a response ....

Thought I might tackle this on the weekend, or there abouts. Was not looking forward to removing the hardtop and putting the top in "service position" , but there is no time like the present. The tank has 10 years and almost 60k on it which is enough service life out of it for me to replace it with the newer version(see pic). We are probably lucky to get what we have out of the old tank. Sunset had a sale($208.16, list $336.00=ouch) on them, so I thought it was a decent time to pick one up. Have a set of remote spring clamp pliers ready to go to tackle the fun task of getting at those nasty clamps. I'll see if I can take some pics during the process.
regards

... mine is 13.5 years old with over 205,000 miles and is still the OEM.
As I've stated in the past, I truly believe that most of the failures are due to over expansion of the plastic due to air in the system.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 311,000+ miles: [www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

The earlier versions seemed to be worse then the later, but It has been my experience that they have a limited life and the warning signs are not totally transparent(partially due to location). If you have that many miles on it, then good for you. Personally, it is not worth risking the family getting stuck out here where service is not easy. In my view, the life of these coolant tanks depends on a number of varying factors:
-service life
-production date
-type of driving
-where it is driven(hot or cold climates)
You get the idea. Overall, I believe these cars run on the hot side and tend to cycle a lot. We've done a number of mods(3rd rad, 996 oil cooler, etc.) to counter this which I believe is helpful when sitting in stop and go traffic during the summer months. I've seen too many failures to for go the risk of an unexpected breakdown. Generally, I find on the VW/Audi marks(coolant tank is easily visable for cracking/leakage), 60k is a safe time for replacement before letting it go till the end of the service life when more damage could be risked. Even if the tank blows from air in the system, they should have the integrity to bleed that air from the system, and or the coolant system is being improperly serviced. It just shows the loss of structural integrity of the tank through the heat cycling. $208 for me, is cheap insurance towards reducing unexpected breakdowns. In my view, plastics have there limitations, especially as they age.
regards

at a seam and I think it is due to mainly material fatigue Sure the tank sees some pressure then the pressure drops but the build up is rather relaxed and so's the drop off.

Best thing I think one can do is try to install the new tank in such a manner it is properly hung/supported and is under no twist. Even if this means perhaps putting a washer shim behind one or more places where the thing attaches to the car to avoid putting the tank in the car under some stress. This will tend to accelerate the tendency for the tank to let go at a seam.

Sincerely,

MarcW.

I am in the process of doing this as we speak. We difficult to get at claps. Going to sears to get remote hose clamps. Will post update.