Temp Gauge and Overheat Warning light

From: Mke
email: mike@secret-scotland.com
Date: 24 Apr 2006
Time: 09:07

Message

Over the last 2 weeks I've noticed my temperature gauge suddenly leaping from a safe temperature to 210F (~90C +) and at the same time the Overheating Warning light is coming on. However, it all appears to be a false warning. The Radiator Fan is not cutting in, but the Fan is OK. I am assuming that it is not a fault in the Thermo-switch as the expansion tank is not under pressure and the engine is not boiling over. What I do not understand is why a malfunction in the overheating sensor would also trigger a sudden rise in the temperature gauge. Thinking that the problem was a sticking thermostat, I removed the in line thermostat from the radiator top pipe and ran the car without a thermostat. After 20 mins driving at 30-40mph the temp gauge was still at zero, but then it suddenly from 0 F the Overheat Warning Light came on and the gauge leapt to 190F. Has anyone seen a similar fault? This is a series 2 2500ie Coupe.