Yellow and coagulated maybe? That is a sign that you have oil/a/f or G12 intermix. That is usually caused by the oil cooler. I would strongly suggest that you buy a new oil cooler and gasket (o-ring), and replace it and your oil/filter. Then Drain your cooling system fill with water with a 1/2 bottle of SHOUT laundry cleaner and water, you will be draining your coolant first, run in the car for about 15 minutes, then Drain and Flush and back flush again. Then drain and fill with the proper G12.