I have an elderly Fiesta as my run about in the south of France - I'm sure mechanically it's pretty much the same as UK models.

This week I gave it a bit more of a challenge than its usual trips to airport/beach/supermarket by taking it up some long steep climbs on roads in the southern Alps. It performed fine but at one viewpoint stop I noticed a sizzling noise coming from the bonnet and on investigation the coolant was actually simmering and a bit of pressure released from the cap - though the coolant level hadn't noticeably dropped. I let it cool and continued, and on other steep climbs it happened again.

I noticed that at no point did the electric fan cut in, and I don't think I've ever seen the electronic temp gauge on the dashboard move from Normal.

In the end I cut short my mountain drive (not wanting to run the risk of it overheating on a moubtain pass) and headed gently back on the motorway, where the air through the radiator seemed to keep it sufficiently cool and I got back fine.

Would the fact that the temp gauge never moves from Normal and the fan doesn't cut in even when it's obviously very hot suggest that the thermostat is stuck? Presumably it could also be the fan that's failed or a fuse.

It may not be so critical for my usual short local trip's but obviously I don't want to risk it overheating or breaking down while on a trip, even locally.

Thanks for any thoughts you may have.