I just replaced the heater core, I filled the core up through the heater core lines. I then burped the system. The thermostat is working properly and the radiator has been flushed multiple times with no visible rust.
This was a problem with the old heater core but I chalked that up to a rodent building a nest on top of the heater core. It may not have been the entire problem.
My question is, if I accidentally swapped the lines going and coming from the heater core, would this cause the heater core not to get warm.
If it's not that. I guess, I must have a vapor lock?