The impossible to solve overheating problem

Just back from the garage, I had the original radiator installed and we put a Co2 meter at the opening to the radiator, no sign of Co2 at all. The guy was nice and didn't charge me for the 15 minutes.
I also did BigBlockMopars test before this smelled for exhaust, could not smell anything either. So I think it's safe to say my theory of combustion in the coolant is gone. The guy at the garage said that if I'm losing coolant into the cylinders it's would be very obvious ammounts of white smoke and that the engine might run bad on cold start up.
Going to start trying everything that has been suggested later on today.