Temperature guage troubles

[Prickly_buzz]

Hello,

Hoping someone can help, I've got a 1.8 2001 Focus.

The cars very low mileage at just 36k, its had new coolant bottle, cap and anti-freeze recently.

I was driving on the motorway yesterday and as I went up a hill or accelerated harder to overtake the temperature gauge rose from its normal mid-way 12 o'clock point to in the red! This took all of about 15 seconds and as soon as I came off the accelerator it took about the same amount of time for it to return to its normal position.
When I came off the motorway I sat in traffic for approx 15 mins and the gauge behaved itself perfectly. When I got home I checked the car, the coolant level was spot on, it didn't seem excessively hot, all the coolant pipes where getting hot, the heating works and the cooling fans cut in.
I don't actually think the car is getting as hot as the gauge would suggest as it wouldn't heat up and cool down again all within 30 seconds?!

any ideas?

[Matthen]

Mine goes the other way. Open the taps and it will crawl all the way back down to zero then re-rise. I've put it down to fords st electronics (the dashboards are a joke)(and maybe a broken thermostat).

Could have been an airlock mechanically.

[Prickly_buzz]

I have spent a little more time looking into this and have since discovered that the car is 'overheating' However from the centre normal point on the gauge to the red is only 20 degrees i.e. the centre is ~100 degrees and the red is ~120 degrees. this explains why it moves up and down so quickly.

I have changed the thermostat and flushed the cooling system and although this has improved the problem it is still there.

I'm starting to sway towards the water pump as I know these have plastic impellers which are prone to breaking. The only thing I was thinking is if it was the water pump wouldn't it cause a cooling problem all the time not just at 80mph or under load?