Coolant System Draining, Filling, and Venting

Overview

This procedure explains how to drain, fill, and vent the coolant system on your Porsche 944 S2 with its 3.0L engine. It’s essential for maintenance tasks like replacing coolant, fixing leaks, or addressing oil-coolant mixing. Doing it right keeps your engine cool and prevents air pockets that could cause overheating.

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Tools Required

• Flat-tip screwdriver (wide tip)
• Containers to collect 2 gallons (7.8 liters) of coolant
• Rags
• 10mm (3/8 inch) socket, ratchet, and 6-inch (152 mm) extension (if belly pans are installed)
• Phillips-head screwdriver
• 12mm (1/2 inch) socket, ratchet, and extension (for venting)
• Coolant system pressure tester (optional, for Method 1)
• Jackstands or ramps (optional, for Method 2)
• Funnel with screen or paper towel (if reusing coolant)

Parts Required

• Phosphate-free antifreeze (e.g., Prestone Extended Life) – about 2 gallons (7.8 liters) for a 50-50 mix
• Radiator drain plug (if replacing) – 944 106 353 01 (M10 x 1.5mm for 1989-1991 S2)
• Radiator drain plug seal – 944 106 354 00

Step-by-Step Procedure

1. Draining the Coolant System

1. Park your Porsche 944 S2 on a level surface and let the engine cool to ambient temperature.
2. If the belly pans are still attached, remove them using a 10mm (3/8 inch) socket, ratchet, and 6-inch (152 mm) extension. Some cars may also need a Phillips-head screwdriver for additional screws.
3. Cut a piece of plastic (e.g., from an old antifreeze jug) about 6 inches (152 mm) long and 3-4 inches (76-102 mm) wide. Fold the ends up to make a channel, then tape it under the radiator drain plug with duct tape. This directs coolant into your container and reduces mess.
4. Place a large drain pan (or several smaller ones) under the radiator’s lower left corner (facing the front of the car). Have rags ready to catch spills.
5. Remove the cap from the coolant expansion tank to release pressure.
6. Locate the blue radiator drain plug at the bottom left of the radiator. Use a flat-tip screwdriver to carefully unscrew it. If it’s brittle or discolored, replace it with 944 106 353 01 and a new seal, 944 106 354 00.

7. Let the coolant drain fully into your containers. Note: This won’t empty the engine block completely—only the radiator and some hoses drain this way.
8. (Optional) For a full drain (e.g., if oil mixed with coolant), find the drain plug on the passenger-side engine block (right side for left-hand drive cars). Unscrew it with a suitable wrench and drain the remaining coolant.
9. If reusing coolant, strain it through a funnel with a screen or a paper towel to remove debris.
10. Wipe up any spills immediately—antifreeze is toxic to kids and pets.

2. Filling the Coolant System

11. Mix phosphate-free antifreeze (like Prestone Extended Life) with water in a 50-50 ratio—about 2 gallons (7.8 liters) total. Adjust the mix if you live in extreme heat or cold (check the antifreeze label).
12. Disconnect the upper radiator hose from the radiator, lift it up, and pour coolant into the hose until the block fills and coolant flows steadily from the high-point vent (step 14). Reconnect the hose afterward.
13. Otherwise, pour the coolant mix into the expansion tank until it’s between the minimum and maximum marks.

3. Venting the Coolant System

14. Turn the ignition key to “on” (don’t start the engine) and set the heater to full heat (turn the dial fully clockwise).
15. 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 the S2, it’s on top of the nozzle. Crack it open slightly with a 12mm (1/2 inch) socket and ratchet, and place rags around it to catch drips.
16. Choose one of these venting methods:
    Method 1 (Preferred): Attach a coolant pressure tester to the expansion tank. Slowly pressurize to no more than 10 psi until a steady stream of coolant flows from the vent. Close the vent with the 12mm (1/2 inch) socket.
    Method 2: Raise the front of the car on jackstands or ramps. Slowly fill the expansion tank until coolant flows steadily from the vent. Close the vent when done. Note: You may need to drain excess coolant later if the tank overflows.
17. Start the engine and let it run until it reaches normal operating temperature (thermostat opens). Keep the heater on max to flush the heater core.
18. Turn off the engine, let it cool slightly, then repeat steps 15-16 to vent any remaining air.
19. Top off the expansion tank to between the minimum and maximum marks if needed.

Post Procedure Checklist

• Check for leaks around the radiator drain plug, block drain plug (if used), and high-point vent.
• Ensure the expansion tank level stays between the minimum and maximum marks after driving.
• Verify the engine runs at normal temperature without overheating.
• Dispose of old coolant safely at a recycling center.

Sources

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