I said it before, your car has a blown head gasket. It overheated with no thermostat. If I were you the next thing to buy would be a hydrocarbons test kit.
Catalytic convertors hide the fact that the engine is burning coolant until they get really bad. From my experience with these engines, oil and coolant never mix, even in the case of severely blown gaskets. Here's a free way to tell. Have the engine completely cold. Remove the coolant crossover cap and fill with coolant to the top. Leave the crossover cap off and start the engine. If it shoots coolant out like a fountain then you have a blown head gasket.There is no other explanation on a cold engine, except combustion pressure in cooling system. These head gaskets typically fail between the #7 and#8 cylinders, but of course it could be anywhere.