Q: overheating on 2000 Volkswagen Jetta

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Changed radiator and fan motor. Now when I have the expansion tank cap off of the car or loose, the temp will stay at 190 degrees. When i put the cap back on tight the temp jumps to the red. I also have a new cap. I have flushed the cooling system with water and replaced the thermostat as well. Also, I have replaced about all of the little plastic pieces along the way. It doesnt seem to be leaking just overheating. The lower radiator hose or one of the heater core hoses really never gets hot like the others. keep in mind when i flushed i took every hose off one by one and water seemed to flow though all of them fine. Then through the entire system as well. Any bright ideas?
(1) Answer
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Possibly a Water Pump impeller that is worn and not circulating the water. When you changed your Thermostat, did you follow the correct Cooling system decavitation procedures? VWs are notorious for getting are air bubbles that prevent the coolant from circulating properly, especially after ANY cooling system work. I have SEEN engines over heat and melt the head on VWs all because of an Air Bubble after a Thermostat replacement. Good Luck!