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 MIXTURES
It’s overall effective temperature range is smaller than
that of ethylene-glycol. The freeze point of 50/50 propy-
lene-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-glycol.
Use of propylene-glycol can result in boil-over or
freeze-up on a cooling system designed for ethylene-gly-
col. Propylene glycol also has poorer heat transfer char-
acteristics than ethylene glycol. This can increase
cylinder head temperatures under certain conditions.
Propylene-glycol/ethylene-glycol Mixtures can cause
the destabilization of various corrosion inhibitors,
causing damage to the various cooling system compo-
nents. Also, once ethylene-glycol and propylene-glycol
based coolants are mixed in the vehicle, conventional
methods of determining freeze point will not be accu-
rate. Both the refractive index and specific gravity dif-
fer between ethylene glycol and propylene glycol.
OPERATION
ETHYLENE-GLYCOL MIXTURES
Coolant flows through the engine block absorbing the
heat from the engine, then flows to the radiator where
the cooling fins in the radiator transfers the heat from
the coolant to the atmosphere. During cold weather the
ethylene-glycol coolant prevents water present in the
cooling system from freezing within temperatures indi-
cated by mixture ratio of coolant to water.
ENGINE THERMOSTAT—2.5L ENGINE
DESCRIPTION
The 2.5L engine thermostat is located in a thermo-
stat housing, located below the throttle body. This
thermostat has an air bleed valve, located in the
thermostat flange (Fig. 2).
OPERATION
The engine cooling thermostat is a wax pellet
driven, reverse poppet choke type. It is designed to
provide the fastest warm up possible by preventing
leakage through it and to guarantee a minimum
engine operating temperature of 88 to 93°C (192 to
199°F). The thermostat also will automatically reach
wide open so it will not restrict flow to the radiator
as temperature of the coolant rises in hot weather to
around 104°C (220°F). Above this temperature the
coolant temperature is controlled by the radiator, fan,
and ambient temperature, not the thermostat.
The thermostat is operated by a wax filled con-
tainer (pellet) which is sealed. When heated coolant
reaches
a
predetermined
temperature,
the
wax
expands enough to overcome the closing spring and
water pump pressure, which forces the valve to open.
Coolant leakage into the wax pellet will cause a
thermostat to fail open. Do not attempt to free-up a
stuck open thermostat.
COOLANT RECOVERY SYSTEM
DESCRIPTION
The coolant recovery system consist of a container
and hose that is connected to the cooling system.
Fig. 2 Thermostat, Housing and Inlet Elbow—2.5L
Engine
1 – THERMOSTAT HOUSING
2 – VENT INSTALLED UPWARD
3 – THERMOSTAT
4 – COOLANT INLET ELBOW
JX
COOLING SYSTEM
7 - 3
DESCRIPTION AND OPERATION (Continued)