There is no pre-defined replacement period on the coolant, They recommend checking the coolant every 20K miles and replacing as needed. Chances are by the time the coolant is bad you'll have a reason (water pump, leak) to change it anyway.

 

Yes it's true but if the bad coolant water is the cause of pump problem ?
Do you think it's necessary put stop-leak ?

 

Yes, things that impact the coolants lubricating qualities can absolutely cause premature failure of the water pump. .But Porsche had a lot of waterpump quality issues around this time frame, so it's also possible it's just a poor design. No, stop leak is not generally required for a healthy cooling system. It's just going to mask a problem. If the problem is small, or like jzchen you need to defer a problem, it can be a great option but there should be no reason to use it proactively and it won't help stop future issues.

 

Thanks for your answer