Adding coolant question???/

[Perfectlap]

make sure you are topping with the same kind of coolant that is in there already.
If you mix long-lasting expensive coolant with the generic kind you'll degrade the protective additives. Wayne Dempsey in 101 Boxster Projects actually advocates keeping the coolant 2 years fresh to maintain this protection.

And when flushing and old tank make sure all the air is out. Otherwise you'll be paying for a second fill up because the old, brittle tank split from the air pressure and dumped all your expensive coolant onto the street. Coolant flush usually runs about $400 with these cars.