My main temp gauge has been raising and dropping recently, and I think I'm just being over caring.
It happends every now and again, and only when I'm at a stand still.
I've had the expansion tank top off to make sure no air in there...
Any ideas?....

 

How high up the gauge is it going? Mine used to do that in traffic, was a big airlock somewhere, and the header tank was full of water too. Have you refilled the system lately, had a pipe off or anything?