When it gets to 90 it should sit there,
This time of the year diesels take a good time to warm up especially the 3.0 V6 it's a big lump of metal to get hot.
Drove to work last night 9 miles and it wasn't quite on 90 by the time I got to work.It was about 4 degrees outside.
The route is mainly 30-40 mph semi urban so engine not working too hard.
I was a little concerned by the time it took to warm up when I had the car so changed the thermostat but there was nothing wrong with the old one.and it made no difference to the warm up time of the car.
No good looking at what petrols do they put out a lot more waste heat than a diesel, thats why diesels are more efficient.
Karl.