BE-300 Captain reported oil uncontrollable temperature on the left engine during cruise. The flight crew descended and slowed the aircraft; allowing time for oil temperature to decrease and continue to destination airport.

Narrative

During cruise flight at 26;000 feet; I noticed the L/H oil temperature in the yellow range at 100 degrees. I pointed out the discrepancy to the other crew member and continue to monitor while investigating the cause of the high oil temperature. The R/H oil temperature appeared normal at 49 degrees C. I noticed the outside air temperature was -38 degrees C. and then I remembered that experience at a previous company. The previous company that I worked; operated King Airs that were built for the military. The oil coolers on these aircraft were built larger than normal to compensate for operating in the high temperatures of the tropics. After the military sold his aircraft for surplus; the company that I used to work for bought them and operated them all over the world to include north of the Arctic Circle. The issues we would run into with using these large oil coolers was the oil would become super cool in the oil cooler and congealed. The congealed oil then blocked the oil cooler causing the engine oil to bypass the cooler and not cool the oil.This would appear as an increase in oil temperature do the oil cooler being blocked by congealing oil even though the outside air temperature was extremely low. Using his past experience The crew elected to reduced power to reduce the ram air over the oil cooler; and requested ATC to descend to FL220. By the time I took the corrective action the L/H oil temperature indicated 104 degrees C. Upon reducing the power to reduce ram airflow over the oil cooler I noticed the oil temperature climbing ceased and even decrease to 103 degrees C. After short delay; ATC granted a request to descend to FL220. Upon reaching 220 the left-hand oil temperature started to reduce rapidly below the caution range of 99 degrees C. Within a few minutes the oil temperature in the L/H engine return to a normal 70 degrees C. I do not believe that the oil temperature was within the caution range for longer than 10 minutes. In the future I will more closely monitor outside air temperature and closely monitor oil temperature is when the outside air temperature is above -35 degrees C.