My Ferguson 5-8B Compactor/Roller has two temp gauges... Water Temp and Hydraulic Temp. They are essentially identical gauges... the type which can be bought at HF in a 3-gauge cluster...or any other Stewart-Warner type temp gauge. I’ve noticed on normal operations the Hyd Temp runs slightly cooler than engine Water Temp... typically Water temp runs 170-F and Hyd Temp runs 160-F.Don't forget your tractor's temperature gauge is also a great indicator of whether the tractor is being under/over worked. Unless you see the indicator climbing well above midrange you most likely aren't overworking the tractor.
This has become my habit... that of glancing occasionally at both temps and confirming that relationship of Hyd Temp not higher than Water Temp.
It’d be nice if HST Kubotas had a Hyd Temp gauge...and I suspect it would not be a difficult installation to Make.