OPERATION
A vent valve in the center of the cap will remain
shut as long as the cooling system is pressurized. As
the coolant cools, it contracts and creates a vacuum
in cooling system. This causes the vacuum valve to
open and coolant in reserve/overflow tank to be
drawn through connecting hose into radiator. If the
vacuum valve is stuck shut, or overflow hose is
kinked, radiator hoses will collapse on cool-down.
DIAGNOSIS AND TESTING - RADIATOR
PRESSURE 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. 14).
Operate the tester pump and observe the gauge
pointer at its highest point. The cap release pressure
should be 124 to 145 kPa (18 to 21 psi). The cap is
satisfactory when the pressure holds steady. It is also
good if it holds pressure within the 124 to 145 kPa
(18 to 21 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
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
Clean the radiator pressure cap using a mild soap
and water only.
INSPECTION
Visually inspect the pressure valve gasket on the
cap. Replace cap if the gasket is swollen, torn or
worn. Inspect the area around radiator filler neck for
white deposits that indicate a leaking cap.
RADIATOR
DESCRIPTION
The radiator used with the 2.7L diesel is con-
structed of a horizontal down-flow aluminum core
with plastic side tanks.
CAUTION: Plastic tanks, while stronger than brass,
are subject to damage by impact, such as
wrenches.
COOLING MODULE
The cooling module assembly includes the radia-
torand hydraulic fan assembly. To replace either one
of these components, the entire assembly must be
removed from the vehicle and then disassembled.
(Refer to 7 - COOLING/ENGINE/RADIATOR -
REMOVAL)
DIAGNOSIS AND TESTING - RADIATOR FLOW
TEST
There is coolant flow through the coolant recovery
container before and after the thermostat opens. If
engine is cold, idle engine until normal operating
temperature is reached. Then feel the upper radiator
hose. If the hose is hot, the thermostat is open and
water is circulating through the cooling system.
CAUTION: Do not remove the vent valve to insert a
temperature gauge thought the opening , coolant
will spill out of the system and the engine will not
be filled with coolant up to the heads. Major dam-
age could happen if you run the engine in this con-
dition.
Fig. 14 Pressure Testing Radiator Pressure
Cap—Typical
1 - PRESSURE CAP
2 - TYPICAL COOLING SYSTEM PRESSURE TESTER
7a - 20 ENGINE WG
RADIATOR PRESSURE CAP (Continued)
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