Took her for another run yesterday, a nice 80 mile round trip, about an hour each way, which is just about right. Looked this morning and once again the coolant was down by about 400ml. Although I can easily live with this I decided I should at least make an effort to track it down. So I covered the area under the car with newspapers, ran her up to temperature and then left her till she had been running for 20 mins. Result later.
then goes to about the 11:30 position at 95°C when I was pleased to see that my fan kicked in at exactly the right temperature (I have to use clock position as my NORMAL marking has rubbed off). The fan brought the temperature down to 90°C when the fan stopped. I then let it run through a couple of cycles as a final check. The screenshot of my program below shows the results.