cooling system LEXUS SC300 1991 Service Manual PDF

Electronic Control Parts
(System Circuit)
(Cooling Fan ECU)
COMPONENTS FOR REMOVAL AND
INSTALLATION
CO±60±
COOLIING SYSTEM Electronically Controlled Hydraulic Cooling Fan
(Electronic Control Parts)
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INSPECTION OF COOLING FAN ECU
1. DISCONNECT CABLE FROM NEGATIVE TERMINAL OFBATTERY
CAUTION: Work must be started after 20 seconds or longer
from the time the ignition switch is turned to the ºLOCKº posi-
tion and the negative (±) terminal cable is disconnected from
the battery.
2. DISCONNECT COOLING FAN ECU CONNECTOR (See Components on page CO±60)
(a) Remove the instrument panel under cover.
(b) Remove the lower instrument panel finish panel and glove compartment door assembly.
(c) Disconnect the cooling fan ECU connector.
3. INSPECT COOLING FAN ECU (a) Connect the cable to the negative (±) terminal of thebattery.
(b) Check the connector on the wiring harness side as shown in the chart.
Check forTester connectionConditionSpecified value
Voltage1±GroundIgnition switch ONBattery voltage
Resistance2±3Solenoid valve at cold (20 5C (68 5F))7.5±8.5

Continuity4±Ground±Continuity
Continuity5±GroundThrottle valve openNo continuityContinuity5±GroundThrottle valve closedContinuity
Resistance9±10Coolant temp. at 80 5C (176 5F)1.48±1.58 k

(c) Disconnect the cable from the negative (±) terminal of
the battery.
4. RECONNECT COOLING FAN ECU CONNECTOR
5. RECONNECT CABLE TO NEGATIVE TERMINAL OF BATTERY
±
COOLIING SYSTEM Electronically Controlled Hydraulic
Cooling Fan (Electronic Control Parts)CO±61
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(Water Temperature Sensor)
COMPONENTS FOR REMOVAL AND
INSTALLATION
INSPECTION OF WATER TEMPERATURE
SENSOR
1. DISCONNECT CABLE FROM NEGATIVE TERMINAL OFBATTERY
CAUTION: Work must be started after 20 seconds or
longer from the time the ignition switch is turned to the
ºLOCKº position and the negative (±) terminal cable is
disconnected from the battery.
2. REMOVE ENGINE UNDER COVER
3. DRAIN ENGINE COOLANT (See page CO±6)
4. REMOVE WATER TEMPERATURE SENSOR (a) Disconnect the water temperature sensor connector.
(b) Remove the water temperature sensor from left side ofthe radiator lower tank.
(c) Remove the O±ring from the water temperature sensor.
CO±62
±
COOLIING SYSTEM Electronically Controlled Hydraulic
Cooling Fan (Electronic Control Parts)
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5. INSPECT WATER TEMPERATURE SENSORUsing an ohmmeter, measure the resistance between the ter-
minals.
Resistance: 1.48±1.58 k
at 80 5C (176 5F)
If the resistance is not as specified, replace the sensor.
6. REINSTALL WATER TEMPERATURE SENSOR (a) Install a new O±ring to the water temperature sensor.
(b) Apply soapy water to the O±ring.
(c) Install the water temperature sensor to the radiator.
Torque: 7.4 N Vm (75 kgf Vcm, 65 in. Vlbf)
(d) Connect the water temperature sensor connector.
7. REFILL WITH ENGINE COOLANT (See page CO±7)
8. REINSTALL ENGINE UNDER COVER
9. RECONNECT CABLE FROM NEGATIVE TERMINAL OF BATTERY
(A/C High±Pressure Switch)
INSPECTION OF A/C HIGH±PRESSURE
SWITCH
1. DISCONNECT HIGH±PRESSURE SWITCH CONNECTOR
2. INSTALL MANIFOLD GAUGE SET (See AC section)
3. INSPECT HIGH±PRESSURE SWITCH(a) Wh e n th e A/C switch is OFF, ch e ck th a t th e re iscontinuity between terminals 2 and 3. (When the
pressure is 1,226 kPa (12.5 kgf/cm
2, 178 psi) or lower.)
(b) When the A/C switch and blower switch are ON, check
that there is no continuity between terminals 2 and 3.
(When the pressure is 1,520 kPa (15.5 kgf/cm
2, 220 psi)
or higher.)
If continuity is not as specified, replace the switch.
4. REMOVE MANIFOLD GAUGE SET
5. RECONNECT HIGH±PRESSURE SWITCH CONNECTOR
(Solenoid Valve)
(See page CO±36)
±
COOLIING SYSTEM Electronically Controlled Hydraulic
Cooling Fan (Electronic Control Parts)CO±63
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ENGINE TUNE±UP
INSPECTION OF ENGINE COOLANT
1. INSPECT ENGINE COOLANT LEVEL AT RESERVOIRTANK
The engine coolant level should be between the LOW and
FULL lines.
If low, check for leaks and add engine coolant up to the FULL
line.
2. INSPECT ENGINE COOLANT QUALITY There should not be any excessive deposits of rust or scales
around the radiator cap or reservoir tank filler hole, and the
engine coolant should be free from oil.
If excessively dirty, clean the engine coolant passages and
flush the cooling system.
INSPECTION OF ENGINE OIL
1. INSPECT ENGINE OIL QUALITYCheck the oil for deterioration, presence of water, discoloring
or thinning.
If the quality is poor, replace the oil.
Oil grade: API grade SG, Energy±Conserving II multi- grade. Recommended viscosity is as shown,
with SAE 5W±30 being the preferred engine
oil.
Drain and refill oil capacity:
w/ Oil filter change
4.8 liter (5.1 US qts, 4.2 lmp. qts)
w/o Oil filter change 4.5 liter (4.8 US qts, 4.0 lmp. qts)
2. INSPECT ENGINE OIL LEVELThe oil level should be between the ºLº and ºFº marks on the
dipstick.
If low, check for leakage and add oil up to ºFº mark.
±
ENGINE MECHANICAL Engine Tune±UpEM±7
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6. REPLACE ENGINE OIL AND OIL FILTER(See Lubrication System on page EG±497)
Oil grade:
API grade SG or SH, Energy±Conserving II or ILSAC
multigrade engine oil. Recommended viscosity is as
shown in the illustration, with SAE 5W±30 being the
preferred engine oil.
Drain and refill capacity:
w/ Oil filter change
4.8 liters (5.1 US qts, 4.2 lmp. qts)
w/o Oil filter change
4.5 liters (4.8 US qts, 4.0 lmp. qts)
7. REPLACE ENGINE COOLANT (See Cooling System on page EG±425)
Coolant capacity (w/ Heater):
10.8 liters (11.4 US qts, 9.5 lmp. qts)
HINT:
wUse a good brand of ethylene±glycol base coolant and
mix it according to the manufacturer's directions.
w Using coolant which includes more than 50 %
ethylene±glycol (but not more than 70 %) is
recommended.
NOTICE:
w Do not use a alcohol type coolant.
w The coolant should be mixed with demineralized water or
distilled water.
8. INSPECT CHARCOAL CANISTER
(a) Remove the charcoal canister.
(See Emission Control System on page EG±221)
(b) Visually inspect the canister case.
(c) Check for crogged each port and stuck check valve. wUsing low compressed air (4.71 kPa (48 gf/cm
2, 0.68
psi)), blow into port A and check that air flows without
resistance from the other ports.
w Blow low compressed air (4.71 kPa (48 gf/cm
2, 0.68
psi)) into port B and check that air does not flow from the
other ports.
If operation is not as specified, replace the charcoal canister.
±
MAINTENANCE (1UZ ± FE)MA±9
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COOLING SYSTEM
CO±1±
COOLIING SYSTEM Description
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DESCRIPTION
This engine utilizes a pressurized forced circulation cooling system which i\
ncludes a hermostat equipped
with a by±pass valve mounted on the inlet side. The cooling system is composed of the water jacket (inside the cylinder bl\
ock and cylinderhead), radiator,
water pump, thermostat, cooling fan, hoses and other components.
OPERATION
CO±2±
COOLIING SYSTEM Description
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DESCRIPTION
This engine utilizes a pressurized forced circulation cooling system whi\
ch includes a hermostat equipped
with a by±pass valve mounted on the inlet side. The cooling system is composed of the water jacket (inside the cylinder bl\
ock and cylinderhead), radiator,
water pump, thermostat, cooling fan, hoses and other components.
OPERATION
CO±2±
COOLIING SYSTEM Description
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Coolant which is heated in the water jacket is pumped to the radiator, through which a cooling fan blows
air to cool the coolant as it passes through. Coolant which has been coo\
led is then sent back to the engine by
the water pump, where it cools the engine. The water jacket is a network of channels in the shell of the cylinder bloc\
k and cylinderhead through which
coolant passes. It is designed to provide adequate cooling through the cylinders and combus\
tion chambers
which become heated during engine operation.
RADIATOR The radiator performs the function of cooling the coolant which has pass\
ed through the waterjacket and
become hot, and it is mounted in the front of the vehicle. The radiator consis\
ts of an upper tank and lower tank,
and a core which connects the two tanks. The upper tank contains the inlet \
for coolant from the water jacket
and the filler inlet. It also has a hose attached through which excess cool\
ant or steam can flow. The lower tank
contains the outlet for coolant and drain plug. The core contains many t\
ubes through which coolant flows from
the upper tank to the lower tank as well as cooling fins which radiate heat\
away from the coolant in the tubes.
The air sucked through the radiator by the cooling fan, as well as the wind generated by the ve\
hicle's travel,
passes through the radiator, cooling the coolant. Models with automatic transmission include an aut\
omatic
transmission fluid cooler built into the lower tank of the radiator. A cooling fan is mounted behind radiator to assist
the flow of air through the radiator. When the coolant temperature is low, the fan operates slowly to help the warm
up, and when the coolant temperature becomes high, the fan speed is increas\
ed to provide the air flow required
for cooling.
RADIATOR CAP (on Reservoir Tank)
The radiator cap is a pressure type cap which seals the radiator, resulting in pressurization of the radiator
as the coolant expands. The pressurization prevents the coolant from boi\
ling even when the coolant tempera-
ture exceeds 100 5C (212 5F). A relief valve (pressurization valve) and a vacuum valve (negati\
ve pressure valve)
are built into the radiator cap. The relief valve opens and lets steam esca\
pe through the overflow pipe when
the pressure generated inside the cooling system exceeds the limit (coolant temperature: 110±120 5C
(230±248 5F) pressure; 29.4±98.1 kPa (0.3±1.0 kgf/cm2, 4.3±14.2 psi)). The vacuum v\
alve opens to alleviate
the vacuum which develops in the coolant system after the engine is stopped\
and the coolant temperature
drops.
RESERVOIR TANK The purpose of the reservoir tank is to catch coolant overflows created by \
volumetrix expansion when the
coolant temperature increases. The cap of the reservoir tank is a pressure type\
which prevents deterioration
of the LLC (Long Life Coolant) caused by contact with atmospheric air, increases vaporization performance and
reduces loss of the coolant volume.
WATER PUMP The water pump is mounted on the front of the cylinder block and driven by t\
he reverse side of the timing
belt.
THERMOSTAT The thermostat has a wax type by±pass valve and is mounted in the wat\
er inlet housing. The thermostat
begins to open at the temperature of 80 5C (180 5F). When the coolant temperature is low, the valve closes to
prevent coolant flow to the radiator, thus permitting the engine to warm up rapidly. When the by±pass valve
opens the by±pass circuit, the engine coolant continues to circulate \
inside the engine, quickly and uniformly
warming up to the appropriate temperature. When the coolant temperature is high\
, the valve opens and coolant
flows to the radiator where it is cooled. When the wax inside the thermostat \
is heated, it expands and thus
creates pressure which overpowers the force of the spring which keeps the valve\
closed. When the wax cools,
its contraction causes the force of the spring to take effect once more, closing the valve.
ELECTRONICALLY CONTROLLED HYDRAULIC COOLING FAN (See page CO±22)
±
COOLIING SYSTEM DescriptionCO±3
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