Jeep Wrangler TJ. Manual - part 270
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - RADIATOR
CAP-TO-FILLER NECK SEAL
The pressure cap upper gasket (seal) pressure
relief can be tested by removing overflow hose from
radiator filler neck nipple. Attach hose of pressure
tester tool 7700 (or equivalent) to nipple. It will be
necessary to disconnect hose from its adapter for
filler neck. Pump air into radiator. The pressure cap
upper gasket should relieve at 69-124 kPa (10-18 psi)
and hold pressure at a minimum of 55 kPa (8 psi).
WARNING: THE WARNING WORDS - DO NOT OPEN
HOT - ON RADIATOR PRESSURE CAP, ARE A
SAFETY PRECAUTION. WHEN HOT, PRESSURE
BUILDS UP IN COOLING SYSTEM. TO PREVENT
SCALDING OR INJURY, RADIATOR CAP SHOULD
NOT BE REMOVED WHILE SYSTEM IS HOT AND/OR
UNDER PRESSURE.
Do not remove radiator cap at any time except for
the following purposes:
(1) Check and adjust antifreeze freeze point.
(2) Refill system with new antifreeze.
(3) Conducting service procedures.
(4) Checking for vacuum leaks.
WARNING: IF VEHICLE HAS BEEN RUN RECENTLY,
WAIT AT LEAST 15 MINUTES BEFORE REMOVING
RADIATOR CAP. WITH A RAG, SQUEEZE RADIATOR
UPPER HOSE TO CHECK IF SYSTEM IS UNDER
PRESSURE. PLACE A RAG OVER CAP AND WITH-
OUT PUSHING CAP DOWN, ROTATE IT COUNTER-
CLOCKWISE TO FIRST STOP. ALLOW FLUID TO
ESCAPE
THROUGH
THE
COOLANT
RESERVE/
OVERFLOW
HOSE
INTO
RESERVE/OVERFLOW
TANK. SQUEEZE RADIATOR UPPER HOSE TO
DETERMINE
WHEN
PRESSURE
HAS
BEEN
RELEASED. WHEN COOLANT AND STEAM STOP
BEING PUSHED INTO TANK AND SYSTEM PRES-
SURE DROPS, REMOVE RADIATOR CAP COM-
PLETELY.
DIAGNOSIS AND TESTING - RADIATOR CAP
Remove cap from radiator. Be sure that sealing
surfaces are clean. Moisten rubber gasket with water
and install cap on pressure tester 7700 or an equiv-
alent (Fig. 35).
Operate tester pump to bring pressure to 117 kPa
(17 psi) on gauge. If pressure cap fails to hold pres-
sure of at least 110 kPa (16 psi) replace cap. Refer to
the following CAUTION.
The pressure cap may test properly while posi-
tioned on tool 7700 (or equivalent). It may not hold
pressure or vacuum when installed on radiator. If so,
inspect radiator filler neck and cap’s top gasket for
damage. Also inspect for dirt or distortion that may
prevent cap from sealing properly.
CAUTION: Radiator pressure testing tools are very
sensitive to small air leaks, which will not cause
cooling system problems. A pressure cap that does
not have a history of coolant loss should not be
replaced just because it leaks slowly when tested
with this tool. Add water to tool. Turn tool upside
down and recheck pressure cap to confirm that cap
needs replacement.
CLEANING
Use only a mild soap and water to clean the radi-
ator cap. Using any type solvent may cause damage
to the seal in the radiator cap.
INSPECTION
Hold cap at eye level, right side up. The vent valve
(Fig. 34) at bottom of cap should open. If rubber gas-
ket has swollen and prevents vent valve from open-
ing, replace cap.
Hold cap at eye level, upside down. If any light can
be seen between vent valve and rubber gasket,
replace cap. Do not use a replacement cap that
has a spring to hold vent shut. A replacement cap
must be the type designed for a coolant reserve/over-
flow system with a completely sealed diaphragm
Fig. 35 Pressure Testing Radiator Cap - Typical
1 - PRESSURE CAP
2 - TYPICAL COOLING SYSTEM PRESSURE TESTER
TJ
ENGINE
7 - 41
RADIATOR PRESSURE CAP (Continued)