We have been having engine high temp problems with our Komatsu D51EX-22. It has a rear mounted radiator with a self reversing fan to purge out dirt and debree. Lately the fan has been surging, or speeding up and slowing down, periodically. When this happens the engine temp gradually builds up to around 200 degrees. If the engine RPM is reduced, and the heater is run, the temp will drop off some. The weather has been cool or mild. Temps from 40 to 70 degree F.
The radiator most likely needs to be washed out as well as remove the belly pans and hood and give it a good cleaning. I just did my 39 this weekend and the engine temp is running a notch cooler on the gauge. This would be good maintenance as well as check the temp regulator and coolant. Our temps are similar to your area.
Mud Lugers did you find the problem? I’m having the same problem took it to the dealer. They told me the hydraulic pump was weak so they changed it charge me $15,000 and I still have the same problem anytime we operate the blade functions the fan slows down