GMC YUKON OIL IN COOLANT

I Have Oil In The Antifreeze (thick Light Brown Liquid At The Top Of The Radiator) And My Check Engine Light Is On Giveing A P0161 - O2...

Two Years Ago, My Suv Was Overheating. I Had Paid A Mechanic (not My Regular Mechanic) To Replace The Radiator And Flush The System. After...