1 ENGINE SYSTEMS 41
Cooling System Flow
The cooling system keeps the engine within
a designated temperature range. The major
components of the cooling system include the
following:
• Radiator and fan combination (chassis
components)
• Water pump assembly
• Thermostat assembly
• Oil system module assembly
• EGR cooler assembly
A belt-driven centrifugal water pump is set into
the front cover. The front cover has three related
passages. One passage channels coolant from the
water pump to the crankcase, the second returns
coolant to the water pump, and the third (a bypass)
channels coolant back to the water pump when the
thermostat is closed.
Incoming coolant flows from the bottom of the radiator
through a water inlet elbow to the front cover and water
pump. Coolant is pumped to the crankcase through a
passage in the front cover and crankcase.
Water jackets in the crankcase direct coolant from
front to rear, distributin g coolant evenly to the lower
sections of the cylinder sleeves. Coolant flow is
directed tangent to each cylinder sleeve, causing a
swirling mo tio n up to the cylinde r he ad. The swirlin g
action improves heat absorption.
Coolant flows from the cylinder sleeve areas in three
ways:
• Coolant flows into the oil system module
assembly through the right side of the cran kcase,
passes through the oil system module, and
returns through a tube to the front cover.
• Coolant is routed through hoses to and from the
air compressor on the left side of the crankcase.
• Coolant exits the crankcase at the upper end
of each cylinder sleeve bore and is distributed
evenly throug h metering holes in the c ylinder
head gasket. Coolant then flows through the
cylinder head (back to front) to the thermostat.
The EGR cooler receives coolant from the front cover.
Coolant fl ows from the front of the cooler and exits the
rear of the cooler into the rear of the cylinder head. A
deaeration port is on top of the EGR cooler.
Thermostat Operation
The thermostat has two outlets. One directs coolant
to the radiator when the engine is at operating
temperature. The other directs coolant to the water
pump until the engine reaches operating temperature.
The thermostat begins to open at 88 °C (190 °F) and
is fully open at 96 °C (205 °F).
Figure 34 Thermostat c
losed
1. C oolant flow to heater p
ort
2. C oolant in from engine
3. Bypass to water pump
When eng ine coolant is
belowthe88°C(190°F)
the thermostat is clo
sed, blocking flow to the radiato r.
Coolant is forced to
flow through a bypass port bac k
to the water pump.
EGES-270-1
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
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