HenryPcar

Regardless of the pros and cons of reservoir or expansion tank, the fact is the Porsche tanks are under pressure and are known to crack. This are the same with BMWs also and they are notorious to get you stranded when they burst....and it happens way too often because the bottle is plastic and when it ages we all know the weakness of such design. A simple design change to whatever the Japanese system uses will solve that problem altogether. The radiators are under pressure, but not their overflow tanks and they rarely seldom crack. That is what I was trying to point out, but the other party insist on the venting of the pressure at the highest point which has nothing to do with this thread at all.

Ahsai

The article clearly explains why the 996 requires an expansion tank and not a recovery tank like you proposed.

"In many modern cars the radiator is mounted lower than the engine. Since the radiator is lower than the engine a pressure relief and fill point that is higher than the engine is needed. This is accomplished with an expansion tank. When the radiator is high enough to act as a fill point and pressure relief an expansion tank is not necessarily required. In those applications a recovery style tank may be used instead. "

sweet victory

You realize that it isn't a simple design change though, right? You would need to raise the top of the radiator above the engine and add a radiator cap. Not only is the car now going to look terrible, you'd need to remove the front bumper to add coolant.

If you can't understand this, I don't know what to tell you.

HenryPcar

Perhaps, but this is not a unique Porsche problem. BMWs are prone to bursting their coolant bottles under pressure and their radiators are located conventionally, not like the 911s with plumbing routed all the way to the back. If it is necessary to have an expansion tank, at least use metal instead of plastic. As it is now, for such a critical function as engine cooling, if it is busted out there you are stranded. But then you will have those vouching for Porsche's engineering aptitude to say "it is better that their expansion tank blows instead of their radiator while under extreme pressure. My point here is, it is a half-*** under engineered system and those that side with Porsche's engineering aptitude will always vouch for them regardless.

Ahsai

I have some sympathy for your comment but I don't think anyone is saying Porsche coolant system design in the best in the world. Rather, people are just trying to point out there's a reason for this specific design choice. It's just another engineering problem full of compromise.
If cost and weight were no objects, I'm sure they will put a metal coolant tank, which will never crack. I have complained a lot of times about their IMSB, oil pressure sensor, window regulator, etc myself. Regarding that tank, just replace it every 4~5yrs it's not so bad.