Yep you're right, of course it does something, blocking it off worked as a quick fix to do what I had to do (hospital) then find someone to fix it.
Mazda wanted around 230 quid for a whole new radiator which isn't too bad really, however I got someone to replace the whole plastic top of the rad, flush it through, pressure test it, new coolant for 350 Riyals=75 quid, so not bad at all, especially as it was about 3 hrs work