Testing Cooling System For Leaks - Jeep 1997 Grand Cherokee Service Manual

7 - 14 COOLING SYSTEM
DIAGNOSIS AND TESTING (Continued)
CAUTION: Major damage could happen if you run
the engine in this condition.

TESTING COOLING SYSTEM 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 radiator
pressure tester to determine if any external leaks
exist (Fig. 9).
Fig. 9 Leak Detection Using Black Light—Typical
PRESSURE TESTER METHOD
WARNING: HOT, PRESSURIZED COOLANT CAN
CAUSE INJURY BY SCALDING. NEVER REMOVE
THE PRESSURE/VENT CAP OR PRESSURE TESTER
WHEN THE COOLING SYSTEM IS HOT OR UNDER
PRESSURE!
Allow the engine to cool sufficiently so that the
system is not under pressure and carefully remove
the pressure/vent cap from the filler neck. Warm the
engine with the pressure/vent cap off to normal oper-
ating temperature. With the engine turned off attach
the cooling system pressure tester and test the sys-
tem as described below.
Recheck the system cold if the cause of coolant loss
is not located during warm engine examination.
Fig. 10 Typical Cooling System Pressure Tester
Operate the tester pump to apply 103 kPa (15 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
leakage. Large radiator leak holes should be repaired
by a reputable radiator repair shop.
ZG