I have exactly the opposite problem to Yendall24.
Driving home from work on Friday, I'd got about 2 thirds of my way home, off the dual carriageway and back onto country roads when suddenly my Coolant warning shouted at me.
Sure enough the temperature gauge was way up to about 110deg. I looked under the bonnet and the header tank was extremely hot. Carefully I released the pressure (and steam) from the bottle (which I know I shouldn't have done...) and let the temperature drop a bit.
After 5 mins or so I restarted the car, which had dropped to about 95. I was about 5 mins from home so I figured I could nurse it home.
But after about 2 mins the warning came up again. Again I pulled over and did the same as before. The journey home took me an extra 25 minutes because of the stopping and starting.
Today I decided to investigate, so I drained the coolant and changed the thermostat (I was hoping for a quick fix). Refilled coolant and thought I'd suck it and see. I Started the car, after about 10 mins idling it settled at the usual 90deg, where it stayed for about 5 minutes. Then it started to rise, and settled at about 100. I then thought i'd give it a quick spin as idling in a garage isn't a fair trial.
However, by the time I was 200yds down the road the warning was back on.
Car is back in the garage. Coolant level is about a quarter past minimum with no obvious loss. Header tank is very hot. Water pipe into rad is very hot, water pipe out seems to be cold. Thermostat is new (previous one worked fine when tested in a saucepan)
I'm pretty much resigned to thinking its the water pump.
Your thoughts would be much appreciated!
