Jeep Wrangler TJ. Manual - part 262

DIAGNOSIS AND TESTING - COOLING SYSTEM
- TESTING FOR LEAKS

ULTRAVIOLET LIGHT METHOD

All Jeep 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
parts 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 commercially available black light tool 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.
4).

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. Replace cap if
cams are bent.

Attach pressure tester 7700 (or an equivalent) to

the radiator filler neck (Fig. 5).

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:

• Holds 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
Leakage Test. Do this if it is certain that coolant is
being lost and no leaks can be detected.

• Drops Slowly: Shows a small leak or seepage is

occurring. 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.

• Drops Quickly: Shows that a serious leakage is

occurring. Examine the system for serious external
leakage. If no leaks are visible, inspect for internal

Fig. 4 Leak Detection Using Black Light—Typical

1 - TYPICAL BLACK LIGHT TOOL

Fig. 5 Pressurizing System - Typical

1 - TYPICAL COOLING SYSTEM PRESSURE TESTER

COOLING

7 - 9

COOLING (Continued)

leakage. Large radiator leak holes should be repaired
by a reputable radiator repair shop.

INTERNAL LEAKAGE INSPECTION

Remove the engine oil pan drain plug and drain a

small amount of engine oil. Coolant, being heavier
than engine oil, will drain first. Another way of test-
ing is to operate the engine and check for water glob-
ules on the engine oil dipstick. Also inspect the
automatic transmission oil dipstick for water glob-
ules. Inspect the automatic transmission fluid cooler
for leakage. Operate the engine 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 a result of a
faulty cylinder head gasket or crack in the engine.
Repair as necessary.

WARNING:

NOT

ALLOW

PRESSURE

EXCEED 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:

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.

Remove thermostat (Refer to 7 - COOLING/EN-

GINE/ENGINE

COOLANT

THERMOSTAT

REMOVAL).

Remove accessory drive belt (Refer to 7 - COOL-

ING/ACCESSORY

DRIVE/DRIVE

BELTS

REMOVAL).

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
internal combustion gas leakage.

DIAGNOSIS AND TESTING - 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.

STANDARD PROCEDURE

STANDARD PROCEDURE - DRAINING COOLING
SYSTEM - 2.4L

WARNING:

NOT

REMOVE

THE

CYLINDER

BLOCK DRAIN PLUGS (Fig. 6) OR LOOSEN THE
RADIATOR DRAINCOCK WITH SYSTEM HOT AND
UNDER

PRESSURE.

SERIOUS

BURNS

FROM

COOLANT CAN OCCUR.

(1) DO NOT remove radiator cap first. With engine

cold, raise vehicle on a hoist and locate radiator
draincock.

NOTE: Radiator draincock is located on the left/
lower side of radiator facing to rear of vehicle.

(2) Attach one end of a hose to the draincock. Put

the other end into a clean container. Open draincock
and drain coolant from radiator. This will empty the
coolant reserve/overflow tank. The coolant does not
have to be removed from the tank unless the system
is being refilled with a fresh mixture. When tank is

7 - 10

COOLING

COOLING (Continued)

empty, remove radiator cap and continue draining
cooling system.

STANDARD PROCEDURE - REFILLING
COOLING SYSTEM - 2.4L

(1) Tighten the radiator draincock and the cylinder

block drain plug(s) (if removed).

CAUTION: Failure to purge air from the cooling sys-
tem can result in an overheating condition and
severe engine damage.

(2) Fill system using a 50/50 mixture of ethylene-

glycol antifreeze and low mineral content water. Fill
pressure bottle to service line and install cap.

NOTE: The engine cooling system will push any
remaining air into the coolant bottle within about an
hour of normal driving. As a result, a drop in cool-
ant level in the pressure bottle may occur. If the
engine cooling system overheats and pushes cool-
ant into the overflow side of the coolant bottle, this
coolant will be sucked back into the cooling system
ONLY IF THE PRESSURE CAP IS LEFT ON THE
BOTTLE. Removing the pressure cap breaks the
vacuum path between the two bottle sections and
the coolant will not return to cooling system.

(3) With heater control unit in the HEAT position,

operate engine with pressure bottle cap in place.

(4) Add coolant to pressure bottle as necessary.

Only add coolant to the pressure bottle when

the engine is cold. Coolant level in a warm
engine will be higher due to thermal expansion.

NOTE: The coolant bottle has two chambers. Cool-
ant will normally only be in the outboard (larger) of
the two. The inboard chamber is only to recover
coolant in the event of an overheat or after a recent
service fill. The inboard chamber should normally
be empty. If there is coolant in the overflow side of
the coolant bottle (after several warm/cold cycles of
the engine) and coolant level is above cold full
when cold, disconnect the end of the overflow hose
at the fill neck and lower it into a clean container.
Allow coolant to drain into the container until emp-
tied. Reconnect overflow hose to fill neck.

STANDARD PROCEDURE - COOLANT LEVEL
CHECK

NOTE: Do not remove radiator cap for routine cool-
ant 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.

STANDARD PROCEDURE - COOLING SYSTEM -
DRAINING

WARNING:

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,
remove 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 block by removing

drain plug at left rear side of block (Fig. 7).

Fig. 6 Drain Plug - 3.7L Engine

1 - CYLINDER BLOCK DRAIN PLUG
2 - EXHAUST MANIFOLD AND HEAT SHIELD

COOLING

7 - 11

COOLING (Continued)

STANDARD PROCEDURE - COOLING SYSTEM -
REFILLING

(1) Tighten the radiator draincock and the cylinder

block drain plug(s).

(2) Fill system using a 50/50 mixture of water and

antifreeze. 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 both the radiator cap

and reserve/overflow tank cap in place. After the
engine has reached the normal operating tempera-
ture, 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.

STANDARD PROCEDURE - COOLING SYSTEM -
REVERSE FLUSHING

CAUTION: The cooling system normally operates at
97 - 110 C.P.A. 14 - 16 -16 psi) pressure. Exceeding
this pressure may damage the radiator or hoses.

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.

CHEMICAL CLEANING

If visual inspection indicates the formation of

sludge or scaly deposits, use a radiator cleaner

(Mopar Radiator Kleen or equivalent) before flushing.
This will soften scale and other deposits and aid the
flushing operation.

CAUTION: Be sure instructions on the container are
followed.

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 - 110 C.P.A. (14 - 16 psi) pressure. Exceeding this
pressure may damage the radiator or hoses.

Allow the radiator to fill with water. When radiator

is filled, apply air in short blasts allowing radiator 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 equip-
ment. Have radiator cleaned more extensively by a
radiator repair shop.

REVERSE FLUSHING ENGINE

Drain the cooling system (Refer to 7 - COOLING -

STANDARD PROCEDURE). Remove the thermostat
housing and thermostat. Install the thermostat hous-
ing. Disconnect the radiator upper hose from the
radiator and attach the flushing gun to the hose. Dis-
connect the radiator lower hose from the water
pump. Attach a lead away hose to the water pump
inlet fitting.

CAUTION: 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 water.
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 sup-
plied with flushing equipment.

Remove the lead away hose, flushing gun, water

supply hose and air supply hose. Remove the thermo-
stat housing (Refer to 7 - COOLING/ENGINE/EN-
GINE

COOLANT

THERMOSTAT

REMOVAL).

Install the thermostat and housing with a replace-
ment gasket (Refer to 7 - COOLING/ENGINE/EN-
GINE

COOLANT

THERMOSTAT

Fig. 7 Draining Coolant From Block - 2.4L/4.0L Engines

1 - EXHAUST MANIFOLD
2 - CYLINDER BLOCK COOLANT DRAIN PLUG

7 - 12

COOLING

COOLING (Continued)

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