KA24DE Overheating and oil missing questions

[Fuego]

As far as your overheating goes, sounds like you have a giant air bubble in your coolant. I'd recommend burping it again. You may have warped the head, but there would be other symptoms with that. Attempt the fix then re-evaluate what problems still exist.

I wouldn't worry about belt slip from a car wash unless your belt is absolute shit or covered in grease.

Take your car to autozone and ask for them to pull the code.

For the oil, the stuff doesn't magically disappear. Pull your plugs and check for oil, then get back under the car with a bright ass light and give it another look.