HARRY - A tool or gauge in a toolbox in the shop is worthless. Of anyone here I would think DATA to make CC's & Kohler engines last longer would mean something to you!
With a hydro, and increase of head or oil temp is corrected by just a slight movement of the hydro lever to slow tractor speed. Gears drives are slightly less easy.
I've never run a turbo diesel anything with a working pyro like Dave R. but thats why I want duplication of temps measured, EGT is an instant change, head temp a few seconds longer, oil temp comes up in a minute.
Once you know whats "normal" You can tell when things are "Not Normal". Data, Information.... It's why things last so much longer now. Typical tractor engine life used to be 2000-4000 hours. Now it's 6000-12000 hours. Oils better, filters are better, and the engines themselves are much better