yeah binky I have noticed the same thing with my car it the car idles a lot smoother & also the car runs a lot cooler then with the clutch fan I am running a inline switch in a 38mm diameter pipe thats 2" long in the top hose & it works a treat had to many probs with the copper prob leaking out around the top rad hose & didn't want to try & nip it up more as the RB 's run plastic tank's & was worryed about busting the tank outlet.
ALSO Ryosuke if u do go with a thermo fan KEEP THE FAN SHROUD on the rad just cut it a little so the thermo fan will fit on under it, it means that the fan will pull air through better, by the way sorry about my 1st post I though u had a line