THERMOSTAT INSPECTION [YF (2.0L Zetec), AJ (3.0L Duratec)]

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Thermostat Electrical Test

Note

• The electrical thermostat test is most accurate when performed indoors at less than 37.8 °C {100 °F} ambient temperature. This test may be carried out with or without the hood open and with the engine warm or cold.

1. Inspect the coolant level. Add coolant if necessary.

2. Connect the SST (WDS) or equivalent to the DLC-2.

3. Monitor the PID using the PID/data monitor function.

4. Place the transaxle in P or N position.

Note

• Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause incorrect diagnosis.

5. Start the engine and allow the engine to idle throughout this test. Allow the engine to run for 2 min, then record the ECT voltage. Record the ECT voltage every 60 s. 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 below.

Coolant temperature (°C {°F})

ECT voltage (V)

22 {72}

3.00

43 {109}

2.01

71 {160}

1.01

82 {180}

0.75

91 {196}

0.59

97 {207}

0.50

105 {221}

0.40

Coolant temperature (°C {°F})	ECT voltage (V)
22 {72}	3.00
43 {109}	2.01
71 {160}	1.01
82 {180}	0.75
91 {196}	0.59
97 {207}	0.50
105 {221}	0.40

6. If the thermostat opening voltage is more than 0.75 V and less than 82 °C {180 °F}, install a new thermostat.

7. If the thermostat opening voltage is less than 0.75 V and more than 82 °C {180 °F}, the thermostat is normal and should not be replaced.

• If there is a malfunction, replace the thermostat.

Thermostat Mechanical Test

1. Remove the thermostat. (See THERMOSTAT REMOVAL/INSTALLATION [AJ (3.0L Duratec)].) (See THERMOSTAT REMOVAL/INSTALLATION [YF (2.0L Zetec)].)

2. Inspect the thermostat for sealing. Hold the thermostat up to a lighted background. Leakage of light around the thermostat valve at room temperature indicates that thermostat should be replaced. Some thermostats have a small leakage notch at one location on the perimeter of the thermostat valve, which is considered normal.

3. Immerse the thermostat in a boiling antifreeze and water mixture.

4. Inspect the thermostat for the following items:

• A closed valve at room temperature

• The opening temperature and lift of the valve

― If there is any malfunction, replace the thermostat.

Condition

Specification

YF (2.0L Zetec)

AJ (3.0L Duratec)

Initial-opening temperature

(°C {°F})

90—94 {194—201}

90—93 {194—199}

Full-open temperature

(°C {°F})

106 {223}

Full-open lift

(mm {in})

9 {0.35} or more

7.3 {0.29} or more

Condition		Specification
Condition		YF (2.0L Zetec)	AJ (3.0L Duratec)
Initial-opening temperature	(°C {°F})	90—94 {194—201}	90—93 {194—199}
Full-open temperature	(°C {°F})	106 {223}
Full-open lift	(mm {in})	9 {0.35} or more	7.3 {0.29} or more