What do you check next on a 95 dodge neon which over heated again after changing the thermostat and radiator cap heater core not leaking?

severe overheating may cause a blow out of the head gasket. Does the radiator build up excessive pressure quickly? can you see bubbles in the coolant? any white vapor or smoke from the exhaust? These are signs of a hole in the head gasket but you may have none or all of them. Check for water pump operation by looking for circulation in the radiator with the cap off, the water should swirl or at least move around. If it is still you may just need a water pump but at the same time look for those bubbles that I mentioned earlier that is a sign od exhaust gas entering the coolant system and will quickly force all the coolant out of the radiator through excess pressure. I was able to limp my Rodeo along for a week by using an old radiator cap and tearing out a small section of the gasket so that the pressure could escape without driving out all my coolant till I was able to tear down the engine.