Navigator 4WD V8-5.4L SOHC VIN L (1998)
Thermostat: Testing and Inspection
THERMOSTAT-WATER
The water thermostat should be replaced only after the following electrical and mechanical tests have been performed.
THERMOSTAT-ELECTRICAL TEST
CAUTION: Always vent the exhaust to the outside when performing this test.
NOTE: The electrical thermostat test is most accurate if performed indoors at less than 37.8°C (100°F) ambient air. This test may be performed with
or without the hood open and with the engine warm or cold.
1. Check the engine coolant level. Fill as needed.
2. With the ignition OFF, remove the Engine Coolant Temperature (ECT) sensor harness connector and attach ECT Sensor "T" Cable as a jumper
between the Powertrain Control Module (PCM) and the ECT Sensor. Attach the 73 Digital Multimeter to the ECT Sensor "T" Cable. Voltage
values (0-5 V) may now be monitored while the sensor retains its connection to the wiring harness.
New Generation STAR (NGS) Tester or the Service Bay Diagnostic System (SPUDS) may be used to monitor the ECT on vehicles equipped with
Data Link Connector (DLC). The SODS sequence to use for the screen is:
-
Toolbox-Electronic Engine Control and DCL-Item.
3. Place the transmission in PARK (Up) or NEUTRAL (N).
NOTE: Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause improper diagnosis.
4. Start the engine and allow the engine to idle throughout this test. Allow the engine to run for 2 minutes, then record the ECT voltage. Record the
ECT voltage every 60 seconds. When the ECT voltage trend changes direction or only changes slightly (0.03 voltage or less) from the previous
reading, record this as the thermostat opening voltage. Use the voltage and corresponding coolant temperature chart.
5. If the thermostat opening voltage is greater than 0.75 volts and less than 82°C (180°F), replace the water thermostat.
6. If the thermostat opening voltage is less than 0.75 volts and greater than 82°C (180°F), the water thermostat is good and should not be replaced.
For further instructions See: Testing and Inspection/Symptom Related Diagnostic Procedures
THERMOSTAT-MECHANICAL TEST
1. Remove the water thermostat.
2. Check the water thermostat for seating. Hold the water thermostat up to a lighted background. Leakage of light around the thermostat valve at
room temperature indicates that the water thermostat should be replaced. Some water thermostats have a small leakage notch at one location on the
perimeter of the thermostat valve, which is considered normal.
3. Immerse the water thermostat in a boiling antifreeze and water mixture.
4. See the General Specifications chart for water thermostat opening temperatures.