Base Engine Operation
03
120
9
RG,RG34710,1521 –19–09SEP02–2/3
A—Coolant Pump F—Directed Top Liner Cooling I—Water-to-Air Aftercooler L—High Temperature Coolant
B—Coolant Heater Passages Supply M—To Radiator Top Tank
C—Coolant Manifold G—Directed Top Liner Cooling J—Water-to-Air Aftercooler N—From Radiator
D—Thermostats Return Line Return O—Coolant Passage
E—Thermostat Housing H—Coolant Bypass Tube K—Low Temperature Coolant P—Unit Injector Sleeve
The pressurized cooling system consists of a radiator
(not shown), coolant pump (A), coolant heater (B),
coolant manifold (C), coolant passages in block and
the cylinder head, thermostats (D), and thermostat
housing (E).
The coolant pump draws coolant from the radiator
through the lower radiator hose. Flow then goes past a
coolant heater and into the oil cooler housing. Coolant
flows around the oil cooler and then flows into one of
two circuits.
The main circuit flows coolant from the oil cooler into
the coolant manifold. The coolant manifold extends the
length of the right side of the block. From the coolant
manifold, coolant flows into each liner cavity. From the
liners, coolant flows up into the cylinder head.
The coolant flow through the block and cylinder head
is optimized to provide ample flow around each liner
and to provide more flow to the rear of the cylinder
head than into the front. To achieve this, the coolant
passages from the block to the cylinder head vary in
size and in number.
The holes on the right side of the block are smaller
than the holes on the left side. Therefore, as coolant
flows out of the coolant manifold on the right side of
the block, it is forced to flow around the liners to
escape through larger holes on the left of the block.
This assures that each liner is surrounded by coolant
flow.
In addition, there are more holes and larger holes at
the rear of the cylinder head than at the front.
Cylinders 1 and 2 have one 6.3 mm (0.25 in.) and one
9 mm (0.35 in.) hole. Cylinders 3 and 4 have two 6.3
mm (0.25 in.) and two 10 mm (0.39 in.) holes.
Cylinders 5 and 6 have two 10 mm (0.39 in.) and two
16 mm (0.63 in.) holes.
The larger and higher number of coolant flow holes
around cylinders 5 and 6 force more coolant to flow to
the back of the cylinder head than to the front.
Once coolant is in the cylinder head, all flow is towards
the front. Coolant from cylinder 6 flows forward and
accumulates with flow from other cylinders. All coolant
flow then exits out the head at number 1 cylinder to
the thermostat housing.
The second circuit is called the “directed top liner
cooling” system. Two drilled passages (F) at the top of
the oil cooler cavity in the cylinder block route coolant
to cylinders 3 and 4 liners for top liner cooling.
Coolant will flow around the top of cylinder 3 liner, then
flow forward to cylinder 2 liner and then to cylinder 1
liner. Coolant will leave cylinder 1 through a drill
passage to the thermostat housing. Coolant entering
number 4 cylinder will flow rearward to number 5 and
then to number 6. Coolant leaves number 6 cylinder
through a drilled passage and flows though an external
steel line (G) to the thermostat housing.
When the engine is cold, the thermostats will be
closed. Coolant will flow through the bypass tube (H),
into the inlet of the coolant pump.
When the engines warms to operating temperature,
the thermostats will open and coolant will flow past the
open thermostats to the radiator (M).
The thermostat housing contains two thermostats. The
bottom thermostat has a blocking poppet. When the
engine gets to operating temperature, this thermostat
will open and allow flow to the radiator. The blocking
will close off the bypass path to the coolant pump inlet.
CTM100 (06APR04)
03-120-9
P
OWER
T
ECH
10.5 L & 12.5 L Diesel Engines
040604
PN=341
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