sensor JEEP CHEROKEE 1994 Service Workshop Manual

Clean the reservoir and caps thoroughly before
checking level or adding fluid. Cap open lines and
hoses during service to prevent dirt entry.
Dirt or foreign material entering the ABS hydrau-
lic system through the reservoir opening will circu-
late within the system. The result will be poor brake
performance and possible component failure. Use
clean, fresh fluid only to top off, or refill the system.
WHEEL SENSOR AIR GAP ADJUSTMENT
Only rear sensor air gap is adjustable. The front
sensors are fixed and cannot be adjusted.
A rear sensor air gap adjustment is only
needed when reinstalling an original sensor. Re-
placement sensors have an air gap spacer at-
tached to the sensor pickup face. The spacer
establishes correct air gap when pressed against
the tone ring during installation. As the tone
ring rotates, it peels the spacer off the sensor to
create the required air gap.
Preferred rear sensor air gap is 1.1 mm (0.043 in.).
Acceptable air gap range is 0.92 to 1.275 mm (0.036
to 0.050 in.).
Front sensor air gap is not adjustable. The front
sensors are fixed in position and cannot be adjusted.
Front sensor air gap can only be checked. Air gap
should be 0.040 to 1.3 mm (0.0157 to 0.051 in.). If
front sensor air gap is incorrect, the sensor is either
loose, or damaged.
FRONT WHEEL SENSOR REMOVAL
(1) Raise vehicle and turn wheel outward for eas-
ier access to sensor.
(2) Remove sensor wire from mounting brackets.
(3) Clean sensor and surrounding area before removal.
(4) Remove bolt attaching sensor to steering
knuckle and remove sensor.
(5) Unseat grommet retaining sensor wire in wheel
house panel.
(6) In engine compartment, disconnect sensor wire con-
nector at harness plug. Then remove sensor and wire.
FRONT WHEEL SENSOR INSTALLATION
(1) Apply Mopar Lock N' Seal or Loctite 242 to
bolt that attaches sensor to steering knuckle. Use
new sensor bolt if original bolt is worn or damaged.
(2) Position sensor on steering knuckle. Seat sen-
sor locating tab in hole in knuckle and install sensor
attaching bolt finger tight.
(3) Tighten sensor bolt to 14 NIm (11 ft. lbs.) torque.
(4) Attach sensor wire to steering knuckle bracket
with grommets on sensor wire.
(5) Route sensor wire forward and behind shock
absorber. Then attach sensor wire to spring seat
bracket with grommets on sensor wire.
(6) Route sensor wire to outer sill bracket. Remove
all twists or kinks from wire.(7) Attach sensor wire to sill bracket with grom-
met. Be sure wire is free of twists and kinks.
(8) Verify sensor wire routing. Wire should loop
forward and above sill bracket. Loose end of wire
should be below sill bracket and towards brake hose.
(9) Seat sensor wire grommet in body panel and
clip wire to brake line at grommet location.
(10) Connect sensor wire to harness in engine com-
partment.
REAR WHEEL SENSOR REMOVAL
(1) On XJ models, if separate connectors are not
used to attach sensor harness to each sensor wire,
proceed as follows:
(a) Raise and fold rear seat forward for access to
rear sensor connectors (Figs. 4 and 5).
(b) Disconnect sensors at rear harness connectors.
(c) Push sensor grommets and sensor wires
through floorpan.
Fig. 4 Acceleration Switch And Rear Sensor
Connections (XJ)
Fig. 5 Rear Sensor Connections (XJ)
JABS COMPONENT SERVICE 5 - 49

(2) Raise vehicle.
(3) Disconnect sensor wires at rear axle connectors.
(4) Remove wheel and tire assembly.
(5) Remove brake drum.
(6) Remove clips securing sensor wires to brake
lines or rear axle and rear brake hose.
(7) Unseat sensor support plate grommet.
(8) Remove bolt attaching sensor to bracket and
remove sensor.
REAR WHEEL SENSOR INSTALLATION
(1) Insert sensor wire through support plate hole
and seat sensor grommet in support plate.
(2) Apply Mopar Lock N' Seal or Loctite 242 to
original sensor bolt. Use new bolt if original is worn
or damaged.
(3) Install sensor bolt finger tight only at this
time.
(4) Set sensor air gap as follows:
(a) Iforiginal sensoris being installed, remove
any remaining pieces of cardboard spacer from sen-
sor pickup face. Then adjust air gap to preferred
setting of 1.1 mm (0.043 in.) with brass feeler
gauge (Fig. 6). Tighten sensor bolt to 11 Nzm (11 ft.
lbs.) torque.
(b) Ifnew sensoris being installed, push card-
board spacer on sensor face (Fig. 7) against tone
ring. Then tighten sensor bolt to 8 Nzm (6 ft. lbs.)
torque. Correct air gap will be established as tone
ring rotates and peels spacer off sensor face.
(c) Verify sensor air gap adjustment. If adjust-
ment changed after tightening bolt, readjust sensor
air gap as needed.
(5) On YJ, connect rear sensor wires to connectors
at axle. On XJ, route sensor wires to rear seat area.
(6) Feed sensor wires through floorpan access hole
and seat sensor grommets in floorpan.
(7) Verify that rear sensor wire are secured to rear
brake hose and axle with clips. Verify that wire is
clear of rotating components.
(8) Install brake drum and wheel.
(9) Lower vehicle.
(10) On XJ, connect sensor wire to harness connec-
tor. Then reposition carpet and fold rear seat down.
MASTER CYLINDER REMOVAL
(1) Disconnect pedal travel sensor wires.
(2) Remove air cleaner and hoses on XJ models.
(3) Remove clamps that secure reservoir hoses to
HCU pipes.
(4) Position small drain container under master
cylinder reservoir. Remove reservoir hoses from HCU
pipes and allow fluid to drain into container before
removing reservoir. Discard fluid drained from reser-
voir.
(5) Pump brake pedal to exhaust all vacuum from
power brake booster.
(6) Disconnect necessary brakelines at master cyl-
inder and combination valve. Also remove combina-
tion valve bracket bolt.
(7) Remove nuts attaching master cylinder to
booster mounting studs.
(8) Remove master cylinder. Pull cylinder forward
and off studs. Then work cylinder past combination
valve, brakelines, pedal travel sensor and out of en-
gine compartment.
MASTER CYLINDER INSTALLATION
(1) If new master cylinder is being installed, bleed
cylinder on bench before installing it in vehicle.
(2) Work master cylinder into position and install
it in booster. Be sure cylinder is properly seated on
booster studs. Also be sure booster-to-cylinder seal is
not displaced during installation.
(3) Connect reservoir hoses to HCU pipes.
(4) Verify that master cylinder and booster are
properly connected.
(5) Install and tighten master cylinder attaching
nuts to 34 Nzm (25 ft. lbs.) torque.
(6) Connect brakelines to master cylinder.
(7) Install combination valve, if removed and in-
stall bolt that secures valve bracket to master cylin-
der.
(8) Connect sensor wires.
Fig. 6 Setting Air Gap On Original Rear Sensor
Fig. 7 New Rear Sensor With Air Gap Spacer
5 - 50 ABS COMPONENT SERVICEJ

(9) Fill reservoir and bleed brakes. Refer to proce-
dure in this section.
(10) Install air cleaner and hoses.
PEDAL TRAVEL SENSOR SERVICE
CAUTION: The pedal travel sensor and booster
must form a matched set. The cap on the sensor
plunger and booster shell are color coded for iden-
tification, and to ensure they are used as matched
sets. Be sure the color of the sensor cap and the
color dot on the booster shell are the same before
installation. Refer to the Sensor Replacement infor-
mation before installing a new or original sensor.
PEDAL TRAVEL SENSOR REMOVAL
(1) Disconnect wires at sensor.
(2) Pump brake pedal to exhaust all vacuum from
booster.
(3) Unseat sensor retaining ring.
(4) Remove sensor from booster (Fig. 8).
PEDAL TRAVEL SENSOR REPLACEMENT
A new pedal travel sensor is supplied with four dif-
ferent color caps. The caps are color coded to ease
matching them with the color code dot on the booster
shell.
Compare the color of the new sensor cap and the
color dot on the booster shell. If the colors match,
proceed with sensor installation. However, if the col-
orsdo not match, select and install the correct color
cap on the sensor plunger before proceeding.
PEDAL TRAVEL SENSOR INSTALLATION
(1) Check color dot on face of brake booster. Then
check color of cap on sensor plunger. If colors match,
proceed with installation. If colors do not match, in-
stall correct color cap on end of plunger.
(2) Install O-ring on sensor.
(3) Install sensor retaining ring on booster flange.
(4) Insert sensor in retaining ring and booster.
(5) Verify that retaining ring is properly engaged
in sensor and that sensor is seated in booster.
(6) Connect wires to sensor.
(7) Check sensor operation with DRB II scan tool.
POWER BRAKE BOOSTER REMOVAL
(1) Pump brake pedal until all vacuum is ex-
hausted from power brake booster.
(2) Disconnect pedal travel sensor.
(3) Remove air cleaner and hoses.
(4) Remove clamps that secure reservoir hoses to
HCU pipes. Then remove hoses from pipes.
(5) Disconnect brakelines at master cylinder.
(6) Remove combination valve bracket bolt if nec-
essary.
(7) Remove nuts attaching master cylinder to
booster mounting studs.(8) Remove master cylinder. Pull cylinder forward
and off studs. Then work cylinder past combination
valve, brakelines, pedal travel sensor and out of en-
gine compartment.
(9) Disconnect vacuum hose at booster check valve.
(10) Disconnect booster push rod from brake pedal.
(11) Remove nuts attaching booster to passenger
compartment side of dash panel.
(12) Slide booster forward and work it out of en-
gine compartment.
POWER BRAKE BOOSTER INSTALLATION
(1) Position booster on dash panel. Align booster
mounting studs with holes in panel and seat booster
(Fig. 9).
(2) In passenger compartment, install booster at-
taching nuts on mounting studs. Tighten attaching
nuts to 41 Nzm (30 ft. lbs.) torque.
(3) Install seal on master cylinder. Seal is slight
interference fit to help hold it in place.
Fig. 8 Pedal Travel Sensor Mounting
Fig. 9 Booster Attachment At Dash PanelÐYJ
Shown
JABS COMPONENT SERVICE 5 - 51

CAUTION: The pedal travel sensor and booster
must form a matched set. The cap on the sensor
plunger and the color dot on the booster shell are
color coded for identification, and to ensure they
are used as matched sets. Be sure the color on the
sensor cap and booster shell are the same before
installation. Refer to the Sensor Replacement infor-
mation before installing a new or original sensor.
(4) If new pedal travel sensor is being installed in
original booster, compare color dot on booster shell with
color of cap on sensor (Fig. 10). If both are same color,
proceed with installation. However, if colorsdo not
match, select correct color cap from kit supplied with
new sensor and install it on end of sensor plunger.
(5) Install O-ring on pedal travel sensor.
(6) Install sensor retaining ring on booster flange.
Be sure retaining ring is firmly seated.
(7) Insert sensor into booster. Be sure sensor is
fully seated and engaged in retaining ring.
(8) Connect booster push rod to brake pedal.
(9) Attach vacuum hose to booster check valve.
(10) Install master cylinder on booster. Tighten
cylinder attaching nuts to 25-30 Nzm (220-267 in.
lbs.) torque.
(11) Connect brakelines to master cylinder.
(12) Install combination valve bracket bolt if re-
moved.
(13) Connect reservoir hoses to HCU pipes.
(14) Connect sensor wires.
(15) Bleed brakes. Refer to procedure in this section.
(16) Install air cleaner and hoses.
ACCELERATION SENSOR REMOVAL
(1) On XJ models, tilt rear seat assembly forward
for access to sensor (Fig. 11).
(2) On YJ models, move driver seat forward or
rearward for access to sensor and mounting bracket
(Fig. 11).
(3) Disconnect sensor harness (Fig. 10).
(4) On XJ models, remove screws attaching sensor
to bracket. Then remove sensor.
(5) On YJ models, remove screws attaching sensor
bracket to floorpan. Then remove sensor from bracket.
ACCELERATION SENSOR INSTALLATION
(1) Note position of locating arrow on sensor. Sen-
sor must be positioned so arrow faces forward.
CAUTION: The sensor mercury switch will not func-
tion properly if the sensor is mispositioned. Verify
that the sensor locating arrow is pointing to the
front of the vehicle.
(2) Position sensor in mounting bracket (Fig. 10).
(3) Install and tighten sensor attaching screws to
2-4 Nzm (17-32 in. lbs.) torque.
(4) Connect harness to sensor. Be sure harness
connecter is firmly seated.
(5) Move seat back to normal position.
Fig. 10 Booster Push Rod And Pedal Travel Sensor
Fig. 11 Acceleration Sensor Mounting
5 - 52 ABS COMPONENT SERVICEJ

(5) Mark or tag HCU hydraulic lines for assembly
reference.
(6) Disconnect hydraulic lines at HCU.
(7) Move HCU harness and air cleaner hose pipe
aside for access to HCU bracket nuts.
(8) Remove single bolt and two nuts attaching
HCU to mounting bracket on inner fender panel
(Figs. 16 and 17).
(9) Remove HCU. Lift HCU up and off mounting
bracket studs. Then work HCU past brakelines and
master cylinder to remove it.
HCU INSTALLATIONÐXJ
(1) Connect master cylinder reservoir hoses to
HCU pipes.
(2) Position HCU assembly on mounting bracket
and install attaching nuts.(3) Connect hydraulic lines to HCU (Fig. 18). Line
fitting nuts and bosses on valve body ports are color
coded. Be sure lines are properly connected.
(4) Connect HCU harness wires to HCU.
(5) Check routing of HCU lines/hoses. Be sure
lines are not kinked and are clear of engine compo-
nents.
(6) Fill master cylinder reservoir with Mopar DOT
3 brake fluid or equivalent.
(7) Bleed brake system.
(8) Install air cleaner and hoses. Secure air cleaner
hose pipe to fender apron with clamp.
(9) Check brake pedal action. Bleed brakes again if
pedal is not firm (feels soft/spongy).
HCU REMOVALÐYJ
(1) Place shop towels or small container under
master cylinder reservoir hoses.
(2) Disconnect master cylinder reservoir hoses at
HCU.
(3) Disconnect all sensor and harness wires at
HCU.
(4) Disconnect brakelines at HCU (Fig. 19). Mark
or tag lines for installation reference.
(5) Remove bolt and nuts attaching HCU mount-
ing bracket to fender apron and remove HCU.
HCU INSTALLATIONÐYJ
(1) Position HCU on fender apron (Figs. 2 and 19)
and install attaching bolts/nuts.
(2) Connect brakelines to HCU.
(3) Connect harness and sensor wires to HCU.
(4) Connect master cylinder reservoir hoses to
HCU.
Fig. 16 HCU Mounting (Left Hand Drive XJ)
Fig. 17 HCU Mounting (Right Hand Drive XJ)
Fig. 18 HCU Hydraulic Line Connections
5 - 54 ABS COMPONENT SERVICEJ

(5) Fill and bleed brake system.
COMBINATION VALVE REPLACEMENTÐXJ
The combination valve is not a repairable compo-
nent. The valve is serviced as an assembly whenever
diagnosis indicates replacement is necessary.
(1) Remove air cleaner housing for access to valve,
if necessary.
(2) Remove bolt attached valve to master cylinder
(Fig. 20).
(3) Disconnect pedal travel sensor harness connec-
tor and move harness wires aside for working access
if necessary.
(4) Disconnect pressure differential switch wires at
valve.
(5) Disconnect hydraulic lines at valve and remove
valve from vehicle.
(6) Connect hydraulic lines to valve.
(7) Position valve bracket on master cylinder and
install bracket attaching bolt.(8) Reconnect pressure differential switch and
pedal travel sensor wires.
(9) Bleed brake system. Refer to procedure in this
section.
COMBINATION VALVE REPLACEMENTÐYJ
The combination valve mounting bracket is perma-
nently attached to the valve. The bracket and valve
are serviced as an assembly.
(1) Disconnect harness wires from combination
valve switch.
(2) Disconnect brakelines attached to combination
valve.
(3) Remove nuts attaching combination valve
bracket to master cylinder mounting studs (Fig. 19).
(4) Remove valve and bracket as assembly.
(5) Start all brakelines in combination valve by
hand. Tighten line fittings just enough to prevent
leaks.
(6) Position valve mounting bracket on studs.
(7) Install and tighten nuts that attach combina-
tion valve bracket to studs on power brake booster.
(8) Connect wires to combination valve switch.
(9) Fill and bleed brake system.
(10) Final-tighten brakeline fittings to 18-23 Nzm
(160-210 in. lbs.) torque after bleeding brakes.
Fig. 19 HCU Mounting (YJ)
Fig. 20 Combination Valve Mounting (XJ)
JABS COMPONENT SERVICE 5 - 55

CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
ON-BOARD DIAGNOSTICS
XJ and YJ models are equipped with On-Board Di-
agnostics for certain cooling system components. Re-
fer to On-Board Diagnostics (OBD) in the Diagnosis
section of this group for additional information. If the
powertrain control module (PCM) detects low engine
coolant temperature, it will record a Diagnostic Trou-
ble Code (DTC) in the PCM memory. The DTC num-
ber for low coolant temperature is 17. Do not change
a thermostat for lack of heat as indicated by the in-
strument panel gauge or heater performance unless a
DTC number 17 is present. Refer to the Diagnosis
section of this group for other probable causes. For
other DTC numbers, refer to On-Board Diagnostics
in the General Diagnosis section of group 14, Fuel
Systems.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
REMOVAL
WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Drain the coolant from the radiator until the
level is below the thermostat housing.
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. 14). 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.
(2) Remove radiator upper hose and heater hose at
thermostat housing.
(3) Disconnect wiring connector at engine coolant
temperature sensor.(4) Remove thermostat housing mounting bolts,
thermostat housing, gasket and thermostat (Fig. 15).
Discard old gasket.
(5) Clean the gasket mating surfaces.
INSTALLATION
(1) Install the replacement thermostat so that the
pellet, which is encircled by a coil spring, faces the
engine. All thermostats are marked on the outer
flange to indicate the proper installed position.
(a) Observe the recess groove in the engine cyl-
inder head (Fig. 16).
(b) Position thermostat in groove with arrow and
air bleed hole on outer flange pointing up.
(2) Install replacement gasket and thermostat
housing.
Fig. 14 Hose Clamp ToolÐTypical
Fig. 15 Thermostat Removal/Installation
7 - 14 COOLING SYSTEMJ

CAUTION: Tightening the thermostat housing un-
evenly or with the thermostat out of its recess, may
result in a cracked housing.
(3) Tighten the housing bolts to 20 Nzm (15 ft. lbs.)
torque.
(4) Install hoses to thermostat housing.
(5) Install electrical connector to coolant tempera-
ture sensor.
(6) Be sure that the radiator draincock is tightly
closed. Fill the cooling system to the correct level
with the required coolant mixture. Refer to Refilling
Cooling System in this group.
(7) Start and warm the engine. Check for leaks.
COOLANT
GENERAL INFORMATION
The cooling system is designed around the coolant.
Coolant flows through the engine water jackets ab-
sorbing heat produced during engine operation. The
coolant carries heat to the radiator and heater core.
Here it is transferred to the ambient air passing
through the radiator and heater core fins. The cool-
ant also removes heat from the automatic transmis-
sion fluid in vehicles equipped with an automatic
transmission.
COOLANT PERFORMANCE
The required ethylene-glycol (antifreeze) and water
mixture depends upon climate and vehicle operating
conditions. The coolant performance of various mix-
tures follows:
Pure Water-Water can absorb more heat than a
mixture of water and ethylene-glycol. This is for pur-pose of heat transfer only. Water also freezes at a
higher temperature and allows corrosion.
100 percent Ethylene-Glycol-The corrosion inhib-
iting additives in ethylene-glycol need the presence
of water to dissolve. Without water, additives form
deposits in system. These act as insulation causing
temperature to rise to as high as 149ÉC (300ÉF). This
temperature is hot enough to melt plastic and soften
solder. The increased temperature can result in en-
gine detonation. In addition, 100 percent ethylene-
glycol freezes at -22ÉC (-8ÉF).
50/50 Ethylene-Glycol and Water-Is the recom-
mended mixture, it provides protection against freez-
ing to -37ÉC (-35ÉF). The antifreeze concentration
must alwaysbe a minimum of 44 percent, year-
round in all climates. If percentage is lower, engine
parts may be eroded by cavitation. Maximum protec-
tion against freezing is provided with a 68 percent
antifreeze concentration, which prevents freezing
down to -67.7ÉC (-90ÉF). A higher percentage will
freeze at a warmer temperature. Also, a higher per-
centage of antifreeze can cause the engine to over-
heat because specific heat of antifreeze is lower than
that of water.
CAUTION: Richer antifreeze mixtures cannot be
measured with normal field equipment and can
cause problems associated with 100 percent ethyl-
ene-glycol.
COOLANT SELECTION-ADDITIVES
Coolant should be maintained at the specified level
with a mixture of ethylene glycol-based antifreeze
and low mineral content water. Only use an anti-
freeze containing ALUGARD 340-2 Ÿ.
CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
COOLANT SERVICE
It is recommended that the cooling system be
drained and flushed at 84,000 kilometers (52,500
miles), or 3 years, whichever occurs first. Then every
two years, or 48,000 kilometers (30,000 miles),
whichever occurs first.
COOLANT LEVEL CHECKÐROUTINE
Do not remove radiator cap for routine coolant
level inspections. The coolant level can be
checked at coolant reserve/overflow tank.
The coolant reserve/overflow system provides a
quick visual method for determining coolant level
without removing radiator pressure cap. With engine
idling and at normal operating temperature, observe
coolant level in reserve/overflow tank. The coolant
level should be between ADD and FULL marks.
Fig. 16 Thermostat Recess
JCOOLING SYSTEM 7 - 15

ADDING ADDITIONAL COOLANTÐROUTINE
Do not remove radiator cap to add coolant to
system.When adding coolant to maintain correct
level, do so at coolant reserve/overflow tank. Use a
50/50 mixture of ethylene-glycol antifreeze contain-
ing Alugard 340-2 Ÿ and low mineral content water.
Remove radiator cap only for testing or when refill-
ing system after service. Removing cap unnecessarily
can cause loss of coolant and allow air to enter sys-
tem, which produces corrosion.
COOLANT LEVEL CHECK-SERVICE
The cooling system is closed and designed to main-
tain coolant level to top of radiator.
WARNING: DO NOT OPEN RADIATOR DRAINCOCK
WITH ENGINE RUNNING OR WHILE ENGINE IS HOT
AND COOLING SYSTEM IS UNDER PRESSURE.
When vehicle servicing requires a coolant level
check in radiator, drain several ounces of coolant
from radiator drain cock. Do this while observing
coolant reserve/overflow system tank. The coolant
level in reserve/overflow tank should drop slightly. If
not, inspect for a leak between radiator and coolant
reserve/overflow system connection. Remove radiator
cap. The coolant level should be to top of radiator. If
not and if coolant level in reserve/overflow tank is at
ADD mark, check for:
²An air leak in coolant reserve/overflow tank or its
hose
²An air leak in radiator filler neck
²Leak in pressure cap seal to radiator filler neck
LOW COOLANT LEVEL-AERATION
If the coolant level in radiator drops below top of
radiator core tubes, air will enter cooling system.
Low coolant level can cause thermostat pellet to be
suspended in air instead of coolant. This will cause
thermostat to open later, which in turn causes higher
coolant temperature. Air trapped in cooling system
also reduces amount of coolant circulating in heater
core resulting in low heat output.
DEAERATION
As the engine operates, any air trapped in cooling
system gathers under the radiator cap. The next time
the engine is operated, thermal expansion of coolant
will push any trapped air past radiator cap into the
coolant reserve/overflow tank. Here it escapes to the
atmosphere into the tank. When the engine cools
down the coolant, it will be drawn from the reserve/
overflow tank into the radiator to replace any re-
moved air.
DRAINING COOLING SYSTEM
ALL MODELSÐEXCEPT XJ WITH 4.0L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
DO NOT remove the radiator cap when draining
the coolant from the reserve/overflow tank. Open the
radiator draincock and when the tank is empty, re-
move the radiator cap. The coolant does not have to
be removed from the tank unless the system is being
refilled with a fresh mixture.
(1) Drain the coolant from the radiator by loosen-
ing the draincock.
(2) Drain coolant from engine as follows:
(a) On 2.5L engines (all models) by removing
drain plug at left rear side of block.
(b) On 4.0L engines by removing the drain plug
or coolant temperature sensor on the left side of
the block (Fig. 17).
XJ MODELS WITH 4.0L ENGINE
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH SYSTEM HOT AND UNDER
PRESSURE. SERIOUS BURNS FROM COOLANT
CAN OCCUR.
Fig. 17 Draining CoolantÐ4.0L Engine
7 - 16 COOLING SYSTEMJ

DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Remove radiator pressure cap.
(2) For access to radiator draincock, remove radia-
tor grille (Fig. 18).
(3) 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 coolant
from radiator.
(4) Drain coolant from engine by removing the
drain plug and coolant temperature sensor on left
side of block (Fig. 17).
REFILLING COOLING SYSTEM
YJ MODELS
(1) Remove draining hose. Tighten the radiator
draincock and the cylinder block drain plug(s).
(2) Fill system using a 50/50 mixture of water and
antifreeze. This is described in the Coolant section of
this group. Fill the radiator to the top and install the
radiator cap. Add sufficient coolant to the reserve/
overflow tank to raise the level to the FULL mark.
(3) Operate the engine with the radiator cap and
reserve/overflow tank cap in place. After the engine
has reached the normal operating temperature, shut
the engine off and allow it to cool.
(4) Add coolant to the reserve/overflow tank as
necessary.Only add coolant when the engine is
cold. Coolant level in a warm engine will be
higher due to thermal expansion.
XJ MODELS
(1) Tighten the radiator draincock and the cylinder
block drain plug(s). If removed, install coolant tem-
perature sensor (4.0L engine).
(2) Fill system using a 50/50 mixture of water and
antifreeze as described in the Coolant section of this
group. Fill radiator to top and install radiator cap.
Add sufficient coolant to reserve/overflow tank to
raise level to FULL mark.
(3) With heater control unit in the HEAT position,
operate engine with radiator cap in place.
(4) After engine has reached normal operating
temperature, shut engine off and allow it to cool.
(5) Add coolant to reserve/overflow tank as neces-
sary.Only add coolant when the engine is cold.
Coolant level in a warm engine will be higher
due to thermal expansion.
COOLING SYSTEM CLEANING/REVERSE FLUSHING
CAUTION: The cooling system normally operates at
97-to-124 kPa (14-to-18 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.
CLEANING
Drain cooling system and refill with water. Run
engine with radiator cap installed until upper radia-
tor hose is hot. Stop engine and drain water from
system. If water is dirty, fill system with water, run
engine and drain system. Repeat until water drains
clean.
REVERSE FLUSHING
Reverse flushing of the cooling system is the forc-
ing of water through the cooling system. This is done
using air pressure in the opposite direction of normal
coolant flow. It is usually only necessary with very
dirty systems with evidence of partial plugging.
REVERSE FLUSHING RADIATOR
Disconnect the radiator hoses from the radiator fit-
tings. Attach a section of radiator hose to the radia-
tor bottom outlet fitting and insert the flushing gun.
Connect a water supply hose and air supply hose to
the flushing gun.
CAUTION: The cooling system normally operates at
97-to-124 kPa (14-to-18 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.
Allow the radiator to fill with water. When radia-
tor is filled, apply air in short blasts allowing radia-
tor to refill between blasts. Continue this reverse
flushing until clean water flows out through rear of
radiator cooling tube passages. For more information,
refer to operating instructions supplied with flushing
equipment. Have radiator cleaned more extensively
by a radiator repair shop.
Fig. 18 Draincock AccessÐXJ Models with 4.0L
Engine
JCOOLING SYSTEM 7 - 17