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7 - 16
COOLING SYSTEM
•
RADIATOR PRESSURE CAP
Radiators are equipped w i t h a pressure cap w h i c h
releases pressure a t some p o i n t w i t h i n a range o f 97-
124 k P a (14-18 psi). T h e pressure r e l i e f point ( i n
pounds) i s engraved o n top o f t h e cap.
The
cooling
system
w i l l
operate
a t pressures
s l i g h t l y above atmospheric pressure. T h i s results i n a
higher coolant b o i l i n g p o i n t a l l o w i n g increased r a d i -
ator cooling capacity. T h e cap ( F i g . 9) contains a
spring-loaded pressure r e l i e f valve t h a t opens w h e n
system pressure reaches t h e release range o f 97-124
kPa (14-18 psi).
Fig. 9 Radiator Pressure Cap and Filler Neck
A vent valve i n the center of the cap allows a s m a l l
coolant flow t h r o u g h t h e cap w h e n coolant is below
b o i l i n g temperature. T h e valve is completely closed
w h e n b o i l i n g p o i n t is reached. A s coolant cools i t con-
tracts a n d creates a v a c u u m i n t h e cooling system.
This causes t h e v a c u u m valve t o open and coolant i n
reserve bottle t o be d r a w n t h r o u g h connecting hose
into r a d i a t o r . I f the v a c u u m valve is stuck shut r a d i -
ator hoses w i l l collapse on cool down. Clean t h e vent
valve ( F i g . 11) t o ensure proper sealing.
A rubber gasket seals t h e r a d i a t o r filler neck to
prevent leakage w h e n system is under pressure and
to m a i n t a i n v a c u u m d u r i n g coolant cool down allow-
i n g coolant t o r e t u r n f r o m t h e reserve t a n k .
RADIATOR
CAP TO FILLER
NECK
SEAL,
PRESSURE
RELIEF
CHECK
The pressure cap upper gasket (seal) pressure r e l i e f
can be tested b y r e m o v i n g the overflow hose from t h e
radiator filler neck nipple a n d a t t a c h i n g t h e hose o f
pressure tester tool 7700-A t o t h e nipple. I t w i l l be
necessary t o disconnect t h e hose f r o m it's adapter for
the filler neck. Pump a i r i n t o t h e radiator. The pres-
sure cap upper gasket should relieve at 69- 124 k P a
(10-18 psi) a n d hold pressure a t a m i n i m u m of 55
kPa (8 psi).
WARNING: THE WARNING WORDS " D O NOT OPEN
HOT" O N T H E RADIATOR PRESSURE C A P ARE A
SAFETY
PRECAUTION.
WHEN
HOT, PRESSURE
BUILDS UP IN COOLING
SYSTEM. T O PREVENT
SCALDING
OR INJURY,
T H E RADIATOR
C A P
SHOULD NOT B E REMOVED WHILE THE SYSTEM
IS HOT AND/OR UNDER PRESSURE.
There i s no need t o remove t h e r a d i a t o r cap a t a n y
t i m e e x c e p t
for t h e f o l l o w i n g purposes:
(1) Check a n d adjust anti-freeze freeze point.
(2) R e f i l l system w i t h n e w anti-freeze.
(3) C o n d u c t i n g service procedures.
(4) C h e c k i n g for v a c u u m leaks.
WARNING: IF VEHICLE H A S BEEN RUN RECENTLY,
WAIT A T LEAST 15 MINUTES BEFORE
REMOVING
RADIATOR
CAP. WITH A RAG, SQUEEZE
RADIA-
TOR UPPER HOSE T O CHECK IF SYSTEM IS U N -
DER PRESSURE. PLACE A RAG OVER T H E C A P
AND WITHOUT PUSHING C A P DOWN ROTATE IT
COUNTER-CLOCKWISE
T O THE FIRST STOP. A L -
LOW
FLUID T O ESCAPE THROUGH
OVERFLOW
HOSE
INTO
COOLANT
RESERVE
BOTTLE.
SQUEEZE
RADIATOR
UPPER HOSE T O DETER-
MINE WHEN
PRESSURE H A S BEEN
RELEASED.
WHEN
COOLANT
A N D STEAM
STOP
BEING
PUSHED INTO BOTTLE A N D SYSTEM PRESSURE
DROPS REMOVE RADIATOR C A P COMPLETELY.
PRESSURE TESTING RADIATOR CAPS
Remove cap f r o m r a d i a t o r . Ensure t h a t sealing sur-
faces are clean. M o i s t e n r u b b e r gasket w i t h w a t e r
and i n s t a l l t h e cap on pressure tester 7700-A o r a n
equivalent (Fig. 10).
Fig. 10 Pressure Testing Radiator Cap
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