Thanks for the tips on bleeding!

Firstly though I 'cleaned out' the expansion tank pressure cap by rinsing,
tapping,
blowing and sucking on it. I think it had an effect because I did loosen up
the valves by blowing and sucking. Is it worth replacing the part, 13 years
old and new one only costs 8.81 UK pounds?

Since then the temperature fluctuations seem not so wild, just a gradual
build up to just under 50% on a long journey, and only up to about 25% on a
short journey.

About bleeding:
I drove the front of the car up a steep driveway and with the engine hot
and running I released the radiator bleed screw, and coolant immediately
came out.
Does this indicate the radiator is full of coolant? I mean is it important
to release the bleed screw near the engine and
open the expansion tank as per instructions, or is that only for severe
cases? The refill tank level rises slightly sometimes during driving and
comes back down to
normal when cool.

Lionel Tun
84 Caravelle GL, 183000 miles
lionel@ark.prestel.co.uk