I don't think I ever replaced a radiator hose on my 95 850 and just did the upper hose on my 2000 S40. I'd wait for those to start leaking or show signs of failure (bulges) or when you need to drain the radiator for a repair (or when you want to do a flush) but there's no schedule I know of. For other things like belts, your timing belt (assuming you don't have a V8) is due at 10 years /120K miles so you will need to replace the timing belt, idler and tensioner. That's a good time to also replace the serpentine belts and inspect those idlers and pulleys since they come off to access the timing belt. Best thing to do is google for the S80 maintenance intervals and see when specific parts should be replaced. Usually its "inspect" for many rubber parts. Other things to do as preventative maint is keep clean fluids. You can do a coolant drain / distilled water flush /refill, you can do a brake fluid flush, a transmission drain/fill and refresh the power steering fluid (I use a turkey baster to suck out the fluid from the reservoir, refill, run the engine turning the wheels side to side then repeat 2-3 more times and you are done). Other things to take care of are the intake air filter and cabin air filter. Note not all Volvos have a fuel filter anymore... so that's not so critical but can be done. To keep your injectors clean, you can run a tank of 93 octane from a national brand each month or throw in a can of Techron injector cleaner from time to time (like when you do oil changes).