Pressure test
1. Turn off the engine.
2. Open the hood and install the protective covers on the fenders.
WARNING: Never remove the coolant expansion tank while the engine is running. Failure to follow these instructions may result in damage to the engine cooling system and personal injury. To avoid being scalded by hot water or steam from the cooling system, use extreme caution when removing the expansion tank from a hot cooling system. Wait until the engine has cooled, then place a thick cloth over the expansion tank cap and slowly turn it until the pressure begins to release. Move away from the expansion tank while releasing the pressure in the cooling system. When you are sure that all pressure has been released, twist and remove the expansion tank cap while keeping the thick cloth over it. Failure to follow these instructions may result in personal injury.
3. Carefully remove the expansion tank cap to relieve pressure in the cooling system. If necessary, top up the expansion tank with the correct coolant.
4. Install the pressure tester connector (ensuring tight connections) between the overflow/air purge nipple and the overflow/air purge hose in the expansion tank of the cooling system. Replace the expansion tank cap.
5. Connect the injection pump and pressure gauge to the connecting element and create a pressure in the cooling system, the value of which does not exceed the lower permissible limit for the expansion tank cap.
6. Observe the pressure gauge readings for approximately two minutes. During this period, the pressure should not drop.
- If the system holds pressure, proceed to step 8.
- If the pressure drops, check for leaks in the hoses from the engine to the heater core, from the engine to the radiator, the bypass hose, the water valve hose (if equipped), the thermostat housing gasket, the radiator core, the heater core, etc. If a leak in the cooling system cannot be found, also refer to the engine system checks. Repair any leaks found and recheck the system.
7. Release the pressure in the system by loosening the expansion tank cap. Check the coolant level. If necessary, add coolant of the correct concentration. For more information, refer to the information in this section.
8. Perform a pressure test of the coolant expansion tank cap in accordance with this section.
Pressure testing of the expansion tank cap of the cooling system
WARNING: Never remove the coolant expansion tank while the engine is running. Failure to follow these instructions may result in damage to the engine cooling system and personal injury. To avoid being scalded by hot water or steam from the cooling system, use extreme caution when removing the expansion tank from a hot cooling system. Wait until the engine has cooled, then place a thick cloth over the expansion tank cap and slowly turn it until the pressure begins to release. Move away from the expansion tank while relieving the cooling system pressure. When you are sure that all pressure has been released, twist and remove the expansion tank cap while keeping the thick cloth over it. Failure to follow these instructions may result in personal injury.
1. Carefully remove the expansion tank cap to relieve pressure in the cooling system. Add coolant to the tank if necessary.
2. Clean the rubber seal area and vacuum relief valve with water. Immerse the expansion tank cap in water and install the expansion tank cap pressure test adapter (included in the pressure tester) on the expansion tank cap.
NOTE: If the pump plunger is pressed too quickly, the pressure reading will be incorrect.
3. Slowly press the plunger of the pressure test pump until the pressure gauge reading stops increasing.
4. Record the highest pressure reading. Release the pressure by turning the pressure release screw counterclockwise. Then tighten the pressure release screw and repeat step 5 at least twice to check the stability of the pressure gauge reading and to ensure that the reading is within the acceptable range for the expansion tank cap.
5. If the pressure gauge reading is not within the range of the expansion tank cap, install a new expansion tank cap.
Checking the Thermostat
A new thermostat should only be installed after the following checks have been completed.
Electrical check of thermostat
WARNING: Always vent exhaust gases to the outside when performing this check. Failure to do so may result in personal injury.
NOTE: This procedure will provide the most accurate results when performed indoors with the ambient air temperature below 100°F (37.8°C). This test can be performed with the hood open or closed, and with the engine warm or cold.
1. Check the coolant level in the radiator and expansion tank of the cooling system. Top up the coolant if necessary.
2. With the engine off, disconnect the cylinder head temperature (CHT) sensor plug and connect the coolant temperature monitoring harness, using it as a jumper between the PCM and the CHT sensor. Connect a digital multimeter to the thermostat wiring. Voltage values (0 V to 5 V) can now be monitored without disturbing the sensor's wiring.
NOTE: Performing this test with the transmission in gear or the A/C compressor clutch engaged (running) will result in incorrect diagnosis.
3. Shift the transmission to position "P" (Park) or "N" (Neutral).
4. Start the engine and let it idle during this test. Let the engine run for 2 minutes, then record the TCT sensor voltage. Record the TCT sensor voltage every 60 seconds. When the overall trend of the TCT sensor voltage changes direction or the voltage changes only slightly (0.03 V or less) from the previous value, record that value as the thermostat opening voltage. Use the Voltage and Coolant Temperature Correspondence Table below.
| Coolant temperature°C (°F) | SNT (V) |
| 20 (68) | 3,09 |
| 40 (104) | 2,15 |
| 70 (158) | 1,04 |
| 80 (176) | 0,79 |
| 90 (194) | 0,61 |
| 95 (203) | 0,53 |
| 105 (221) | 0,41 |
5. If the thermostat opening voltage is greater than 0.79 V and the temperature is less than 80°C (176°F), install a new thermostat.
6. If the thermostat opening voltage is less than 0.79 V and corresponds to a temperature greater than 80°C (176°F), the thermostat is normal and does not need to be replaced. Refer to the Symptoms Chart for further instructions.
Mechanical check of thermostat
NOTE: Fully open means the thermostat valve rises above the seat by 5.8 mm or more.
Remove the thermostat and immerse it in a boiling mixture of antifreeze and water. The thermostat should begin to open when:
- 82°C (179°F) - vehicles with 1.6L Zetec-SE/1.4L engine.
- 82°C (179°F) - vehicles with 1.6L Duratec engine.
- 92°C (197°F) - vehicles with 1.8L/2.0L/1.6L Zetec-E engine.
- 87°C (188°F) - vehicles with 1.8L Diesel engine.
The thermostat should be fully open when:
- 96°C (204°F) - vehicles with 1.6L Zetec-SE/1.4L engine.
- 96°C (204°F) - vehicles with 1.6L Duratec engine.
- 99°C (210°F) - vehicles with 1.8L/2.0L/1.6L Zetec-E engine.
- 102°C (215°F) - vehicles with 1.8L Diesel engine.
Install a new thermostat if it does not work as directed:
- Vehicles with 1.6L Zetec-SE/1.4L engine. For more information, refer to Thermostat available in this section.
- Vehicles with 1.6L Duratec engine. For more information, please refer to Thermostat - 1.6L Duratec available in this section.
- Vehicles with 1.8L/2.0L/1.6L Zetec-E engine. For more information, refer to Thermostat available in this section.
- Vehicles with 1.8L Diesel engine For more information, refer to Thermostat available in this section.
- Vehicles with 2.0L Duratec ST engine For additional information, refer to Thermostat located in this section.
If the thermostat does not operate as designed, install a new thermostat. If there is no heat source to perform this test, check the thermostat for leaks. Hold the thermostat against a background light source. Light leaking through the new thermostat valve at room temperature indicates that a new thermostat should be installed. Some thermostats have a small amount of light leaking in one area around the perimeter of the thermostat valve, which is normal.
Checking for leaks in a radiator removed from a vehicle
CAUTION: Do not leak test an aluminum radiator with the same water that is used to leak test copper/brass radiators. The test water may contain flux and alkaline cleaners that will attack the aluminum.
Before starting the test, clean the radiator to prevent contamination of the test tank. The radiator leak test should be carried out in clean water at an air pressure of 138 kPa.
For aluminum radiators, it is recommended to use a separate clean test tank. If a separate tank for testing aluminum radiators is not available, the test tank should be washed each time before testing the aluminum radiator.
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