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COOLING SYSTEM
7 - 1
COOLING SYSTEM
CONTENTS
page
page
DIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
ENGINE ACCESSORY DRIVE BELTS . . . . . . . . 31
ENGINE BLOCK HEATER . . . . . . . . . . . . . . . . . 37
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . 1
SERVICE PROCEDURES . . . . . . . . . . . . . . . . . . . 9
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . 38
GENERAL INFORMATION
Throughout this group, references are made to par-
ticular vehicle models by alphabetical designation
(XJ or YJ) or by the particular vehicle nameplate. A
chart showing a breakdown of alphabetical designa-
tions is included in the Introduction section at the
beginning of this manual.
of cooling fins. XJ models equipped with a 4.0L 6 cyl-
inder engine and heavy duty cooling and/or air con-
ditioning also have an auxiliary electric cooling fan.
COOLING SYSTEM COMPONENTS
The cooling system consists of:
•
A radiator
•
Cooling fan (mechanical and/or electrical)
•
Thermal viscous fan drive
•
Fan shroud
•
Radiator pressure cap
•
Thermostat
•
Coolant reserve/overflow system
•
Transmission oil cooler (if equipped with an auto-
matic transmission)
•
Coolant
•
Water pump
•
Hoses and hose clamps
COOLING SYSTEM
The cooling system regulates engine operating tem-
perature. It allows the engine to reach normal oper-
ating temperature as quickly as possible, maintains
normal operating temperature and prevents over-
heating.
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 heavy duty cooling
package is available on most models. The package
consists of a radiator that has an increased number
SYSTEM COOLANT ROUTING
For cooling system flow routings, refer to Figs. 1, 2,
3 or 4.
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COOLING SYSTEM
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Fig. 1 Coolant Flow—XJ Models with 2.5L Engine—Typical
Fig. 2 Coolant Flow—YJ Models with 2.5L Engine—Typical
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COOLING SYSTEM
7 - 3
Fig. 3 Coolant Flow—XJ Models with 4.0L
Engine—Typical
Fig. 4 Coolant Flow—YJ Models with 4.0L
Engine—Typical
7 - 4
COOLING SYSTEM
DIAGNOSIS
INDEX
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page
Preliminary Checks
........................ 5
DRB Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
On-Board Diagnostics (OBD) . . . . . . . . . . . . . . . . . 4
ON-BOARD DIAGNOSTICS (OBD)
FOR COOLING SYSTEM COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor the certain following cooling
system components:
•
If the engine has remained cool for too long a pe-
riod, such as with a stuck open thermostat, a Diag-
nostic Trouble Code (DTC) number 17 can be
observed at the Check Engine Lamp.
•
If an open or shorted condition has developed in
the relay circuit controlling the electric radiator fan,
a Diagnostic Trouble Code (DTC) number 35 can be
observed at the Check Engine Lamp.
If the problem is sensed in a monitored circuit of-
ten enough to indicate an actual problem, a DTC is
stored. The DTC will be stored in the PCM memory
for eventual display to the service technician. If the
problem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be en-
tered into PCM memory. The criteria may be a spe-
cific range of engine rpm, engine temperature and/or
input voltage to the PCM.
A DTC indicates that the PCM has recognized an
abnormal signal in a circuit or the system. A DTC
may indicate the result of a failure, but never iden-
tify the failed component directly.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. Refer to On-Board Diagnostics
(OBD) in Group 14, Fuel Systems for additional in-
formation.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the Malfunction
Indicator Lamp. This lamp was formerly referred to
as the Check Engine Lamp. The lamp is located on
the instrument panel.
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
connects to the data link connector in the engine
compartment (Figs. 5 or 6). For operation of the
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.
Fig. 5 Data Link Connector—YJ Models—Typical
Fig. 6 Data Link Connector—XJ Models—Typical
EXAMPLES:
•
If the lamp flashes 1 time, pauses and flashes 7
more times, a flashing Diagnostic Trouble Code
(DTC) number 17 is indicated.
•
If the lamp flashes 3 times, pauses and flashes 5
more times, a flashing Diagnostic Trouble Code
(DTC) number 35 is indicated.
After any stored DTC information has been ob-
served, the display will end with a flashing DTC
number 55. This will indicate the end of all stored
information.
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ERASING TROUBLE CODES
After the problem has been repaired, the DRB scan
tool must be used to erase a DTC. Refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual for operation of the DRB scan tool.
COOLING SYSTEM
7 - 5
DRB SCAN TOOL
For operation of the DRB scan tool, refer to the ap-
propriate Powertrain Diagnostic Procedures service
manual.
PRELIMINARY CHECKS
ENGINE COOLING SYSTEM OVERHEATING
Establish what driving conditions caused the com-
plaint. Abnormal loads on the cooling system such as
the following may be the cause.
1. PROLONGED IDLE, VERY HIGH AMBI-
ENT TEMPERATURE, SLIGHT TAIL WIND AT
IDLE, SLOW TRAFFIC, TRAFFIC JAMS, HIGH
SPEED, OR STEEP GRADES:
Driving techniques that avoid overheating are:
•
Idle with A/C off when temperature gauge is at
end of normal range.
•
Increasing engine speed for more air flow is recom-
mended.
2. TRAILER TOWING:
Consult Trailer Towing section of owners manual.
Do not exceed limits.
3. AIR CONDITIONING; ADD-ON OR AFTER
MARKET:
A maximum cooling package should have been or-
dered with vehicle if add-on or after market A/C is
installed. If not, maximum cooling system compo-
nents should be installed for model involved per
manufacturer’s specifications.
4. RECENT SERVICE OR ACCIDENT RE-
PAIR:
Determine if any recent service has been performed
on vehicle that may effect cooling system. This may
be:
•
Engine adjustments (incorrect timing)
•
Slipping engine accessory drive belt(s)
•
Brakes (possibly dragging)
•
Changed parts (incorrect water pump rotating in
wrong direction)
•
Reconditioned radiator or cooling system refilling
(possibly under-filled or air trapped in system).
If investigation reveals none of the above as a
cause for engine overheating complaint, refer to fol-
lowing Symptom and Action chart.

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