My XJR cooling fans are temporarily out of action, which doesn't matter - if I am moving, it sits rock steady at 86'C
I am getting a new radiator fitted next week anyway, as preventative maintenance before the 22 year old plastic tanks fail and I potentially warp the head, so the dodgy fans can be fixed at the same time.

So today i fitted my Kiwi3 OBDII device.
the needle starts to rise off "C" at about 56'C and climbs quickly to the lefthand edge of "N" by about 66'C. So it is then another 20'C temp rise until normal hot running temp is reached (86'C) which explains why it takes so long for the heater to kick in when you think the car is up to temp, but actually isn't (between 66 and 86 degrees).
It then doesn't budge off lower edge of "N" until about 96'C, but then rises quickly. It gets to the right-hand edge of "N" by 97-98'C then jumps up to the next notch by 99'C
I then chicken out and turn the car off. (I have hit the upper limits in my driveway, as the last 3/4 mile home involves about 120m climb.)

 

Good information, thank you.