[deezee]

Right, The coolant header tank I have is utterly unsuitable as its overflow only and not pressurised! Can anyone recommend a simple (ideally square) coolant header tank that has a pressurised cap on it?

Also, does the header tank need an in and an out on it? Or can you just break into a rad hose with a Tee Piece and have it connected that way? The more I look into different manufacturers coolant systems, the more complex they seem.