I fitted a Radtec after 3 CC Rad failures on my Sigma. The Radtec is a super looking product; I didnt know whether to put it on the mantelpiece or fit it! And after much 'undecided hovering' at the Halfords shelves opted for Halfords Blue NAP coolant, intent on changing it yearly. I decided on non OAT as I was also told by Radtec that they can/will rework a failed Radtec rad if an OAT coolant is not used. The engine runs a tad hotter, which is not a bad thing, and so far so good. But if anyone tells me Blue NAP is not the thing I could change it!!