Temperature Gauge Problem on a 166 V6

[magic torch]

My Dad's got a 3.0 V6 166, with a temperature problem, hope someone can help.

The temperature gauge pretty much always stayed on 90, now it seems to run a bit hotter. When cruising on a motorway the gauge suddenly flicks up to red, stays there for a while, and the will suddenly drop back down. It's not using any water.

Any ideas, could it be the sensor???

[exgtt]

Suddenly dropping on the motorway usually indicates a thermostat issue, but it shouldnt zoom to the red. Maybe check thermostat/temp gague sender.

[magic torch]

Thanks, does anyone know where this is on a 166?