Using my 2003 plus8 daily, often in London traffic after a long haul up the M4, I concur with MOG16 and others. My temp gauge often reads 110C in traffic. If your cooling fan comes on and is blowing the right way, well and good. Mine goes off when temp shows 95 ish. Sometimes it'll cycle on and off frequently, which I consider normal. For peace of mind, I too fitted a bypass switch, which will keep temperature at about 95 (guage) in prolonged stop-start traffic, but the noise is distracting!
Regards, Phil
