See Coolant Level Check Service and Deaeration,
and Pressure Cap sections for operation and service.
Vehicles equipped with the electric monitor system
have a level sensor in the CRS tank, see Group 8,
Electrical, for service.
RADIATOR PRESSURE CAP
Radiators are equipped with a pressure cap that
releases pressure at some point within a range of
97-124 kPa (14-18 psi).
The system will operate at higher than atmospheric
pressure that raises the coolant boiling point allowing
increased radiator cooling capacity.
There is also a vent valve in the center of the cap.
This valve also opens when coolant is cooling and
contracting allowing coolant to return to radiator from
coolant reserve system tank by vacuum through con-
necting hose. If valve is stuck shut, the radiator
hoses will be collapsed on cool down. Clean the
vent valve (Fig. 16) to ensure proper sealing
when boiling point is reached.
The gasket in the cap seals the filler neck, so that
vacuum can be maintained, allowing coolant to be
drawn back into the radiator from the reserve tank.
RADIATOR CAP TO FILLER NECK SEAL PRES-
SURE RELIEF CHECK
The pressure cap upper gasket (seal) pressure relief
can be checked by removing the overflow hose at the
radiator filler neck nipple (Fig. 16). Attach the Radia-
tor Pressure Tool to the filler neck nipple and pump air
into the radiator. Pressure cap upper gasket should
relieve at 69-124 kPa (10-18 psi) and hold pressure at
55 kPa (8 psi) minimum.
WARNING: THE WARNING WORDS DO NOT OPEN
HOT ON THE RADIATOR PRESSURE CAP IS A
SAFETY PRECAUTION. WHEN HOT, PRESSURE
BUILDS UP IN COOLING SYSTEM. TO PREVENT
SCALDING
OR
INJURY,
THE
RADIATOR
CAP
SHOULD NOT BE REMOVED WHILE THE SYSTEM IS
HOT OR UNDER PRESSURE.
There is no need to remove the radiator cap at any
time except for the following purposes:
(1) Check and adjust antifreeze freeze point.
(2) Refill system with new anti-freeze.
(3) Conducting service procedures.
(4) Checking for vacuum leaks.
WARNING: IF VEHICLE HAS BEEN RUN RECENTLY,
WAIT 15 MINUTES BEFORE REMOVING CAP. THEN
PLACE A SHOP TOWEL OVER THE CAP AND WITH-
OUT
PUSHING
DOWN
ROTATE
COUNTER-
CLOCKWISE TO THE FIRST STOP. ALLOW FLUIDS
TO ESCAPE THROUGH THE OVERFLOW TUBE AND
WHEN THE SYSTEM STOPS PUSHING COOLANT
AND STEAM INTO THE CRS TANK AND PRESSURE
DROPS PUSH DOWN AND REMOVE THE CAP COM-
PLETELY. SQUEEZING THE RADIATOR INLET HOSE
WITH A SHOP TOWEL (TO CHECK PRESSURE) BE-
FORE AND AFTER TURNING TO THE FIRST STOP IS
RECOMMENDED.
PRESSURE TESTING RADIATOR CAP
Dip the pressure cap in water, clean any deposits off
the vent valve or its seat and apply cap to end of
Radiator Pressure Tool. Working the plunger, bring the
pressure to 104 kPa (15 psi) on the gauge. If the
pressure cap fails to hold pressure of at least 97 kPa
(14 psi) replace cap. See CAUTION.
If the pressure cap tests properly while positioned on
Radiator Pressure Tool (Fig. 17), but will not hold
pressure or vacuum when positioned on the radiator.
Inspect the radiator filler neck and cap top gasket for
irregularities that may prevent the cap from sealing
properly.
CAUTION: Radiator Pressure Tool is very sensitive to
small air leaks that 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 the tool. Turn tool upside down and
recheck pressure cap to confirm that cap is bad.
INSPECTION
Hold the cap in hand, right side up (Fig. 16). The
vent valve at the bottom of the cap should open. If the
rubber gasket has swollen and prevents the valve from
opening, replace the cap.
Hold the cleaned cap in hand upside down. If any
light shows between vent valve and rubber gasket,
replace cap. Do not use a replacement cap that has
a spring to hold the vent shut.
Replacement cap must be of the type designed for
coolant reserve system with a completely sealed dia-
phragm spring, and rubber gasket to seal to filler neck
top surface. This design assures coolant return to
radiator.
Fig. 16 Radiator Pressure Cap Filler Neck
.
COOLING SYSTEM
7 - 17