Thermostat Replacement – 2.5L NA

Overview

This procedure outlines how to replace the thermostat in all Porsche 944 variants (8-valve engine) for pre-1985.5 and 1985.5 onwards models. The thermostat regulates engine coolant temperature, and replacing a faulty one prevents overheating or overcooling. Follow these steps carefully to ensure proper installation and cooling system performance.

Pink and blue text represent links to additional resources, tools, parts, and partner websites.

Tools Required

• Flat tip screwdriver
• 45° angle snap ring pliers
• Catch pan (for approximately 7.6 liters / 2 gallons of coolant)
• Catch rags
• Ramps or jack stands and floor jack
• 10mm (3/8 inch) socket, ratchet, and 150mm (6 inch) extension
• 10mm (3/8 inch) wrench

Parts Required

• Thermostat (Pre-85.5, old style water pump): 944 106 129 05
• Thermostat O-ring (for pre-85.5 thermostat): 944 106 929 05
• Thermostat (85.5 Onwards, new style water pump): 944 106 019 00
• Thermostat O-ring (for 85.5 onwards thermostat): 944 106 929 08
• 2.5mm support washer (for 85.5 onwards 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

Step 1: Prepare the Vehicle

1. Disconnect the negative battery lead to ensure safety during the procedure.
2. Raise the front of the vehicle using ramps or jack stands and a floor jack. Ensure the vehicle is secure before working underneath.
3. Remove the belly pan using a 10mm (3/8 inch) socket and wrench. Set the bolts aside for reinstallation.

Step 2: Drain the Cooling System

4. Place a catch pan capable of holding 7.6 liters (2 gallons) of coolant under the vehicle. Place catch rags around the work area to minimize spills.
5. Follow this link to ensure this step – Coolant System Draining, Filling, and Venting – of the process is followed accurately to drain the cooling system.
6. Remove the cooling hose connecting the water pump to the bottom of the radiator using a flat tip screwdriver to loosen the hose clamp. Allow any remaining coolant to drain into the catch pan.

Step 3: Remove the Old Thermostat

7. Using 45° angle snap ring pliers, carefully remove the thermostat retaining snap ring from the water pump housing. This may require patience due to limited access.
8. Remove the old thermostat, along with its O-ring and any spacer washer, from the water pump housing. Inspect the components for damage or wear.

Step 4: Install the New Thermostat

9. Install the new thermostat based on your model year:

For Pre-85.5 models:
Install the thermostat (944 106 129 05) with its O-ring (944 106 929 05) into the water pump housing. The groove for the snap ring is 4.5mm from the sealing surface.

For 85.5 Onwards models:
Install the thermostat (944 106 019 00) with its O-ring (944 106 929 08) and a 2.5mm support washer (900 234 160 00) into the water pump housing. The groove for the snap ring is 7mm from the sealing surface.

10. Install the snap ring into the water pump housing using 45° angle snap ring pliers. Orient the snap ring holes toward the top or bottom of the housing for easier future removal.

Step 5: Reassemble the Cooling System

11. Reinstall the cooling hose from the water pump to the radiator, securing it with the hose clamp using a flat tip screwdriver.
12. Follow this link to ensure this step – Coolant System Draining, Filling, and Venting – of the process is followed accurately to fill and vent the cooling system.

Step 6: Test and Finalize

13. Reconnect the negative battery lead.
14. Start the vehicle and let it run until it reaches normal operating temperature (approximately 80-90°C / 176-194°F). Check for leaks around the water pump and hose connections.
15. Reinstall the belly pan using a 10mm (3/8 inch) socket and wrench. Tighten the bolts to 10 Nm (7 ft-lbs).
16. Lower the vehicle from the ramps or jack stands.

Post Procedure Checklist

• Check for coolant leaks around the water pump, thermostat housing, and hose connections.
• Verify the engine reaches and maintains normal operating temperature (80-90°C / 176-194°F).
• Ensure all tools and debris are removed from the work area.
• Inspect the cooling hose and clamp for secure installation.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• YouTube

Note: To test the old thermostat, place it in a pot of water with a thermometer and heat it to the rated temperature (stamped on the thermostat, typically in °C). It should fully open at this temperature and close when cooled to approximately 10°C below the rated temperature. Replace if it does not function correctly.