F 250 4WD Super Duty V10-6.8L VIN Y (2006)
Thermostat: Testing and Inspection
Thermostat - Coolant
A new coolant thermostat should be installed only after these electrical and mechanical tests have been carried out.
Thermostat, Electrical Test - 5.4L, 6.8L
CAUTION: Always vent the exhaust to the outside when carrying out this test.
NOTE: The electrical thermostat test is most accurate if carried out indoors at less than 37.8°C (100°F) ambient air. This test may be carried out
with or without the hood open and with the engine warm or cold.
1. Check the engine coolant level. Fill as needed.
2. A diagnostic tool may be used to monitor the cylinder head temperature (CHT) sensor on vehicles equipped with data link connector (DC).
3. NOTE: Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause incorrect diagnosis.
Place the 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 2 minutes, then record the engine coolant
temperature (ECT) voltage. Record the ECT sensor voltage every 60 seconds. When the ECT sensor 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.
5. If the thermostat opening temperature is less than 86°C (187°F) on 5.4L engines or 82°C (180°F) on 6.8L engines, install a new coolant
thermostat.
6. If the thermostat opening temperature is greater than 86°C (187°F) on 5.4L engines, 82°C (180°F) on 6.8L engines, the coolant thermostat is
good, a new thermostat should not be installed. GO to Symptom Chart for further instructions. See: Testing and Inspection/Symptom Related
Diagnostic Procedures/Diagnosis By Symptom
Thermostat - Mechanical Test
1. Remove the coolant thermostat.
2. Check the coolant thermostat for seating. Hold the coolant thermostat up to a lighted background. Leakage of light around the thermostat valve at
room temperature indicates that the coolant thermostat should be replaced. Some coolant thermostats have a small leakage notch at one location on
the perimeter of the thermostat valve, which is considered normal.
3. Immerse the coolant thermostat in a boiling antifreeze and water mixture.
4. Consult the General Specifications chart for coolant thermostat opening temperatures.
