Thermostat — General Information and Replacement

General Information

Overheating or overcooling problems may be caused by a faulty thermostat. A thermostat stuck open causes overcooling; a thermostat stuck closed, or one that opens at the wrong temperature, causes overheating.

There are two different thermostats for the 924S, 944, and 944 Turbo. The correct thermostat is determined by whether the car has a new-style or old-style water pump:

• Old-style water pump: the snap ring groove is 4.5 mm from the thermostat sealing surface inside the pump housing.
• New-style water pump: the groove is 7 mm from the sealing surface.

Parts

Part Number	Description	Application
944 106 129 05	Thermostat (Old-Style Water Pump)	924S, 944, 944 Turbo
944 106 929 05	Thermostat O-Ring (for thermostat 944 106 129 05)	924S, 944, 944 Turbo
944 106 019 00	Thermostat (New-Style Water Pump)	924S, 944, 944 Turbo
944 106 929 08	Thermostat O-Ring (for thermostat 944 106 019 00)	924S, 944, 944 Turbo
900 234 160 00	2.5 mm Support Washer (for thermostat 944 106 019 00)	924S, 944, 944 Turbo

Tools

• Flat-tip screwdriver
• 45° angle snap ring pliers
• Catch pan
• Catch rags
• Ramps or jack stands and floor jack
• 10 mm socket, ratchet, and 6" extension

Other Procedures Needed

• COOL-02, Coolant System Draining, Filling, and Venting

Replacement

1. Disconnect the battery negative lead.
2. Raise the front of the vehicle on ramps or jack stands.
3. Remove the belly pan.
4. Using COOL-02, drain the cooling system. Have a catch pan large enough for approximately 2 gallons of coolant, and have catch rags ready.
5. Remove the cooling hose going from the water pump to the bottom of the radiator.
6. Using angled snap ring pliers, remove the thermostat retaining snap ring. This can be very difficult and requires patience.
7. Remove the old thermostat. The thermostat has a sealing o-ring and, on new-style pumps, a spacer washer — both should come out with the thermostat.
8. If desired, test the old thermostat using the Testing procedure below.
9. Install the new thermostat with o-ring and support washer (if required) into the pump housing.
   • New-style water pump (7 mm gap): requires the new-style thermostat, new-style o-ring, and the 2.5 mm support washer between the snap ring and the thermostat.
   • Old-style water pump (4.5 mm gap): requires the old-style thermostat and o-ring; no support washer.
10. Install the snap ring. Orienting the holes in the snap ring toward the top or bottom of the pump housing will make future snap ring removal easier.
11. Install the cooling hose from the water pump to the radiator.
12. Using COOL-02, fill and vent the cooling system.
13. Connect the battery negative lead.
14. Start the vehicle and run until it reaches normal operating temperature. Check for leaks and verify correct thermostat operation.
15. Install the belly pan and lower the vehicle.

Testing

Tools needed:

• Cooking pot
• Thermometer
• Heat source (stove)

1. Remove the thermostat using the appropriate steps of the Replacement procedure above.
2. Inspect the thermostat for damage or excessive corrosion before testing.
3. Note the rated temperature stamped on the thermostat (likely in °C).
4. Place the thermostat in a pot of water. Insert a thermometer to monitor temperature.
5. Heat the water until it reaches the temperature stamped on the thermostat. At that temperature, the thermostat should be fully open.
6. Remove the heat source and allow the water to cool. The thermostat should be fully closed when the temperature drops to approximately 10° below the rated temperature.
7. If the thermostat does not operate as described, replace it.