Q: Oily thick coolant

Hi there. This is a sure sign of a blown head gasket. This can happen when the car overheats causing the cylinder head gasket to fail. When this happens, this will allow oil to leak into the engine coolant passages as well as water to leak into the engine combustion chamber. You may also notice the exhaust smoking white as well as white smoke coming from under the hood when this happens. This can and eventually will (if not taken care of soon) cause major engine damage and ultimately the engine will fail due to loss of cylinder compression and many other related issues. I recommend having a certified professional, like one from YourMechanic, diagnose the overheating problem and proceed with the proper repairs.