Now I've got the zetec all set up I have been out racking up some miles and smiles.

However, I have a strange temperature issue. I have just tested it driving back from a friends house which was mostly motorway driving. Got on the motorway about 4-5 minutes after leaving his and sat the car at 70mph
For the first bit of my motorway drive the temp gauge would go back and fourth from point 1 to point 2 only stopping at each point for a few seconds. (excuse the crummy drawing)


After about 15-20 minutes of driving the needle then dropped to around point 1, about midway on the gauge, and stayed there for the remainder of the drive even when applying a bit of boost and driving through slower speed limits and traffic light stops.
(I know these gauges are old and not the best but the change is so quick and drastic on the scale of the guage its hard not to notice)
I know the Cold start for the ecu has not been fine tuned yet and the car can be a touch lumpy on start up, also I'm using the CVH thermostat housing with a brand new standard thermostat.

So and ideas what this could be?
Thanks.