Check if your loosing coolant or not. Although if it only gets to 3/4 chances are your not.
If you are, radiator pipes, water pump, cracked radiator etc
If your not, fans, thermostat, blocked radiator etc
So after a drive, park up and let it idle. Do the fans kick in as it goes past half?
Take the thermostat out and put it in some boiling water, does it open?
If the above are ok, get it pressure tested (I'd suspect a blocked radiator in this case, but other parts could be blocked too)
The temp on my vy ss doesn't move at all, traffic or open road. Always sits at 1/3