Just recently my XE Astra has been running really cold, just into the blue on the temprature guage, I thought it was the guage as it was fine one day and low the next. Anyways whilst sat in traffic at PVS the guage came to life and the fan was kicking in. So today I changed the thermostat, gave it a really good flush out and put in some good quality coldstream gold coolant. It now runs ok temprature wise. Only thing is before the temp would be exactly in the middle of the guage rising to 3/4 when hot and then the fan would kick in. Now it runs not quite at half way and the fan kicks in when the temp guage shows halfway in between red and blue (before it would be at least 3/4 up the guage). Also there's no release of pressure when I remove the expansion bottle cap even when its hot. There's no leaks that I can find. Am I just been over cautious or does this sound normal? Is this signs of a water pump on it's way out? Confused!