SA-227 Captain reported operating with the left engine at idle power for the last portion of the flight because of high oil temperature.

Narrative

Nearing the end of cruise; the left engine was operating a little warm and was about 100 degrees C. While that was within limitations; I was keeping my eye on it to make sure it didn't go higher. ATC gave me a descent to 4000 ft. so I reduced power and started down figuring that would help the temps drop. In the descent I had the engines at 40-45% torque and was at roughly 230 kts. Unfortunately the temperature did not drop and actually started to climb into the yellow. I proceeded to run QRH yellow tab 6 'high oil temperature; during flight'. At the same time Center gave me 'slowest practical speed' so with both engines at idle and still descending I again hoped the oil temperature would drop. Fortunately the oil temperature did drop while at flight idle in the descent back into the yellow so I elected not to do the preplanned engine shutdown at that time and attempt a landing since I was about to turn final. Leveling off at 4000 ft. and bringing power back in to maintain altitude the oil temperature started to climb again so I pulled the engine back to idle and let Center know that I was making straight in for the runway. I gave them my souls on board and fuel and continued the rest of my visual landing with the left engine at idle and sitting in the yellow for the oil temperature. Once I reached the ground and the engine continued to idle on the taxi in the oil temperature came back into the top of the green for taxi in and shutdown. Airplane written up for LH engine oil temperature exceeding limitations.Initially I thought that maybe there was some foreign contamination over the oil cooler but upon landing I inspected the oil cooler inlet and found no contamination. Maintenance believes the oil is over serviced in the left engine; however when I look in the sight glass it appears to be normal.