I thought it was weird when I read my Mercedes owners manual and saw that the coolant was good for 143,000 miles. I ignore Mercedes on every other service interval, so why not coolant too? But then I read the Cayman's owners manual and Porsche goes even a step beyond MB and says the coolant is the "permanent type", and there isn't a recommended change interval. Porsche coolant is apparently forever.

I don't buy it. I find it especially disconcerting that a company that specialized in air-cooled engines for decades becomes the first auto manufacturer (that I'm aware of) to introduce permanent coolant. Since Porsche says you can top off the coolant with water I assume they used one of the Ethylene Glycol variants.

I was always taught that heat breaks down Ethylene Glycol over time, so that even if you have an engine and radiator made from aluminum and plastic you still need to change the coolant after 3-5 years. I'm curious - why is the Cayman different?

Well, just to top off my CS, I bought a gallon of the super-duper, "permanent-type" coolant from Sunset Porsche. There's nothing magic about this stuff. It looks like a typical ethylene glycol / diethylene glycol, non-silicate coolant. (BMW, for example, sticks to silicate type, so don't interchange usages.)

The non-silicate, or Organic Acid Technology (OAT), coolants, theoretically last longer than the silicate types, but I'm not comfortable leaving that coolant in my CS forever. One thing is CERTAIN - don't let your coolant get low. Keep it topped off. The Cayman cooling system has such a long, complex circuit there could be very minor leaks just about anywhere under that chassis tray, and you'd never know it, so I recommend checking the coolant level at least monthly.

Also, I'm going to change my coolant about every three years. No way am I believing in "permanent". If you lease or trade often, never mind. I'm guessing a Cayman coolant flush is an expensive PITA (though I don't know the procedure yet).