Slant 6 Turbo 68Dart Project

if you were to run a hose from the top of the radiator to say a water bottle half full with the hose going under the water level and start it up cold and see bubbles i think that would work for letting you know weather or not exhaust gasses are getting in your cooling system. one or two bubbles would be understandable given the coolants rate of expansion when heated. if it bubbles persist constantly then you are beat and have to take it all apart.