COOLING SYSTEM 
CONTENTS page 
DIAGNOSIS
 ... 4 
ENGINE
 ACCESSORY
 DRIVE BELTS
 40 
ENGINE
 BLOCK HEATERS
 48 
GENERAL
 INFORMATION 
 Throughout this group, references are made to partic
ular vehicle models by alphabetical designation or by 
the particular vehicle nameplate. A chart showing a 
breakdown of alphabetical designations is included in 
the Introduction section at the beginning of this man
 ual. 
 5.9L gas powered engines will be' referred to as ei
ther: LDC (Light Duty Cycle) or HDC (Heavy Duty 
 Cycle). 
COOLING
 SYSTEM 
 The cooling system regulates engine operating tem
perature. It allows the engine to reach normal oper-
 page 
SERVICE
 PROCEDURES
 15 
SPECIFICATIONS
 ; 49 
ating temperature as quickly as possible. It also 
maintains normal operating temperature and pre
vents overheating. 
The cooling system also provides a means of heat
ing the passenger compartment and cooling the auto
matic transmission fluid (if equipped). The cooling  system is pressurized and uses a centrifugal water 
pump to circulate coolant throughout the system. 
An optional factory installed maximum duty cool
ing package is available on most models. This pack age will provide additional cooling capacity for 
vehicles used under extreme conditions such as 
trailer towing in high ambient temperatures. 
 NOTE: HEATER 
COOLANT FLOW 
CIRCUIT
 IS
 ALWAYS 
OPEN
 EXCEPT 
WHEN
 IN MAX. A/C 
 OR
 OFF
 MODES 
HEATER 
INTAKE MANIFOLD 
COOLANT FLOW "METERED"  FROM REAR
 TO 
FRONT
 AND
 BELOW  EXHAUST
 HEAT 
CROSSOVER 
 SHUT
 OFF
 VALVE 
A/C
 ONLY  COOLANT FLOW
 -
 PUMP
 TO 
CYLINDER BLOCK,
 UP
 THROUGH  CYLINDER HEADS
 TO
 INTAKE MANIFOLD WATER
 BOX TO 
 RADIATOR-TO PUMP 
•BYPASS 
 THERMOSTAT CLOSED-HIGH FLOW 
THERMOSTAT OPEN
 - LOW
 FLOW 
 J9207-18 
Fig.
 1
 Cooling
 System
 Routing—3.9U5.2L Engine—Typical   
• 
AUTOMATIC
 TRANSMISSION—32RH/36RH/37RH/42RH/46RH
 21-103 
TRANSMISSION DIAGNOSIS 
Condition 
 Possible
 Couso 
 Correction 
OVERHEAT
 DURING 
COMMERCIAL
 OPERATION 
OR
 WHILE
 TRAILER
 TOWING 
 (FLUID
 DARK
 AND
 BURNED 
WITH
 SOME
 SLUDGE 
 FORMATION) 
 1.
 Vehicle not properly equipped for
 trailer
 towing or 
commercial use 
2. Vehicle not equipped
 with
 auxiliary fluid cooler 
3.
 Extensive idling
 time
 or operation in heavy
 traffic
 in  hot weather 
4. Tow vehicle overloaded (exceeding vehicle tow  capacity) 
5. Air flow to auxiliary cooler blocked by snow plow, 
 front
 mounted spare
 tire,
 bug screen, or similar
 item 
 1.
 Be sure vehicle is equipped
 with
 recommended 
optional components
 (i.e.,
 HD
 springs, 
transmission,
 axle, larger CID engine, auxiliary  cooler, correct axle ratio, etc.). If vehicle is not so 
equipped, it should not be used for severe 
service operation 
2. Drain fluid, change
 filter,
 and install auxiliary  cooler 
3.
 Cut down on idling time; shift into
 neutral
 every 
 so
 often and run engine at 1000 rpm to help 
circulate fluid through cooler 
4. Be sure vehicle is properly equipped to handle 
 load;
 do not tow
 Class
 Ill-type loads
 with
 a 
vehicle
 that
 is only
 rated
 for
 Class
 1
 or II  operation 
5.
 Remove or reposition
 item
 causing
 air flow 
 blockage 
OVERHEAT
 DURING
 NORMAL 
 OPERATION
 (FLUID 
DISCOLORED,
 SMELLS 
BURNED) 
 1.
 Low
 fluid
 level 
2. Fluid cooler, lines blocked, or cooler cracked (oil in  engine coolant) 
3.
 Switch valve sticking 
4. Clutch pack clearance incorrect (too tight) 
5.
 Bands
 too tight  1. Add
 fluid
 and check for leaks 
2. Flush cooler and lines and replace radiator if 
 transmission
 fluid has
 entered
 coolant 
3.
 Remove,
 disassemble,
 clean valve body 
4. Check and correct as required 
5. Adjust bands 
J9121-450