Temp gauge quickly goes into red when accelerating and drops back quickly when you take foot off accelerator. OK when idling. Instrument Cluster test shows no faults. Temp when gauge midway is 104C and when it moves into the red it shows 124C. After that if you don't ease off, the yellow exclamation light comes on and the engine goes into failsafe mode. No sign of overheating when bonnet up. Fan comes on at 100C. Thermostat and sensor changed and radiator flushed through and new 50/50 antifreeze put in. Any further thoughts would be appreciated???