Coolant Selection-Additives - Jeep 1997 Grand Cherokee Service Manual

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DESCRIPTION AND OPERATION (Continued)
The more common type of thermostat failure, usu-
ally found on high mileage vehicles, is a thermostat
failed in the shut position. The temperature gauge (if
equipped) will give an indication of this condition.
Depending upon length of time that vehicle is oper-
ated, pressure cap may vent. This will expel steam
and coolant to coolant reserve/overflow tank and to
surface below vehicle. Refer to the Diagnosis section
of this group.
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 ).
Propylene-glycol Formulations—Should Not Be Used in
Chrysler Vehicles
Propylene-glycol formulations do not meet
Chrysler coolant specifications. It's overall effec-
tive temperature range is smaller than that of ethyl-
ene-glycol. The freeze point of 50/50 propylene-glycol
and water is -32 deg. C (-26 deg. F). 5 deg. C higher
than ethylene-glycol's freeze point. The boiling point
(protection against summer boil-over) of propylene-
glycol is 125 deg. C (257 deg. F ) at 96.5 kPa (14 psi),
compared to 128 deg. C (263 deg. F) for ethylene-gly-
col. Use of propylene-glycol can result in boil-over or
freeze-up in Chrysler vehicles, which are designed for
ethylene-glycol. Propylene glycol also has poorer heat
transfer characteristics than ethylene glycol. This
can increase cylinder head temperatures under cer-
tain conditions.
Propylene-glycol/Ethylene-glycol Mixtures—Should Not Be
Used in Chrysler Vehicles
Propylene-glycol/ethylene-glycol
cause the destabilization of various corrosion inhibi-
tors, causing damage to the various cooling system
components. Also, once ethylene-glycol and propy-
lene-glycol based coolants are mixed in the vehicle,
conventional methods of determining freeze point will
not be accurate. Both the refractive index and spe-
cific gravity differ between ethylene glycol and propy-
lene glycol.
CAUTION: Richer antifreeze mixtures cannot be
measured with normal field equipment and can
cause problems associated with 100 percent ethyl-
ene-glycol.

COOLANT SELECTION-ADDITIVES

The presence of aluminum components in the cool-
ing system requires strict corrosion protection. Main-
tain coolant at specified level with a mixture of
ethylene-glycol based antifreeze and water. Chrysler
Corporation recommends Mopar Antifreeze or equiv-
alent. If coolant becomes contaminated or looses
color, drain and flush cooling system and fill with
correctly mixed solution.
A 0.25 percent emulsifiable oil is added to the radi-
ator at the factory to prevent solder corrosion.
CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
RADIATOR PRESSURE CAP
All radiators are equipped with a pressure cap.
This cap releases pressure at some point within a
range of 97-to-124 kPa (14-to-18 psi). The pressure
relief point (in pounds) is engraved on top of the cap
(Fig. 7).
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 (Fig. 7) contains a
spring-loaded pressure relief valve. This valve opens
when system pressure reaches the release range of
97-to-124 kPa (14-to-18 psi).
A vent valve in the center of the cap allows a small
coolant flow through the cap when coolant is below
boiling temperature. The valve is completely closed
when boiling point is reached. As the coolant cools, it
contracts and creates a vacuum in cooling system.
COOLING SYSTEM
Mixtures
7 - 5
can