combined sensor? SC2: "post update"

Hello, I posted earlier about a coolant temp., coolant level, trans.
axle warning light. One sensor for all of these. Also stating that my
coolant level was not low, even in the overflow tank, the temp. of
coolant was not excessively hot (observing the coolant guage needle),
and that the trans. axle fluid couldn't be over heated because the
warning light comes on too soon.
I did, originally, look under the car for a coolant leak but didn't
see any signs of one. Tonight I, three weeks later, decided to look
again and there is a coolant leak, but it is so small it never drips
onto the ground. There are just very small drips on the plastic under
the radiator. The overflow tank is now under it's proper fill level.
Could the coolant low level sensor be so sensitive that when the car
gets hot and a little coolant leaks out of the radiator, the warning
light starts to flash, the engine then sucks a little bit of fluid from
the overflow tank and the warning lights go out? Then the cycle keeps
repeating. Finally showing up as low coolant in the overflow tank.
Car is a '97 SC2 w/50k miles. Original owner and very well
maintained.
Dan.

 

1998 Saturn S-Series

Cooling System Description
Cooling Fan Motor Control

The PCM controls the cooling fan motor by controlling the cooling fan
relay. The PCM controls the cooling fan relay by controlling an internal
driver that pulls the relay coil circuit to ground. When the relay coil
circuit is pulled to ground, the switch side of the relay closes
allowing current to flow to the cooling fan motor.

The PCM turns the cooling fan relay ON based on the reading from the
engine coolant temperature (ECT) sensor. The ECT sensor is a thermistor
that varies resistance according to changes in engine coolant
temperature. The PCM supplies a 5 volt reference through a pull-up
resistor to the sensor, which is connected to ground. When the sensor is
cold, it has high internal resistance, high signal voltage at the PCM.
As the sensor temperature increases, its resistance decreases, a low
signal voltage at the PCM. The PCM uses the signal voltage to determine
the engine coolant temperature.

Under normal operating conditions, the cooling fan motor operates
whenever the ECT is greater than 105.5°C (222°F) or the A/C relay is
commanded ON below 113 km/h (70 mph). The cooling fan motor will turn
OFF when the temperature drops below 100°C (212°F). If the engine is
turned OFF and the ECT is above 107°C (225°F), the cooling fan motor can
run up to 4 minutes or run until the ECT drops below 107°C (225°F) with
the ignition OFF. If a low/high ECT circuit fault resulting in DTC P0117
or P0118 is set, the PCM will command the cooling fan relay ON to
protect the engine and transaxle until the condition is corrected.
Coolant Temp Gage

The PCM controls the coolant temp gage by sending a gage position
message to the instrument panel (IP) cluster over the Class II link. The
PCM receives the engine coolant temperature from the ECT sensor. The
gage position for the temperature is buffered, which means the
temperature is averaged over a period of time. This allows the gage to
move slowly and remain in a relatively stable position as the
temperature varies while driving.
Coolant Temp Telltale

The coolant temp telltale is used to alert the driver that the engine or
transaxle may be in an overheated condition. The PCM controls the
coolant temp telltale by sending a message over the Class II link to the
I/P cluster to turn the telltale ON. The PCM will command the telltale
ON when the ECT sensor reading is above 118°C (244°F) or the transaxle
fluid temperature (TFT) sensor reading is above 140°C (284°F). If this
condition exists, the PCM will set DTC P0217 for the ECT and P0218 for
the TFT. If a low or high voltage circuit fault exists in either
circuit, the signal will be invalid and the PCM will NOT turn ON the
coolant temp telltale. The malfunction indicator lamp (MIL) and engine
cooling fan relay will be command ON, however.
Coolant Level Telltale

The coolant level telltale is used to alert the driver that the coolant
level in the coolant recovery reservoir is low. Low coolant level is
detected by the low engine coolant level switch in the bottom of the
coolant surge tank. The switch closes when the coolant level in the
bottle is full. The switch is supplied ignition voltage from the UHFB
and this ignition voltage input is fed directly to the PCM. If the
engine is running and the voltage at the PCM is low, indicating no
coolant in the coolant surge tank, switch open, the PCM will command the
I/P cluster over the Class II link to turn the coolant level telltale
ON. If this condition exists for a certain length of time, the PCM will
set DTC P1620.
Scan Tool Diagnostics

* The engine coolant temperature (ECT) can be read on the scan tool
in degrees C or F.
* LOW COOLANT LEVEL can be read on the scan tool as YES or NO.
* The scan tool can "Sweep" all gages to verify the coolant temp
gage can move from cold to hot.
* The scan tool can turn ON all I/P cluster lights to verify the
coolant temp telltale can be turned ON and OFF.

Cooling System

Object Number: 872988 Size: MF
Click here for detailed picture of above image.

The Saturn cooling system has two unique features, a coolant surge tank
and an inlet side thermostat. The system is filled through the pressure
cap and doesn't require any bleeding. Flow from the tank fills the
engine cylinder block, radiator, heater core, and hoses.

During engine operation with the thermostat closed, coolant is pumped
through the cylinder block, cylinder head, heater core inlet hose,
heater core, heater outlet hose, and back to the thermostat housing.
Coolant flows past the thermostat element and back to the water pump
inlet. Some coolant is routed back through the engine block to the
thermostat cavity. A thermostat by-pass valve controls return coolant
flow through the cylinder block and dampens sudden coolant pressure
surges by venting coolant back to the water pump suction side.

When the thermostat begins to open the by-pass valve begins to close the
cylinder block passage. Coolant flow is then routed from the pump
through the cylinder block, head, heater inlet, heater core, heater
outlet, and back to the cylinder block. Coolant is also routed through
the upper radiator hose, radiator core, lower or outlet radiator hose
past the thermostat to the water pump. Coolant flow from the heater
return and lower radiator hose wash the thermostat element, thus
regulating coolant flow through the lower radiator hose and to the water
pump.

Important

During extremely cold weather, -12°C (+10°F) or colder, the engine's
coolant temperature will decrease quickly when idling with the heater
fan on high speed, and cool air may flow from the heater outlet.

The fan control switch should be set at a slower speed position, fan
speed I or II, to maintain the hottest air flow.

The Saturn cooling system is filled with DEX-COOL=3F, a non phosphate,
silicate free ethylene glycol-based antifreeze recommended for aluminum
engine protection and increased water pump seal life.
Coolant Surge Tank

Object Number: 872303 Size: MF
Click here for detailed picture of above image.

The coolant surge tank is made of molded plastic. It incorporates a low
coolant sensor. This sensor is designed to signal a low coolant level
within the reservoir through a light on the dash. A magnetic float
assembly moves up and down with the coolant. An electrical switch is
held in the closed position by the magnetic float. When the coolant
level drops below a pre-determined point, the float assembly drops and
opens the switch, which triggers the low coolant light.
Engine Cooling Fan

Object Number: 873183 Size: MF
Click here for detailed picture of above image.

The A/C fan is 290 mm (11.6 in) long with five unequally spaced blades
to provide air flow through the radiator/condenser. The fan is driven by
an electric motor which is attached to the fan shroud.

A fan control relay is used by the PCM to control engine cooling fan
operation. The engine cooling fan is turned ON or OFF by the PCM
dependent upon engine coolant temperature, vehicle speed, or A/C ON
request. Under high ambient conditions, the fan may run up to four
minutes with the key OFF.
Radiator

Object Number: 872929 Size: MF
Click here for detailed picture of above image.

A cross-flow radiator is used on all models. Tanks on this type radiator
are located to the right and left of the core.

All service radiators have oil coolers with inlet outlet fittings for
transaxle fluid circulation. On vehicles equipped with a manual
transaxle, keep plugs on cooler fittings.

 

it was the radiator. Leaking so slowly at first that it didn't even
drip onto the ground. Just evaporated from the heat of the engine.
Eventually it was leaking enough to start dripping onto the ground.
Took it in and the shop dude said it was the radiator where the metal
part of the radiator is attached to the plastic part. Maybe I'm behind
the times but when did plastic start to become part of a radiator?

 

My 1981 Dodge Grand Caravan had a plastic radiator that lasted ~100,000
miles.