I've got a 1999 Dodge Neon (181 000km), and I'm having some heating issues that are yet to be diagnosed. The car is in excellent shape, no serious issues. No problems with the head or head gaskets.
I had to replace the small radiator that was originally installed in the car from the factory due to overheading problems during hotter weather, this solved the problem.
Well now I've gone through 2 thermostats and I'm having them fail in the open position, during the winter. So I have no heat in the car, the rad and engine both warm up, but you can leave your hand on them after 45 minutes of running time.