ATF Cooler Water Return Line. Porsche 996 Carrera 2 / Carrera 4 Tiptronic 1999–01  ›  99630707705

ATF Cooler Water Return Line. 

The Genuine Porsche ATF Cooler Water Return Line is a replacement coolant pipe used within the Tiptronic automatic transmission cooling system on applicable Porsche 911 (996) models.

Fits:

• Porsche 996 C2 3.4L 1999-08/01
• Porsche 996 C4 3.4L 1999-08/01
• Porsche 996 C2 3.6L 2001
• Porsche 996 C4 3.6L 2001
• Porsche 996 C4S 3.6L 2001 

Diagram Ref No 9

The line carries engine coolant away from the automatic transmission fluid (ATF) cooler after heat has been transferred between the transmission oil and the cooling circuit. By maintaining coolant circulation through the heat exchanger, it helps control automatic transmission fluid temperature and supports reliable Tiptronic gearbox operation.

It is important to note that 99630707705 carries coolant, not ATF itself. Porsche parts catalogues identify it specifically as the return-side water/coolant pipe within the Tiptronic ATF cooler assembly.

What This Product Does:

• Carries coolant away from the Tiptronic ATF cooler.
• Forms part of the automatic transmission temperature-control system.
• Allows coolant to circulate through the transmission heat exchanger.
• Helps control automatic transmission fluid temperature.
• Supports consistent Tiptronic gearbox operating temperatures.
• Maintains a sealed connection within the engine cooling circuit.
• Works with the ATF cooler and coolant supply line.
• Helps protect the transmission from excessive operating temperatures.
• Replaces a leaking, corroded, damaged or restricted original coolant pipe.

Symptoms Of Wear Or Failure:
Possible symptoms include:

• Visible coolant leakage.
• Coolant dripping beneath the vehicle.
• Gradual reduction in coolant level.
• Pink, red or white dried coolant residue around the pipe or connections.
• Coolant smell after driving.
• Dampness around hose or pipe joints.
• Corrosion on metal sections of the line.
• Cracking or deterioration around flexible sections or connections.
• Damaged or loose hose clamps.
• Coolant-system warning message or low coolant warning.
• Increasing engine coolant temperature if sufficient coolant is lost.
• Transmission temperatures becoming elevated if coolant circulation through the ATF cooler is compromised.
• Visible impact or underbody damage to the line.
• Kinking or deformation that restricts coolant flow.

Many of these symptoms can also originate from adjacent hoses, the ATF heat exchanger, seals or other cooling-system components, so the source of the leak should be confirmed before replacement.

Why Replacement Matters:
The Tiptronic transmission generates heat during normal operation. The ATF cooler helps regulate this temperature by transferring heat between the transmission fluid and the vehicle's cooling system.

For this process to work correctly, coolant must circulate freely through both the supply and return sides of the cooler.

A leaking or restricted return line can compromise this circulation and may cause:

• Loss of engine coolant.
• Reduced ATF cooling efficiency.
• Increased transmission operating temperatures.
• Increased strain on the cooling system.
• Coolant contamination around surrounding components.
• Engine overheating if coolant loss becomes severe.

Replacing a damaged line restores the intended coolant path and helps both the cooling and transmission systems operate correctly.

Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.

99630707705

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