I'll second Ron's post. Kubota's run cool on the guage until the screen gets clogged up. You notice it in the late summer and fall when cutting tall grass and weeds, the seed pods and stuff will clog the air intake holes and the screens. 5 min of R&R and the temp drops.
Also, Diesels run cooler than gas engines. That's one reason they are so good at constant high load applications.
Enjoy your tractor!
jb