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 sys-
tem designed for ethylene-glycol. Propylene glycol
also has poorer heat transfer characteristics than
ethylene glycol. This can increase cylinder head tem-
peratures under certain conditions.
Propylene-glycol/ethylene-glycol
Mixtures
can
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.
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 indicated by mixture ratio of coolant to
water.
ENGINE THERMOSTAT—2.0L ENGINE
DESCRIPTION
The 2.0L engine thermostat is located on the front
of the engine (radiator side) in the thermostat hous-
ing/engine outlet connector (Fig. 2). The thermostat
has a air bleed vent located in the flange and a
O-ring with a locating dimple incorporate on it.
There is a relief in the housing for positioning the air
bleed.
OPERATION
The engine cooling thermostat is a wax pellet
driven, reverse poppet choke type. The thermostat 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 auto-
matically 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.
WATER PUMP—2.0L ENGINE
DESCRIPTION
The water pump has a diecast aluminum body and
housing with a stamped steel impeller. The water
pump bolts directly to the block (Fig. 3) and is driven
by the timing belt. Cylinder block to water pump
sealing is provided by a rubber O-ring.
Fig. 2 Thermostat/Engine Outlet Connector—2.0L
Engine
1 – PRESSURE CAP
2 – THERMOSTAT HOUSING/ENGINE OUTLET CONNECTOR
3 – THERMOSTAT
4 – O-RING
5 – VENT FACING UP
Fig. 3 Water Pump
1 – CYLINDER BLOCK
2 – PUMP BODY
JX
COOLING SYSTEM
7 - 3
DESCRIPTION AND OPERATION (Continued)