Coolant; Low Coolant Level Sensor; Description And Operation; Coolant Performance - Jeep 1997 Grand Cherokee Service Manual

7 - 4 COOLING SYSTEM
GENERAL INFORMATION (Continued)
A quick test to determine if the pump is working is
to check if the heater warms properly. A defective
water pump will not be able to circulate heated cool-
ant through the long heater hose to the heater core.

COOLANT

The cooling system is designed around the coolant.
Coolant flows through the engine water jackets and
water manifold absorbing heat produced during
engine operation. The coolant carries heat to the
radiator and heater core. Here it is transferred to the
ambient air passing through the radiator and heater
core fins.

LOW COOLANT LEVEL SENSOR

The low coolant level sensor checks for low coolant
level in the coolant tank. A signal will be sent from
this sensor to the powertrain control module (PCM).
When the PCM determines low coolant level, the
instrument panel mounted low coolant level warning
lamp will be illuminated. The sensor is located on the
bottom of the coolant tank. For information, refer to
Group 8E, Instrument Panel and Gauges.
If this lamp is illuminated, it indicates the need for
service.

DESCRIPTION AND OPERATION

THERMOSTAT
A pellet-type thermostat controls the operating
temperature of the engine by controlling the amount
of coolant flow to the radiator. The thermostat starts
to open at 80°C (176°F). Above this temperature,
coolant is allowed to flow to the radiator. This pro-
vides quick engine warmup and overall temperature
control.
The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance,
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
CAUTION: Do not operate an engine without a
thermostat, except for servicing or testing.
PRESSURE/VENT CAP
The pressure/vent cap is cam type cap. This cap
releases excess pressure at some point within a
range of 90 - 117 kPa (13 - 17 psi). The actual pres-
sure relief point (in pounds) is labeled on top of the
cap.
increased exhaust
The cooling system will operate at pressures
slightly above atmospheric pressure. This results in a
higher coolant boiling point allowing increased radi-
ator cooling capacity. The cap contains a spring-
loaded pressure relief valve. This valve opens when
system pressure reaches approximately 103 kPa (15
psi).
When the engine is cooling down, vacuum is
formed within the cooling system. To prevent collapse
of the radiator and coolant hoses from this vacuum, a
vacuum valve is used within the cap. This valve pre-
vents excessive pressure differences from occurring
between the closed cooling system and the atmo-
sphere. If the vacuum valve is stuck shut, the radia-
tor and/or cooling system hoses will collapse on cool-
down.
NOTE: Do not use any type of tool when tighten-
ing the cap. Hand tighten only (approximately 5 N·m
or 44 in. lbs.) torque.

COOLANT PERFORMANCE

ETHYLENE-GLYCOL MIXTURES
The required ethylene-glycol (antifreeze) and water
mixture depends upon the climate and vehicle oper-
ating conditions. The recommended mixture of 50/50
ethylene-glycol and water will provide protection
against freezing to -37 deg. C (-35 deg. F). The anti-
freeze concentration must always be a minimum of
44 percent, year-round in all climates. If percentage
is lower than 44 percent, engine parts may be
eroded by cavitation, and cooling system com-
ponents may be severely damaged by corrosion.
Maximum protection against freezing is provided
with a 68 percent antifreeze concentration, which
prevents freezing down to -67.7 deg. C (-90 deg. F). A
higher percentage will freeze at a warmer tempera-
ture. Also, a higher percentage of antifreeze can
cause the engine to overheat because the specific
heat of antifreeze is lower than that of water.
100 Percent Ethylene-Glycol—Should Not Be Used in
Chrysler Vehicles
Use of 100 percent ethylene-glycol will cause for-
mation of additive deposits in the system, as the cor-
rosion inhibitive additives in ethylene-glycol require
the presence of water to dissolve. The deposits act as
insulation, causing temperatures to rise to as high as
149 deg. C (300) deg. F). This temperature is hot
enough to melt plastic and soften solder. The
increased temperature can result in engine detona-
tion. In addition, 100 percent ethylene-glycol freezes
at 22 deg. C (-8 deg. F ).
ZG