I don't have your type of engine, but....... Does the oil temp gauge spend any time at its "normal" reading before rising? What does the coolant temp say? If the gauge is anywhere near linear, you're getting the trigger at somewhere near 230-240. If the oil's that hot, the coolant ought to be warm also. Does the oil pressure drop at all as the oil temp supposedly rises? Oil temp ought to be a fairly straightforward system; sounds like either the sensor or the gauge is getting hinky. If all other indications are normal, I'd bet on the sensor.
John and Diane (RIP Lincoln, 21 FEB 22) RVM103 NHSO
Fulltimers since June, 2012
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element