Its all new to me. I've always used straight water, because where I live by the sea, it doesn't snow, and in Winter, while puddles will freeze on the coldest Winter days, older cars were OK. When I rebuilt my Hudson, its six has an aluminum head, and a buddy filled my cooling system with what he said was the best you could get. Its blue, and that's all I know about it. He's a digger and heavy machine salesman, so I filled system, and run it for nearly 3 years. So, how often should I change it, and does it matter if I topped it up with a different brand? Any other relevant things I should know? My English 4x4 has an alloy V8 that also uses it, so I guess I'm stuck with having to use the stuff.