Hi ive recently bought a 200tdi 90 (genuine def not disco) it keeps overheating. Temp gauge goes to red very very quickly but if I change gradient I.e down hill it seems to go back down. I haven't driven t far due to worrying about overheating. Both top and bottom hoses from the rad are warm/hot so waters circulating and the heaters working on hot so I presume thermostat is ok? The header tank is cold at all times. It has had a new rad fitted. Any ideas? I'm going to flush coolant tomorrow. I've read about dodgy Earth on the temp gauge, how would I know? Any ideas appreciated thanks