JEEP CHEROKEE 1994 Service Repair Manual

REVERSE FLUSHING ENGINE
Drain the cooling system. Remove the thermostat
housing and thermostat. Install the thermostat hous-
ing. Disconnect the radiator upper hose from the ra-
diator and attach the flushing gun to the hose.
Disconnect the radiator lower hose from the water
pump. Attach a lead away hose to the water pump
inlet fitting.
CAUTION: On XJ models, be sure that the heater
control valve is closed (heat off). This is done to
prevent coolant flow with scale and other deposits
from entering the heater core.
Connect the water supply hose and air supply hose
to the flushing gun. Allow the engine to fill with wa-
ter. When the engine is filled, apply air in short
blasts, allowing the system to fill between air blasts.
Continue until clean water flows through the lead
away hose. For more information, refer to operating
instructions supplied with flushing equipment.
Remove the lead away hose, flushing gun, water
supply hose and air supply hose. Remove the thermo-
stat housing and install thermostat. Install the ther-
mostat housing with a replacement gasket. Refer to
Thermostat Replacement. Connect the radiator hoses.
Refill the cooling system with the correct antifreeze/
water mixture.
CHEMICAL CLEANING
In some instances, use a radiator cleaner (Mopar
Radiator Kleen or equivalent) before flushing. This
will soften scale and other deposits and aid the flush-
ing operation.
CAUTION: Be sure instructions on the container are
followed.
TESTING COOLING SYSTEM FOR LEAKS
ULTRAVIOLET LIGHT METHOD
All JeepŸ models have a leak detection additive
added to the cooling system before they leave the fac-
tory. The additive is highly visible under ultraviolet
light (black light). If the factory original coolant has
been drained, pour one ounce of additive into the
cooling system. The additive is available through the
part's department. Place the heater control unit in
HEAT position. Start and operate the engine until
the radiator upper hose is warm to the touch. Aim
the black light (tool 7138 or an equivalent), at the
components to be checked. If leaks are present, the
black light will cause the additive to glow a bright
green color.
The black light can be used along with a pressure
tester to determine if any external leaks exist (Fig.
19).
PRESSURE TESTER METHOD
The engine should be at the normal operating tem-
perature. Recheck the system cold if the cause of
coolant loss is not located during warm engine exam-
ination.
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING.
Carefully remove the radiator pressure cap from
the filler neck and check the coolant level. Push
down on the cap to disengage it from the stop tabs.
Wipe the inner part of the filler neck and examine
the lower inside sealing seat for nicks, cracks, paint,
dirt and solder residue. Inspect the reserve/overflow
tank tube for internal obstructions. Insert a wire
through the tube to be sure it is not obstructed.
Inspect the cams on the outside part of the filler
neck. If the cams are bent, seating of pressure cap
valve and tester seal will be affected. Bent cams can
be reformed if done carefully. Attach pressure tester
7700 or an equivalent to the radiator filler neck (Fig.
20).
Operate the tester pump to apply 124 kPa (18 psi)
pressure to the system. If the hoses enlarge exces-
sively or bulge while testing, replace as necessary.
Observe the gauge pointer and determine the condi-
tion of the cooling system according to the following
criteria:
²Holds Steady: If the pointer remains steady for two
minutes, there are no serious coolant leaks in the
system. However, there could be an internal leak
that does not appear with normal system test pres-
sure. Inspect for interior leakage or do the Internal
Fig. 19 Leak Detection Using Black LightÐTypical
7 - 18 COOLING SYSTEMJ

Leakage Test. Do this if it is certain that coolant is
being lost and no leaks can be detected.
²Drops Slowly: Shows a small leak or seepage is oc-
curring. Examine all connections for seepage or
slight leakage with a flashlight. Inspect the radiator,
hoses, gasket edges and heater. Seal any small leak
holes with a Sealer Lubricant or equivalent. Repair
leak holes and reinspect the system with pressure
applied.
²Drops Quickly: Shows that a serious leakage is oc-
curring. Examine the system for serious external
leakage. If no leaks are visible, inspect for internal
leakage. Large radiator leak holes should be repaired
by a reputable radiator repair shop.
INTERNAL LEAKAGE INSPECTION
Remove the oil pan drain plug and drain a small
amount of engine oil. Coolant, being heavier will
drain first, or operate engine to churn oil, then ex-
amine dipstick for water globules. Inspect the trans-
mission dipstick for water globules. Inspect the
transmission fluid cooler for leakage. Operate the en-
gine without the pressure cap on the radiator until
thermostat opens.
Attach a Pressure Tester to the filler neck. If pres-
sure builds up quickly, a leak exists as result of a
faulty cylinder head gasket or crack in the engine.
Repair as necessary.
WARNING: DO NOT ALLOW PRESSURE TO EX-
CEED 124 KPA (18 PSI). TURN THE ENGINE OFF.
TO RELEASE THE PRESSURE, ROCK THE TESTER
FROM SIDE TO SIDE. WHEN REMOVING THE
TESTER, DO NOT TURN THE TESTER MORE THAN
1/2 TURN IF THE SYSTEM IS UNDER PRESSURE.
If there is no immediate pressure increase, pump
the Pressure Tester until the indicated pressure is
within the system range. Vibration of the gauge
pointer indicates compression or combustion leakage
into the cooling system.WARNING: DO NOT DISCONNECT THE SPARK
PLUG WIRES WHILE THE ENGINE IS OPERATING.
CAUTION: Do not operate the engine with a spark
plug shorted for more than a minute. The catalytic
converter may be damaged.
Isolate the compression leak by shorting each
spark plug to the cylinder block. The gauge pointer
should stop or decrease vibration when spark plug
for leaking cylinder is shorted. This happens because
of the absence of combustion pressure.
COMBUSTION LEAKAGE TEST (WITHOUT
PRESSURE TESTER)
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
Drain sufficient coolant to allow for thermostat re-
moval. Refer to Thermostat Replacement. Disconnect
the water pump drive belt.
Disconnect the upper radiator hose from the ther-
mostat housing. Remove the housing and thermostat.
Install the thermostat housing.
Add coolant to the radiator to bring the level to
within 6.3 mm (1/4 in) of the top of the thermostat
housing.
CAUTION: Avoid overheating. Do not operate the
engine for an excessive period of time. Open the
draincock immediately after the test to eliminate
boil over of coolant.
Start the engine and accelerate rapidly three times
(to approximately 3000 rpm) while observing the
coolant. If internal engine combustion gases are leak-
ing into the cooling system, bubbles will appear in
the coolant. If bubbles do not appear, there is no in-
ternal combustion gas leakage.
COOLANT RESERVE/OVERFLOW SYSTEM
The system works along with the radiator pressure
cap. This is done by using thermal expansion and
contraction of the coolant to keep the coolant free of
trapped air. It provides:
²A volume for coolant expansion and contraction.
²A convenient and safe method for checking/adjust-
ing coolant level at atmospheric pressure. This is
done without removing the radiator pressure cap.
²Some reserve coolant to cover minor leaks and
evaporation or boiling losses.
Fig. 20 Pressurizing SystemÐTypical
JCOOLING SYSTEM 7 - 19

The coolant reserve/overflow system consists of a
radiator mounted pressurized cap, a plastic reserve/
overflow tank (Figs. 21, 22 or 23), a tube connecting
the radiator and tank, and an overflow tube on the
side of the tank.
TANK REMOVAL/INSTALLATION
(1) Remove the tube clamp at the tank and remove
tube.(2) On YJ models, remove the windshield washer
reservoir and its mounting bracket.
(3) Remove the tank mounting bolts and remove
tank.
(4) Reverse the preceding steps for installation.
RADIATOR PRESSURE CAP
All radiators are equipped with a pressure cap.
This cap releases pressure at some point within a
range of 83-110 kPa (12-16 psi). The pressure relief
point (in pounds) is engraved on top of the cap (Fig.
24).
The cooling system will operate at pressures
slightly above atmospheric pressure. This results in a
higher coolant boiling point allowing increased radi-
ator cooling capacity. The cap (Fig. 24) contains a
spring-loaded pressure relief valve. This valve opens
when system pressure reaches the release range of
83-110 kPa (12-16 psi).
A vent valve in the center of the cap allows a small
coolant flow through the cap when coolant is below
boiling temperature. The valve is completely closed
when boiling point is reached. As coolant cools, it
contracts and creates a vacuum in the cooling sys-
tem. This causes the vacuum valve to open and cool-
ant in reserve/overflow tank to be drawn through
connecting hose into radiator. If the vacuum valve is
stuck shut, radiator hoses will collapse on cool-down.
A rubber gasket seals the radiator filler neck. This
is done to maintain vacuum during coolant cool-down
and to prevent leakage when system is under pres-
sure.
Fig. 21 Reserve/Overflow TankÐYJ Models
Fig. 22 Reserve/Overflow TankÐXJ ModelsÐExcept
Right Hand Drive
Fig. 23 Reserve/Overflow TankÐXJ ModelsÐWith
Right Hand Drive
7 - 20 COOLING SYSTEMJ

RADIATOR CAP-TO-FILLER NECK
SEALÐPRESSURE RELIEF CHECK
With radiator cap installed on filler neck, remove
coolant reserve/ overflow tank hose from nipple on
filler neck. Connect a hand operated vacuum pump
to nipple. Operate pump until a reading of 47-to-61
kPa (14-to-18 in. Hg) appears on gauge. If the read-
ing stays steady, or drops slightly and then remains
steady, the pressure valve seal is good. Replace radi-
ator cap if reading does not hold.
WARNING: THE WARNING WORDS -DO NOT OPEN
HOT- ON THE RADIATOR PRESSURE CAP (FIG. 24)
ARE A SAFETY PRECAUTION. WHEN HOT, PRES-
SURE BUILDS UP IN COOLING SYSTEM. TO PRE-
VENT SCALDING OR INJURY, THE RADIATOR CAP
SHOULD NOT BE REMOVED WHILE THE SYSTEM
IS HOT AND/OR UNDER PRESSURE.
There is no need to remove the radiator capexcept
for the following purposes:
(1) To check and adjust antifreeze freeze point.
(2) To refill system with new antifreeze.
(3) For conducting service procedures.
(4) When checking for vacuum leaks.
WARNING: IF VEHICLE HAS BEEN RUN RECENTLY,
WAIT AT LEAST 15 MINUTES BEFORE REMOVING
RADIATOR CAP. WITH A RAG, SQUEEZE RADIA-TOR UPPER HOSE TO CHECK IF SYSTEM IS UN-
DER PRESSURE. PLACE A RAG OVER THE CAP
AND WITHOUT PUSHING DOWN, ROTATE CAP
COUNTER-CLOCKWISE TO THE FIRST STOP. AL-
LOW FLUID TO ESCAPE THROUGH OVERFLOW
HOSE INTO COOLANT RESERVE/OVERFLOW
TANK. SQUEEZE RADIATOR UPPER HOSE TO DE-
TERMINE WHEN PRESSURE HAS BEEN RE-
LEASED. WHEN COOLANT AND STEAM STOP
BEING PUSHED INTO TANK AND SYSTEM PRES-
SURE DROPS, REMOVE RADIATOR CAP COM-
PLETELY.
PRESSURE TESTING RADIATOR CAPS
Remove cap from radiator. Be sure that sealing
surfaces are clean. Moisten rubber gasket with water
and install the cap on pressure tester (tool 7700 or
an equivalent) (Fig. 25).
Operate the tester pump and observe the gauge
pointer at its highest point. The cap release pressure
should be 83-to-110 kPa (12-to-16 psi). The cap is sat-
isfactory when the pressure holds steady. It is also
good if it holds pressure within the 83-to-110 kPa
(12-to-16 psi) range for 30 seconds or more. If the
pointer drops quickly, replace the cap.
INSPECTION
Visually inspect the pressure valve gasket on the
cap. Replace cap if the gasket is swollen, torn or
worn. Inspect the area around radiator filler neck for
white deposits that indicate a leaking cap.
Fig. 24 Radiator Pressure Cap
Fig. 25 Pressure Testing Radiator Pressure Cap
JCOOLING SYSTEM 7 - 21

RADIATORS
GENERAL INFORMATION
All radiators are down flow types except XJ models
with 4.0L engines. Radiators in XJ models equipped
with the 4.0L six-cylinder engine, are the cross flow
type. Plastic tanks are used on all radiators.
CAUTION: Plastic tanks, while stronger than brass,
are subject to damage by impact, such as
wrenches.
If plastic tank has been damaged, plastic tank
and/or O-rings are available for service repair. Tank
replacement should be done by qualified personal
with proper equipment.
RADIATOR COOLANT FLOW CHECK
The following procedure will determine if coolant is
flowing through the cooling system.
If engine is cold, idle engine until normal operating
temperature is reached. Then feel the upper radiator
hose. If hose is hot, the thermostat is open and water
is circulating through cooling system.
RADIATOR REMOVAL/INSTALLATION
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS, RADIATOR CAP, OR
LOOSEN THE RADIATOR DRAINCOCK WITH THE
SYSTEM HOT AND PRESSURIZED. SERIOUS
BURNS FROM THE COOLANT CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUM-
BER 6094) (FIG. 26). SNAP-ON CLAMP TOOL (NUM-
BER HPC-20) MAY BE USED FOR LARGER
CLAMPS. ALWAYS WEAR SAFETY GLASSES
WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
XJ MODELS WITH 2.5L ENGINE
REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Observe the previousWARNINGS.Remove ra-
diator cap.(3) Position drain pan under draincock. Open radi-
ator draincock. Drain radiator.
(4) Remove radiator upper and lower hose clamps
and hoses.
(5) Remove alignment dowel E-clip from radiator
lower mounting bracket (Fig. 27).
(6) Disconnect coolant reserve/overflow tank hose
from radiator.
(7) Remove radiator fan shroud mounting bolts
(Fig. 28). Push shroud back against front of engine.
(8) If equipped, disconnect and plug automatic
transmission fluid cooler lines.
(9) Remove radiator top mounting bolts (Fig. 28).
(10) Remove the radiator grille mounting screws.
Remove grille (Fig. 29).
(11) Remove the air conditioning condenser-to-ra-
diator mounting bolt. Use an open end wrench to re-
Fig. 26 Hose Clamp ToolÐTypical
Fig. 27 Radiator Remove/InstallÐXJ ModelsÐ2.5L
Engine
7 - 22 COOLING SYSTEMJ

move bottom bolts (Fig. 30).
(12) Lift radiator straight up and out of vehicle.
Take care not to damage radiator fins.
INSTALLATION
(1) Install radiator behind air conditioning con-
denser with bottom alignment dowel inserted into ra-
diator lower mounting bracket.
(2) Install E-clip to alignment dowel.(3) Tighten the four condenser-to-radiator mount-
ing bolts to 6.2 Nzm (55 in. lbs.) torque.
(4) Install radiator grille.
(5) Tighten radiator top mounting bolts to 6 Nzm
(55 in. lbs.) torque.
(6) If equipped, connect automatic transmission
fluid cooler lines to radiator.
(7) Install the radiator fan shroud. Connect the
coolant reserve/overflow tank hose.
(8) Connect radiator hoses and install hose clamps.
(9) Connect negative battery cable.
(10) Close the draincock.
(11) Fill cooling system with correct coolant.
(12) Install radiator cap.
(13) Check and adjust automatic transmission fluid
level (if equipped).
XJ MODELS WITH 4.0L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
Fig. 28 Shroud Remove/InstallÐXJ Models With
2.5L Engine
Fig. 29 Grille Remove/InstallÐCherokee Models
With 2.5L Engine
Fig. 30 Condenser Mounting BoltsÐXJ Models With
2.5L Engine
JCOOLING SYSTEM 7 - 23

WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUM-
BER 6094) (FIG. 26). SNAP-ON CLAMP TOOL (NUM-
BER HPC-20) MAY BE USED FOR LARGER
CLAMPS. ALWAYS WEAR SAFETY GLASSES
WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Observe the previousWARNINGS.
(3) Remove pressure cap.
(4) For access to radiator draincock, remove radia-
tor grille (Fig. 29).
(5) Attach one end of a 24 inch long X 1/4 inch ID
hose to the radiator draincock. Put the other end into
a clean container. Open draincock and drain radia-
tor.
(6) If equipped, disconnect electric cooling fan elec-
trical connector (Fig. 31).
(7) Remove electric fan mounting bolts. Lift fan
straight up and out of engine compartment.
(8) Remove the mechanical (non-electrical) fan
shroud mounting bolts. Lift shroud up until align-ment tabs at the bottom are clear of slots in bracket
at bottom of radiator (Fig. 32). Place shroud over me-
chanical fan.
(9) If equipped, disconnect and plug automatic
transmission fluid cooler lines. If equipped with re-
mote cooler, remove line to cooler from bracket at
bottom of radiator.
(10) Disconnect radiator upper and lower hoses.
(11) Mark the position of the hood latch striker on
the radiator crossmember and remove hood latch
striker.
(12) Remove radiator upper crossmember bracket.
(13) Remove radiator upper crossmember.
(14) If equipped with air conditioning, separate ra-
diator from condenser by removing condenser-to-radi-
ator mounting brackets (Fig. 33).
(15) Lift radiator straight up and out of engine
compartment taking care not to damage fins.
INSTALLATION
The radiator has two alignment dowels. They are
located on the bottom tank and fit into rubber grom-
mets in the radiator lower crossmember.
(1) Lower radiator into engine compartment. Posi-
tion alignment dowels into grommets in radiator
lower crossmember (Fig. 34).
(2) If equipped with air conditioning, attach con-
denser to radiator with mounting brackets (Fig. 33).
(3) Install radiator upper crossmember.
(4) Install radiator upper crossmember bracket.
(5) Install hood latch striker.
(6) Connect radiator upper and lower hoses.
Fig. 31 Auxiliary FanÐRemove/Install
Fig. 32 Auxiliary Fan and Mechanical Fan
ShroudÐRemove/InstallÐTypical
7 - 24 COOLING SYSTEMJ

(7) If equipped, connect automatic transmission
fluid cooler lines. If equipped with remote cooler, at-
tach cooler line to bracket at bottom of radiator.
(8) Install electric cooling fan (if equipped). Insert
alignment tabs at bottom of fan shroud into slots in
bracket at bottom of radiator. Tighten mounting
bolts to 4 Nzm (36 in. lbs.) torque.
(9) Connect electric cooling fan electrical connec-
tor.(10) Install mechanical cooling fan shroud. Insert
alignment tabs at bottom of shroud into slots in
bracket at bottom of radiator. Tighten mounting
bolts to 4 Nzm (36 in. lbs.) torque (Fig. 32).
(11) Close radiator draincock.
(12) Install grille.
(13) Connect negative battery cable.
(14) Fill cooling system with correct coolant. Refer
to the Coolant section of this group.
(15) Install pressure cap.
(16) Check and adjust automatic transmission fluid
level (if equipped).
YJ MODELS
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUM-
BER 6094) (FIG. 26). SNAP-ON CLAMP TOOL (NUM-
BER HPC-20) MAY BE USED FOR LARGER
CLAMPS. ALWAYS WEAR SAFETY GLASSES
WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
REMOVAL
(1) Disconnect negative battery cable at battery.
(2) Observe the previousWARNINGS.Remove
the radiator cap.
(3) Position drain pan under draincock. Open radi-
ator draincock and drain radiator.
(4) Remove radiator upper and lower hose clamps
and hoses.
(5) Disconnect coolant reserve/overflow tank hose
from radiator.
(6) Remove fan shroud bolts and push shroud back
onto fan (Fig. 35).
(7) If equipped, disconnect and plug automatic
transmission fluid cooler lines.
(8) Remove radiator attaching bolts.
(9) Lift radiator straight up and out of vehicle tak-
ing care not to damage radiator fins.
Fig. 33 Condenser-to-Radiator Mounting
BracketsÐXJ with 4.0L Engine
Fig. 34 Radiator InstallationÐXJ Models with 4.0L
Engine
JCOOLING SYSTEM 7 - 25

INSTALLATION
(1) Install the radiator. Tighten the mounting bolts
to8Nzm (6 ft. lbs.) torque (Fig. 35).
(2) Close radiator draincock.
(3) Install fan shroud. Tighten mounting bolts to
16 Nzm (11 ft. lbs.) torque.
(4) If equipped, remove plugs and connect auto-
matic transmission fluid cooler lines.
(5) Connect radiator hoses and install hose clamps.
(6) Connect negative battery cable.
(7) Fill cooling system with correct coolant. Refer
to the Coolant section of this group.
(8) Connect reserve/overflow tank hose.
(9) Install radiator cap.
(10) Check and adjust automatic transmission fluid
level (if equipped).
COOLING SYSTEM HOSES
Rubber hoses route coolant to and from the radia-
tor, intake manifold and heater core. All XJ models
equipped with air conditioning have a coolant control
valve. This is located in-line with the heater core in-
let and outlet hoses. It controls coolant flow to the
heater core when the air conditioning system is in
operation.
Radiator lower hoses are spring-reinforced to pre-
vent collapse from water pump suction at moderate
and high engine speeds.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUM-
BER 6094) (FIG. 36). SNAP-ON CLAMP TOOL (NUM-
BER HPC-20) MAY BE USED FOR LARGER
CLAMPS. ALWAYS WEAR SAFETY GLASSES
WHEN SERVICING CONSTANT TENSION CLAMPS.CAUTION: A number or letter is stamped into the
tongue of constant tension clamps. If replacement
is necessary, use only an original equipment clamp
with matching number or letter.
Inspect the hoses at regular intervals. Replace
hoses that are cracked, feel brittle when squeezed, or
swell excessively when the system is pressurized.
For all vehicles: In areas where specific routing
clamps are not provided, be sure that hoses are posi-
tioned with sufficient clearance. Check clearance
from exhaust manifolds and pipe, fan blades, drive
belts and sway bars. Improperly positioned hoses can
be damaged, resulting in coolant loss and engine
overheating.
Ordinary worm gear type hose clamps (when
equipped) can be removed with a straight screw-
driver or a hex socket.To prevent damage to
hoses or clamps, the hose clamps should be
tightened to 4 Nzm (34 in. lbs.) torque. Do not
over tighten hose clamps.
When performing a hose inspection, inspect the ra-
diator lower hose for proper position and condition of
the internal spring.
COOLING SYSTEM FANS
All models are equipped with a mechanical temper-
ature controlled fan. The viscous fan drive is a
torque-and-temperature-sensitive clutch unit. It auto-
matically increases or decreases fan speed to provide
proper engine cooling. XJ models equipped with a
4.0L engine may also have an auxiliary electrical
fan. This is with models that have air conditioning
and/or heavy duty cooling.
VISCOUS FAN DRIVE OPERATION
The viscous fan drive (Fig. 37) is a silicone-fluid-
filled coupling. On some engines it connects the fan
assembly to the fan/water pump pulley. The coupling
allows the fan to be driven in a normal manner. This
is done at low engine speeds while limiting the top
Fig. 35 RadiatorÐRemove/InstallÐYJ Models
Fig. 36 Hose Clamp ToolÐTypical
7 - 26 COOLING SYSTEMJ

speed of the fan to a predetermined maximum level
at higher engine speeds. A bimetallic spring coil is
located on the front face. This spring coil reacts to
the temperature of the radiator discharge air. It en-
gages the viscous fan drive for higher fan speed if
the air temperature from the radiator rises above a
certain point. Until additional engine cooling is nec-
essary, the fan will remain at a reduced rpm regard-
less of engine speed.
Only when sufficient heat is present, will the vis-
cous fan drive engage. This is when the air flowing
through the radiator core causes a reaction from the
bimetallic coil. It then increases fan speed to provide
the necessary additional engine cooling.
Once the engine has cooled, the radiator discharge
temperature will drop. The bimetallic coil again re-
acts and the fan speed is reduced to the previous dis-
engaged speed.
CAUTION: Engines equipped with serpentine drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheat-
ing.
VISCOUS FAN DRIVE TEST
The cooling system must be in good condition. This
is checked prior to performing the following test. It
also will ensure against excessively high coolant
temperature.
CAUTION: Be sure that there is adequate fan blade
clearance before drilling.(1) Drill a 3.18-mm (1/8-in) diameter hole in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18É-to-
105ÉC (0É-to-220É F). Insert thermometer through the
hole in the shroud. Be sure that there is adequate
clearance from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light (timing light is to be used as a strobe
light).
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator (or air con-
ditioner condenser). Use tape at the top to secure the
plastic and be sure that the air flow is blocked.
(5) Be sure that the air conditioner (if equipped) is
turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A DI-
RECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm with
the timing light (strobe light) aimed at the fan
blades. Within ten minutes the air temperature (in-
dicated on the dial thermometer) should be 88É C
(190É F). Satisfactory operation of the fan drive re-
quires that it engage before or at 88É C (190É F). En-
gagement is distinguishable by a definite increase in
flow noise. The timing light also will indicate an in-
crease in the speed of the fan.
(7) When the air temperature reaches 88É C (190É
F), remove the plastic sheet. Satisfactory operation of
the viscous fan requires the air temperature to drop
20É F (11É C) or more. A definite decrease of audible-
fan-air-flow-noise should be noticed. Replace defec-
tive fan assemblies.
VISCOUS FAN DRIVE REPLACEMENT
REMOVAL
Some engines have the mechanical fan/viscous fan
drive assembly mounted directly to the water pump
hub (Fig. 38). It may also be mounted to a hub/bear-
ing attached to an aluminum bracket on the right
front side of engine (Fig. 39).
(1) Loosen but do not remove at this time, the four
fan hub mounting nuts (Figs. 38 or 39).
(2) Remove accessory serpentine drive belt. Refer
to Belt Service in the Engine Accessory Drive Belt
section of this group.
(3) Some models with certain engines may require
the removal of the fan shroud to remove the viscous
fan drive. The fan shroud and fan blade/viscous fan
drive should be removed from the vehicle as one as-
sembly.
Fig. 37 Viscous Fan DriveÐTypical
JCOOLING SYSTEM 7 - 27