Thermostat Replacement

Overview

This procedure covers the replacement of the thermostat on a Porsche 944 S2 with a 3.0L engine. The thermostat regulates coolant flow to keep the engine at the right temperature. A faulty thermostat can cause overheating (if stuck closed) or overcooling (if stuck open), both of which can harm engine performance. This guide focuses on the S2, which uses the newer-style water pump with a 7mm gap between the sealing surface and snap ring groove.

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Tools Required

• Flat tip screwdriver
• 45° angle snap ring pliers
• Catch pan (large enough for 2 gallons (7.6 liters) of coolant)
• Catch rags
• Ramps or jack stands and floor jack
• 10mm (3/8 inch) socket, ratchet, and 6-inch (152mm) extension
• Cooking pot (for testing)
• Thermometer (for testing)
• Heat source like a stove (for testing)

Parts Required

• Thermostat (New Style Water Pump) – 944 106 019 00
• Thermostat O-Ring (for new style thermostat) – 944 106 929 08
• 2.5mm Support Washer (for new style thermostat) – 900 234 160 00

Required Additional Procedures

Steps in these procedures are required to complete this process:

• Coolant System Draining, Filling, and Venting

Step-by-Step Procedure

1. Prepare the Vehicle

1. Disconnect the negative battery lead to ensure safety while working on the cooling system.
2. Raise the front of the Porsche 944 S2 using ramps or jack stands and a floor jack. Secure the vehicle properly.
3. Remove the belly pan under the engine bay using a 10mm (3/8 inch) socket, ratchet, and 6-inch (152mm) extension.

2. Drain the Cooling System

4. Follow this link to ensure this step – Coolant System Draining, Filling, and Venting – of the process is followed accurately. Place a catch pan under the radiator to collect about 2 gallons (7.6 liters) of coolant. Use catch rags to clean up any spills.

3. Remove the Old Thermostat

5. Locate the cooling hose connecting the water pump to the bottom of the radiator. Use a flat tip screwdriver to loosen the hose clamp and remove the hose.
6. Use 45° angle snap ring pliers to remove the thermostat retaining snap ring from the water pump housing. This can be tricky, so take your time and be patient.
7. Pull out the old thermostat, along with its o-ring and support washer, from the water pump housing.

4. Install the New Thermostat

8. Insert the new thermostat (944 106 019 00) with its o-ring (944 106 929 08) and 2.5mm support washer (900 234 160 00) into the water pump housing. The S2’s newer-style water pump requires the support washer due to the 7mm gap between the sealing surface and snap ring groove.
9. Secure the thermostat with the snap ring using the 45° angle snap ring pliers. Position the snap ring holes toward the top or bottom of the housing for easier future removal.

5. Reassemble and Refill

10. Reattach the cooling hose from the water pump to the radiator and tighten the clamp with a flat tip screwdriver.
11. Follow this link to ensure this step – Coolant System Draining, Filling, and Venting – of the process is followed accurately to refill and vent the cooling system.
12. Reconnect the negative battery lead.

6. Test the System

13. Start the engine and let it run until it reaches normal operating temperature (about 80-90°C or 176-194°F).
14. Check for coolant leaks around the water pump and hose connections.
15. Reinstall the belly pan using the 10mm (3/8 inch) socket, ratchet, and extension, then lower the vehicle from the ramps or jack stands.

7. Optional: Test the Old Thermostat

16. Fill a cooking pot with water and place the old thermostat in it.
17. Use a thermometer to monitor the water temperature. Heat the pot on a stove until it reaches the thermostat’s rated temperature (stamped on the thermostat, typically in °C).
18. Check if the thermostat fully opens at this temperature. Let the water cool to about 10°C (18°F) below the rated temperature and confirm it fully closes. If it doesn’t work as expected, discard it.

Post Procedure Checklist

• Check for leaks around the water pump and cooling hose.
• Verify the engine reaches and maintains normal operating temperature.
• Ensure the belly pan is securely reinstalled.

Sources

• Clark’s Garage – Thermostat – General Information and Replacement
• Pelican Parts – Porsche 944 Technical Articles
• Porsche 944 Workshop Manual, Volume 2
• Rennlist Porsche 944 Community Forums