Ford fiesta 1.4 zetec. After 2-5 miles temp guage moves from normal to the red. Put heater on full blast and it comes back down. Alternatively drive steady, top gear 2000 rpm and guage comes down. Radiator fan comes on as it should. All movements of guage are quite rapid i.e/5 to 10 seconds for half guage needle movement. When stopped with needle in/near red no hubble bubble froth steam, so not obviously overheating. Car has had new thermostat, water pump, temp sender and the rad has been flushed.

Can anyone think of a possible cause, cure etc? It's tempting to say "oh it's only an electrical glitch" but sister-in-law doesn't want to blow the engine up.

possibly a voltage regulator problem?

Does that Rad feel HOT to touch?

If not then its got to be somehting to do with the clock cluster or wiring to it.

Sounds like it is air locked