Well I can't buy the 10 degree cooler line, the vehicle has a thermostat in it that will make it run at a predetermined temp regardless of what you are using for coolant, if it gets too far out of that range it will log a 123 ECT code and pull on the check engine light. But if it sells more high dollar coolant changes then I am all for it, yeah right!
I can't remember the last time Volvo ran an actual radiator cap. Maybe on their 140/160 series but it has been sooooo long since I have owned/serviced any of those cars I don't really recall. Your coolant reservoir bottle is where you will do all of the filling and pressure testing on the 850. It has two coolant petcocks, one is in the lower left corner of the radiator and the other is located on the backside of the block on the right lower corner. Servicing the coolant on these cars is more of a drain and refill than it is a proper flush, but that is the way it is done, even on the older red engine cars. Just go ahead and drain the block and then drain any residual that is left in the bottom of the radiator, fill it back up with your coolant of choice, pressure test and get any air pockets out of it and you should be good to go.

Mark