Thank you to everyone who patiently answered my temperature regulation
questions!

I am replacing the following:
Expansion tank pressure cap (fairly sure its faulty)
Thermostat (definitely faulty)
Radiator fan switch (can't be sure its faulty but its cheaper than an
engine - when should it switch on?)

I am not replacing the temperature sensor (it seems to show a full range).

One remaining question is how do you test the coolant level warning sensor
in the expansion tank (the LED flashes OK on start-up)?

Lionel Tun
84 Caravelle GL, 183k miles
lionel@ark.prestel.co.uk