I have already replaced the temp sensor, thermostat, and water pump. I flushed the coolant system, used my garden hose to drain the heater core, and checked the oil cap for white film, as well as the oil pan for signs of a head gasket issue. I'm now thinking that it's either the radiator or the head gasket. Both fans on the radiator are spinning as they should. Made sure to remove the air from the coolant system by pulsing the rad hoses until there were no bubbles in the coolant resoviur. My fuel gauge is a bit inconsistent; I’m not sure if that relates to the head gasket due to pressure. It also smells like something is... not burning but hot, which could just be due to overheating. I can smell it as soon as I start it up, and it's not coolant, since I only have water in the system. It's probably unrelated and just because it’s been sitting for a while...

So with all of that being answered, how can I test whether it's the rad or the head gasket so I know which step to take.

 

The first part of your title makes me think that your heater core is plugged, or that a valve to the heater core is not opening when it should to allow flow through the core. I'm not sure if it is part of the normal coolant circulation circuit before the thermostat opens but I would think it would be. Do you have good hot heat?

 

I have already replaced the temp sensor, thermostat, and water pump.

Did you pressure check the system? Tell us how it started when it overheated.

 

Take it away, Gary.