HI can a Cadillac converter issue case my radiator to blow?

Hello! A bad catalytic converter can make a car overheat by causing a backup of pressure in the cylinder head. If the Elantra is overheating, I would have her towed to a reputable mechanic and have them replace the Catalytic converter, and do a full fluid flush/change (engine oil, and radiator/cooling system). I hope this helps, and best of luck!

I also just looked at your photo. All that brown fluid, is your engine oil and your antifreeze (or coolant) mixed together. This is KEY INDICATOR of a blown head gasket. Do not drive the car as doing so will severely damage the engine if it hasn't already. I would have the car towed to the nearest reputable mechanic as soon as possible. Again, I would not recommend driving the vehicle. It could irreparably damage the engine.

WOW, your car threw up !