As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CRUISE FLIGHT LEFT ENGINE OIL TEMPERATURE CLIMBED TO RED LINE REDUCTION IN POWER DID NOT PREVENT POWER FROM INCREASING TO APPROXIMATELY 120 DEGREES C. POWER WAS REDUCED FURTHER AND IN DESCENT THE OIL TEMP RETURNED TO NORMAL RANGE. WHEN POWER WAS INCREASE IN LEVEL OFF THE OIL TEMP BEGAN TO CLIMB AGAIN. LANDED AT DIVERSIONARY AIRPORT. OIL PRESSURE REMAINED IN NORMAL RANGE AT ALL TIMES. REPLACED OIL COOLER THERMOSTATIC VALVE AND PERFORMED HIGH OIL TEMP INSPECTION.