After A/C Add On Engine Overheats Really Bad

Did the aftermarket A/C change any of the water pump pulley ratios?

There is now a condenser in front of your radiator that will impede some air flow. Even with the A/C off. Maybe that was just enough to get it hot.

Do you run the A/C water pump? IIRC, there is an A/C water pump and a non A/C pump.

There are some cruddy thermostats out there. The owner of Milodon during a plant tour told us that the Milodon thermostats that are built to his spec have two manufacturing plants: One in the U.S. and one in India. His contract specifies he will only buy thermostats made in the U.S.

I think it's a really good idea to invest in a $30 harbor freight inferred laser thermometer. That way you can tell what temperature of: t-stat housing, temp sensor, rad inlet hose, rad. outlet hose, various spots on your radiator. If you have certain areas of your radiator that are not consistent with other close areas, you have a blockage.

Also, many times temp sensor are incorrect. You can check that with a infrared gun. Like I think most new mopar temp sensors are wrong. Shannon at www.Redlinegaugeworks.com adds an resistor to get the correct resistance for the gauge to show correctly.