This is the time of year when people write in about their leaking cooling systems, sudden loss of coolant, or failing radiators. It's also the time of year when lots of folks will be shopping for new headgaskets.
Your cooling system is a wear item. Radiators last a reliable eight years and then the plastic side tanks start embrittling, getting ready to crack at the worst possible time. Your heater water valve is plastic and after eight years is a time bomb. Hoses do wear out, usually cracking from the inside due to electrochemical deterioration, and they fail at the worst times as well.

Volvos last forever IF you replace critical parts BEFORE they fail. The most frequent and catastrophic failures are in the cooling system. If you own a Volvo over eight years old, give some serious thought to at least replacing the heater water valve and preferably all the hoses (including turbo oil cooler hoses) and the radiator as well. And change your coolant to keep the anticorrosion additives fresh. This is especially true for 960s with B6304 engines: one overheating episode and you've toasted the engine for good.