flow of a viscous fluid from a
reservoir. The amount of fluid in the drive area
controls the fan speed.
64. Thermatic fan and shutterstat controls must be setaccording to the specifications in the appropriate
Operation and Maintenance Manuai.
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-65. Fan shrouds are used on many installations to
improve cooling efficiency, provide a uniform
distribution of air over the core, and to restrict the
recirculation of air around the fan blades.
.66. Recirculation baffles around the radiator help
prevent the recirculation of hot air through the
radiator core. If these baffles are damaged or
removed, engine coolant temperatures may rise
much higher than normal.
-67. The inside of the radiator core, as well as the restof the cooling system, must be free from
obstructions.
.68. If rust. and scale have collected in the system, it
must be chemically cleaned, then flushed with agood neutralizer and clean water .
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69. The system should also be thoroughly cleaned and
flushed when anti-freeze is added or removed, or
before installing a water filter on anew engin~.
Nc 2 t
.70. The DCA Water Filter is a definite "must" in a
cooling system. This filter performs four functionsin an engine. .
~ 71. One, it provides a positive method of filtering out
dirt, rust particles, and ot:her foreign material from
the cooling system.
72. Two, it controls the acidity level in the coolant byreleasing special buffering agents in the system.
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.73. Three, it slows down the formation of rust by
adding a corrosion-inhibiting chemical to the
coolant. This chemical prevents corrosion of
cylinder Ijners, solder, aluminum, copper and
brass.
,74. And four, rt slows down the rate of scale build-up
by softening the water .
75. A test kit Is available for checking the coolant to
make sure that filter servicing or concentration of
DCA inhibitor is adequate (but not excessive) to
control corrosion for any specific operatingcondition.
76. For information concerning complete maintenanceprocedures, refer to CST program No.3387001and the appropriate Operation and Maintenance
Manual.
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77. Drive belts playa most important role in a cooling
system. Although K engines have gear-drjven water
pumps, all other current production engines use
drive belts for water pumps and radiator fans.
78. Cummins I engines use either V-belts or Poly-V
belts. V-belts contain either rayon or polyester
cord. Polyester-cord belts are tougher and more
durable than comparably.;sized rayon belts.
79. Poly-V belts are used mainly on K engines. The
term "Poly' as used here, simply means that the
belt contains several "V" channels.
80. Cog-type belts are used with small pulleys. The
spaces between the cogs allow the belt to bend in a
smaller radius with less strain.
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81. When replacing belts, always shorten the distance
between pulley centers. Rolling a belt over a
pulley, or using a screwdriver, will ~amage the belt
and cause an early failure.
82. Always replace belts as a complete new set, of the
same manufacture and the sar'ne length. Thes.e
belts will assume equal loads, and will stretch at
the same rate, giving maximum service.
~3. Let's assume that a new belt is installed with a set
of old belts. The new belt is the same length as the
old ones, but the part number and manufacturer
.are different. Would this arrangement work OK?
Definitely not! The new belt will stretch, while the
old belts remain the same. This throws the full
load on the old belts.
84. Or, let's say that a new belt is installed with an old
set of the same part number and manufacturer.
Now what happens? Still bad news The old
belts are already stretched. So, for awhile, the new
belt carries the full load, and it will probably fail
in a short period of time.
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85. Misalignment of pulley grooves must not exceed
1/16 inch per foot of distance between pulley
centers. Angular misalignment must not exceed
one-third of one degree.
86. Belts must not bottom on pulley groove~, norshould they protrude more than 3/32 inch abovethe top edges of the grooves. Riding depth mustnot vary over 1/16 inch on matched belt sets.
87. Always keep the belts tightened to the proper
tension. Follow the instructions and specifications
in the appropriate Operation and Maintenance
Manual.
88. We've discussed most of the cooling system parts
and their functions. Now we'll take a look at the
coolant flow through some of our engines.
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89. In the earlier 855 Cu. In. engine, coolant flows
from the water pump through the engine. When
the engine is cold, the coolant is bypassed from
the engine side of the thermostat housing to the
oil cooler. It is recirculated through the engine and
any accessories attached to the engine side of the
thermostat. A portion of the coolant flow
bypasses through the water filter during engine
operation. (Remember, a vented thermostat would
allow a small amount of coolant to flow through
the radiator at this time.)
90. When the engine reaches normal operating
temperatures, the thermostat opens. Coolant thenflows through the radiator, oil cooler, and back tothe water pump.
91. On NT A engines, coolant flows from the rear
block water header, through the aftercooler core,then to the thermostat housing. Coolant also flows
through the air compressor.
92. In the FFC engine, coolant flows from the water
pump to the water header plate. At this point,
approximately 1/3 of ttle coolant is divertedthrough the oil cooler and water transfer tube tothe thermostat housing.
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93. The remaining coolant circulates through theengine, and back to the thermostat housing. Whenthe thermostat is closed, coolant flows through theby-pass tube, back to the water pump. (Coolant is
continually by-passed through the water filter
during engine operation.)
94. When the engine reaches normal operattng
temperatures, the thermostat opens. Coolant then
flows through the radiator, directly back to the
water pJmp. Coolant flow in the engine
accessories, such as the water filter, cab' heater, or
air compressor, is similar to that in the NT A
engine.
95. In the KT -6 engine, coolant flows from the water
pump through the oil cooler, then through the
cylinder block, cylinder heads, water manifolding,
and to the thermostat housings. .From here the
coolant flows through the by-pass tube back to thewater pump. Coolant is continuously by-passed
from the pump, through the water filter, and back
to the pump.
96. When the engine reaches normal operating
temperatures, the thermostat opens. Coolant' isthen routed through the radiator, then back to the
water pump,
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97. I n the V -1710 engine, coolant flows from the
water pump, through the oil cooler, rear block Vee
connection, and block Vee water header. From
this point, it flows to the aftercoolers, block liner
cavities, cylinder heads and exhaust manifolds (if
water-cooled). These flow circuits lead to the
thermostat housings. Then, depending on engine
temperatures, .coolant bypasses back to the water
pump or flows to the radiator/heat exchanger.
98. In the V-504 marine engine, coolant flows from
the water pump, around the cylinder liners, to the
cylinder heads and exhaust manifolds, then to the
thermostat housing. At this point, coolant flows
back to the water pump or through the heat
exchanger, depending on engine operating
temperature. Coolant flows continuously, in a
bypass circuit, from the cylinder block to the
engine and gear oil coolers, and back to the block.
99. In the V-903 engine, coolant flows from the waterpump to the oil cooler, right-bank water header
plate, right-bank cylinder Hners, cylinder head, andright-bank thermostat housing. At the same time,
coolant flows from the water pump through thewater crossover to the left-bank water header
plate, cylinder liner.s, head and thermostat
housing. Depending on engine .operatingtemperatures, coolant flows directly back to thewater pump or through the radiator, then back tothe .pump.
100. We've discussed most of the basics involved in
Cummins cooling systems, including coolant,0
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101. cooling system parts,
102. and coolant flow through several engines.
103. As we mentioned earlier, the main purpose of this
program is to prepare you for troubleshooting this
system. Remember, "effective, successfuJ
troubleshooting requires a thorough knowledge ofthe engine systems, parts and functions".
104.
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