I want to put some coolant in the overflow tank on a 2007 Subaru Outback. I look around for what coolant is OK to use, and find Pentofrost A2 can be used for this car make and year, according to their website. Then I see on the container it says not to use with other coolants. The coolant in the radiator is "green" in color, but I don't know what it is. Would you use this stuff to "top up?" If not, what coolant? I'm inclined to just use it, of course at 50/50 but want to hear other views. Thank you very much.