Use the stock Volvo coolant and distilled water. Remember, the coolant is not only for heat transfer but also has anti-corrosion additives. And by changing it regularly, you clean out contaminants and sludge (if any). Well-worthwhile and cheap maintenance. My mechanic here in town curses cars where the coolant has never been changed because he often has to replace the entire radiator and other parts because they are so gunked up.