Coolant System Draining, Filling, and Venting

Draining the Coolant System

Tools needed:

• Flat-tip screwdriver with wide tip
• Containers to collect approximately 2 gallons (7.8 liters) of coolant
• Rags
• 10 mm socket, ratchet, and 6" extension (if belly pans not already removed)
• Phillips head screwdriver

Draining the cooling system on a 944 can be a messy job. Due to the position of the drain plug near the bottom radiator cross-member, coolant tends to drain into the cross-member and exit from holes at various locations along its underside — making it nearly impossible to avoid a mess. This is further complicated on turbocharged cars where the aerodynamic ground effects extend underneath the radiator.

To minimise draining problems, cut a piece of plastic (from an old antifreeze container or gallon milk jug) approximately 15 cm (6 inches) long and several centimetres wide (wider for turbo cars with ground effects). Fold the ends up to channel coolant, then tape the piece of plastic directly underneath the radiator drain plug using duct tape. The goal is to direct coolant from the plug toward your drain pan without letting it drip into the cross-member.

Caution: Keep children and pets away from antifreeze. It is toxic. Clean up spills promptly.

1. If the belly pans have not been removed, use the 10 mm socket and ratchet to remove the belly pan bolts. A Phillips head screwdriver may also be required on some cars.
2. Install the drip-directing device described above under the drain plug. Looking toward the front of the car, the drain plug is at the lower left (driver's side) corner of the radiator. It is normally blue in colour but may be discoloured with age.
3. Place a drain pan under the radiator and have rags ready.
4. Remove the cap from the coolant expansion tank.
5. Using the flat-tip screwdriver, remove the radiator drain plug. If the drain plug is badly discoloured, it is likely very old and brittle — antifreeze degrades plastic over time and they tend to break off during reinstallation. If the plug breaks off in the hole, it can usually be extracted with a small flat-tip screwdriver.
6. Draining via the radiator drain plug does not completely drain the cooling system. Coolant remains in the block around the cylinders. For procedures that require a complete drain (for example, when coolant and oil have mixed), there is a drain plug on the passenger's side of the block (left-hand-drive cars).

Radiator drain plug part numbers:

Model Year	Description	Part Number
83–86	Drain Plug M10 × 1 mm	944 106 353 00 *
87–91	Drain Plug M10 × 1.5 mm	944 106 353 01
ALL	Drain Plug Seal	944 106 354 00 **

* Also fits early 1987 924S ** Drain plug seal is included on late-model plugs

7. If coolant is to be reused, remove debris by straining the coolant through a funnel fitted with a screen or a paper towel.

Filling the Coolant System

Porsche recommends using a phosphate-free antifreeze in the aluminium engines used in 944s. Standard glycol antifreeze containing phosphates will cause minerals to plate out on the heat-transfer surfaces inside the engine, reducing cooling efficiency.

For most climates, a 50/50 mixture of antifreeze and distilled water is appropriate. In extremely hot or cold climates, consult the antifreeze manufacturer's instructions for the recommended ratio.

Tip: Look for antifreeze labelled specifically "Phosphate Free." The label claim "Safe for Aluminium Engines" does not guarantee the product is phosphate-free.

Venting the Coolant System

Tools needed:

• 12 mm socket and ratchet with extension
• Coolant system pressure tester (Method 1, preferred)

The coolant system vents best when at ambient temperature.

1. Turn the ignition key on and set the heater control to full heat (fully clockwise).
2. Crack open the coolant system high-point vent. This is a 12 mm bolt on the coolant nozzle at the front of the cylinder head, near the number 1 plug. On turbocharged cars, the bolt is on the side of the nozzle; on normally-aspirated cars it is on top.
3. Place catch rags around the vent.

Note: If the cooling system was completely drained (using the block drain plug), or if you have had trouble venting the system in the past, consider disconnecting the upper radiator hose at the radiator, holding it up in the air, and pouring coolant into the hose to fill the block directly. Open the high-point vent first so you can see when the block is full. Do not fill the hose completely — reconnect it to the radiator before it overflows — then continue to fill using one of the methods below.

Method 1 — Pressure Tester (Preferred)

a. Fill the coolant reservoir to between the minimum and maximum marks. b. Attach a coolant system pressure tester to the coolant reservoir. Many auto parts stores will loan the tool. c. Pressurise the system slowly until a steady stream of coolant issues from the vent. Do not exceed 10 psi. d. Close the vent.

Method 2 — Gravity Fill

a. Raise the front of the car on jack stands or ramps. b. With the high-point vent cracked open, slowly fill the coolant reservoir. c. When the reservoir is at or slightly above the maximum mark, coolant should begin to exit the vent. d. Continue filling until a steady stream flows from the vent. e. Close the high-point vent.

Note: Method 2 is less effective than Method 1. When venting is complete, the reservoir may contain more coolant than the system needs, causing overflow on the first drive as the coolant expands.

Note: The thermostat will not be open during initial fill, so the fill path runs via backflow from the upper radiator hose into the head and block — an inefficient path that may leave air voids. Run the engine until the thermostat opens to flush any remaining voids to the high point.

4. After initial venting is complete, start the car and run it until it reaches normal operating temperature. Set the temperature control to maximum heat — this opens the heater control valve and purges any air pocket in the heater core. After reaching operating temperature, vent the system again.