I have a 2000 S70 that I just bought used with 99k. The antifreeze looks like its in good condition but I have no maintenance records so I am planning drain and fill. The fluid appears dark green not at all like Prestone bright green, I have never seen any this dark. I read that the Volvo fluid is blue-green, which could describe the fluid in my Volvo, but I am not sure. I plan to use the Zerex G-05 coolant when I refill the system. How concerned should I be about draining all of the fluid out. I usually just drain the radiator and not the engine block. Does the S-70 have a block drain and where is it? I change my fluid once a year, so I usally skip the block drain.

Should I flush the daylights out of the system to get as much of the old stuff out since I am switching types of fluid? Am I too concerned about mixing the fluids?

Thanks!