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MNBoxster · 12-07-2006, 01:47 PM

Hi,

IMHO, if you have an early car and the Coolant Tank hasn't leaked, it's just because it hasn't leaked yet. The problem is not one of design, rather it stems from the type of Plastic used.

Over time, this plastic becomes unstable due to heat cycling. It off-gasses some of it's constituent chemicals resulting in a loss of plasticity, and subsequently cracks.

Back to your issue, you're correct, it is a Closed System, but it is also a pressurized system. The way that the system's pressure is regulated is to keep a specific air cavity in the Coolant Tank which is why the Fill mark is where it is.

As the Coolant heats and expands, it compresses this air cavity and at a certain point, pressure starts to build. But, if you reduce the size of this air cavity (by overfilling the system), you reduce the compressibility of it and the pressure rises higher than designed.

At this point, the system will seek to relieve the pressure and will likely seep Coolant (usually as steam) under the Coolant Cap seal, or past one of the system's Hose connections (which already aren't the strongest due to the Spring-type Clamps Porsche originally used).

A TSB directs that these Spring Clamps be replaced by Worm (Screw-type) Clamps whenever the opportunity presents itself such as when repairing, or draining the system. I suspect this is where the missing Coolant went, assuming that you eliminate a possibly cracked and leaking Coolant Tank as a cause.

A long-distance diagnosis is often very difficult, so while I don't think it's anything to worry about, I'd keep an eye on it for a couple weeks to confirm my speculation. Hope this helps...

Happy Motoring!... Jim'99

12-07-2006, 01:47 PM	#3
MNBoxster Registered User Join Date: Sep 2005 Location: Minneapolis/St. Paul, Minnesota, USA Posts: 3,308	Hi, IMHO, if you have an early car and the Coolant Tank hasn't leaked, it's just because it hasn't leaked yet. The problem is not one of design, rather it stems from the type of Plastic used. Over time, this plastic becomes unstable due to heat cycling. It off-gasses some of it's constituent chemicals resulting in a loss of plasticity, and subsequently cracks. Back to your issue, you're correct, it is a Closed System, but it is also a pressurized system. The way that the system's pressure is regulated is to keep a specific air cavity in the Coolant Tank which is why the Fill mark is where it is. As the Coolant heats and expands, it compresses this air cavity and at a certain point, pressure starts to build. But, if you reduce the size of this air cavity (by overfilling the system), you reduce the compressibility of it and the pressure rises higher than designed. At this point, the system will seek to relieve the pressure and will likely seep Coolant (usually as steam) under the Coolant Cap seal, or past one of the system's Hose connections (which already aren't the strongest due to the Spring-type Clamps Porsche originally used). A TSB directs that these Spring Clamps be replaced by Worm (Screw-type) Clamps whenever the opportunity presents itself such as when repairing, or draining the system. I suspect this is where the missing Coolant went, assuming that you eliminate a possibly cracked and leaking Coolant Tank as a cause. A long-distance diagnosis is often very difficult, so while I don't think it's anything to worry about, I'd keep an eye on it for a couple weeks to confirm my speculation. Hope this helps... Happy Motoring!... Jim'99 Last edited by MNBoxster; 12-07-2006 at 02:32 PM.