Coolant System Draining, Filling, and Venting – 2.5L NA

Overview

This procedure guides you through draining, filling, and venting the coolant system on all Porsche 944 variants with an 8-valve engine, covering model years 1983–1988 (pre-1985.5 and 1985.5 onwards). Regularly maintaining the coolant system prevents overheating, ensures efficient engine cooling, and extends the life of engine components. The process involves removing old coolant, refilling with phosphate-free antifreeze, and venting air to avoid air pockets that can cause overheating.

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Tools Required

• Flat tip screwdriver with wide tip
• 10mm (3/8 inch) socket, ratchet, and 6-inch (150mm) extension (if belly pans are installed)
• Phillips head screwdriver
• 12mm (1/2 inch) socket, ratchet, and extension
• Coolant system pressure tester (optional, for Method 1)
• Jackstands or ramps (optional, for Method 2)

Parts Required

• Phosphate-free antifreeze (e.g., Prestone Extended Life), approximately 2 gallons (7.8 liters)
• Radiator drain plug (Pre-85.5): 944 106 353 00
• Radiator drain plug (85.5 Onwards): 944 106 353 01
• Radiator drain plug seal: 944 106 354 00

Step-by-Step Procedure

Step 1: Prepare for Draining

1. Park the car on a level surface and let the engine cool to ambient temperature.
2. Gather containers to collect approximately 2 gallons (7.8 liters) of coolant and have rags ready to clean spills.
3. Warning: Keep children and pets away from antifreeze, as it is toxic. Clean spills immediately.

Step 2: Remove Belly Pans (If Installed)

4. Use a 10mm (3/8 inch) socket, ratchet, and 6-inch (150mm) extension to remove the belly pan bolts. On some cars, a Phillips head screwdriver may also be needed.

Step 3: Set Up Coolant Channel

5. Cut a piece of plastic (e.g., from an old antifreeze container or milk jug) about 6 inches (150mm) long and several inches wide.
6. Fold the ends up to create a channel for the coolant.
7. Tape the plastic under the radiator drain plug (located at the lower left corner of the radiator, facing the front of the car) using duct tape to direct coolant into a drain pan, avoiding the radiator cross-member.
8. Place a drain pan under the radiator and have additional pans or rags ready to catch any spills.

Step 4: Drain the Radiator

9. Remove the cap from the coolant expansion tank.
10. Use a flat tip screwdriver to remove the radiator drain plug (typically blue but may be discolored).
11. Inspect the drain plug for brittleness or damage. If discolored or brittle, replace it with:
    For Pre-85.5 models:
    Radiator drain plug: 944 106 353 00 and seal: 944 106 354 00.
    For 85.5 Onwards models:
    Radiator drain plug: 944 106 353 01 (includes seal).
12. If the drain plug breaks off in the radiator, use a small flat tip screwdriver to remove the broken piece.
13. Allow the coolant to drain completely into the pan.
14. If reusing coolant, strain it through a funnel with a screen or a paper towel to remove debris.

Step 5: Drain the Engine Block (Optional)

15. If complete drainage is needed (e.g., for oil-coolant contamination), locate the drain plug on the passenger side of the engine block (left-hand drive cars).
16. Place a drain pan under the plug, remove it with a suitable wrench, and allow the coolant to drain.

Step 6: Prepare for Filling

17. Reinstall the radiator drain plug with its seal, ensuring it is secure but not overtightened.
18. If the block was drained, reinstall the block drain plug.
19. Ensure the car is at ambient temperature for optimal venting.
20. Turn the ignition key on and set the heater control to full heat (fully clockwise).

Step 7: Open the High Point Vent

21. Locate the high point vent (a 12mm bolt on the coolant nozzle at the front of the cylinder head, near the #1 spark plug). On NA models, it’s on top of the nozzle.
22. Use a 12mm (1/2 inch) socket and ratchet with an extension to crack open the vent bolt slightly.
23. Place rags around the vent to catch any coolant.

Step 8: Fill the Coolant System (Method 1 – Pressure Tester, Preferred)

24. Fill the coolant reservoir with a 50-50 mix of phosphate-free antifreeze and water to between the minimum and maximum marks.
25. Attach a coolant system pressure tester to the coolant reservoir.
26. Pressurize the system slowly (do not exceed 10 psi) until a steady stream of coolant flows from the high point vent.
27. Close the vent bolt and tighten to 10 Nm (7.4 ft-lbs).
28. Remove the pressure tester.

Step 9: Fill the Coolant System (Method 2 – Gravity Fill, Alternative)

29. Raise the front of the car on jackstands or ramps.
30. With the high point vent cracked open, slowly fill the coolant reservoir with a 50-50 mix of phosphate-free antifreeze and water.
31. Continue filling until the reservoir is at or slightly above the maximum mark and a steady stream of coolant flows from the vent.
32. Close the vent bolt and tighten to 10 Nm (7.4 ft-lbs).
33. Lower the car to level ground.

Step 10: Optional Block Filling (If Completely Drained)

34. If the system was completely drained or venting issues occurred previously, disconnect the upper radiator hose at the radiator.
35. Hold the hose upward and pour coolant into it while keeping the high point vent open.
36. Stop filling when a steady stream of coolant flows from the vent, then reconnect the hose.
37. Continue filling using Method 1 or Method 2.

Step 11: Flush the System

38. Start the engine and run it until it reaches normal operating temperature, keeping the heater control on maximum heat to flush the heater core.
39. Monitor the coolant level and add more if needed.
40. After the engine cools, repeat the venting process (Steps 7–9) to remove any remaining air pockets.

Post Procedure Checklist

• Check for coolant leaks at the radiator drain plug, block drain plug (if used), and high point vent.
• Verify the coolant level is between the minimum and maximum marks in the reservoir after cooling.
• Ensure all tools and debris are removed from the engine bay.
• Drive the car for 5 miles (8 km) and recheck the coolant level to confirm no air pockets remain.
• Inspect the radiator drain plug for signs of brittleness or damage, replacing if necessary.

Sources

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