B4000 2WD V6-4.0L SOHC (2003)
Thermostat: Testing and Inspection
THERMOSTAT INSPECTION-4.0L
Electrical Test
Caution:
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Always vent the exhaust to the outside when performing this test.
Note:
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This 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
Note:
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Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause improper diagnosis
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.
3. Place transmission in Park (P) or Neutral (N).
4. Start the engine and allow the engine to idle throughout this test. Allow the engine to run for two 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 volt or less) from the previous
reading, record this as the thermostat opening voltage. Use the voltage and corresponding coolant temperature chart listed.
5. If the opening voltage is greater than 0.75 volt and less than 82.2°C (180°F) replace the thermostat.
6. If the opening voltage is less than 0.75 volt and greater than 82.2°C (180°F), the thermostat is good and should not be replaced.
Mechanical Test
1. Visually check that the thermostat valve is airtight.
2. Place the thermostat and a thermometer in water.
3. Heat the water and check the following.
Initial-opening temperature: 92°C -198°F) per 013-174.
Full-open temperature: 106°C (223°F).
Full-open lift: 3.2 mm (0.126 inch) minimum.
4. If the gasket surface of the thermostat is damaged, replace the thermostat.
