Pressure Testing Radiator Cap; Radiator Cap-To-Filler Neck Seal - Jeep 1997 Grand Cherokee Service Manual

7 - 20 COOLING SYSTEM
DIAGNOSIS AND TESTING (Continued)
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT 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.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 88° C (190° F).
Fan drive engagement should have started to occur
at between 74° to 82° C (165° to 180° F). Engage-
ment is distinguishable by a definite increase in fan
flow noise (roaring). The timing light also will indi-
cate an increase in the speed of the fan.
(7) When the air temperature reaches 88° C (190°
F), remove the plastic sheet. Fan drive disengage-
ment should have started to occur at between 57° to
79° C (135° to 175° F). A definite decrease of fan
flow noise (roaring) should be noticed. If not, replace
the defective viscous fan drive unit.

RADIATOR CAP-TO-FILLER NECK SEAL—

PRESSURE 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
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 cap
except for the following purposes:
• To check and adjust antifreeze freeze point.
• To refill system with new antifreeze.
• For conducting service procedures.
• When checking for vacuum leaks.
WARNING: IF VEHICLE
RECENTLY, WAIT AT LEAST 15 MINUTES BEFORE
REMOVING RADIATOR
SQUEEZE RADIATOR UPPER HOSE TO CHECK IF
SYSTEM IS UNDER PRESSURE. PLACE A RAG
OVER THE CAP AND WITHOUT PUSHING DOWN,
ROTATE CAP COUNTER-CLOCKWISE
FIRST STOP. ALLOW FLUID TO ESCAPE THROUGH
OVERFLOW HOSE
OVERFLOW TANK. SQUEEZE RADIATOR UPPER
HAS BEEN
CAP. WITH A
TO
INTO COOLANT RESERVE/
TYPICAL COOLING SYSTEM PRESSURE TESTER
HOSE TO DETERMINE WHEN PRESSURE HAS
BEEN RELEASED. WHEN COOLANT AND STEAM
STOP BEING PUSHED INTO TANK AND SYSTEM
PRESSURE
COMPLETELY.

PRESSURE TESTING RADIATOR CAP

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. 20).
Fig. 20 Pressure Testing Radiator PressureCap—
Operate the tester pump and observe the gauge
pointer at its highest point. The cap release pressure
should be 97 to 124 kPa (14 to 18 psi). The cap is
satisfactory when the pressure holds steady. It is also
good if it holds pressure within the 97 to 124 kPa (14
to 18 psi) range for 30 seconds or more. If the pointer
drops quickly, replace the cap.
CAUTION: Radiator pressure testing tools are very
sensitive to small air leaks, which will not cause
cooling system problems. A pressure cap that does
RUN
not have a history of coolant loss should not be
replaced just because it leaks slowly when tested
RAG,
with this tool. Add water to tool. Turn tool upside
down and recheck pressure cap to confirm that cap
needs replacement.
THE
DROPS, REMOVE RADIATOR
Typical
PRESSURE CAP
ZG
CAP