2006 XC70- I want to clean out the cooling system. I am sure it has the original anti-freeze. Do I just open the valve at the bottom of the radiator? Or is this not enough? I do not know the brand of anti -freeze in the car now, so I think I have to be careful to not mix brands...or do I? So, how do I clear out all the old? Or does it matter if some is left in, and the new brand does not match?

As you have discovered, nobody changes the antifreeze. Draining the radiator and refilling is better than whatever is in there. Like Klaus says drain the radiator and the block and you will be good. Look for a universal or compatible with everything antifreeze. Using distilled water ( fewer minerals) for the 50/50 mix is not a bad idea.

Greg

There are 2 drains, one on the radiator and one on the engine block. Even after draining, there will be a pint or so in the heater core. If you are really fastidious about it, drain the system, add 2 gallons of distilled water, run the engine for a few minutes, drain everything again, then fill with antifreeze and distilled water.

--
Keeping it running is better than buying new