Engine Overheating Issues

I got a 2000 Cadillac Deville thought it was ahead gasket its not. I took off the upper hose to the thermostat and I cranked it up and a little bit came out so one of my friends told me that I got air in the engine I'm going to do that today but something told me to take off the thermostat main pipeline and it's rusted out
Should I just give up on this engine or replace the lines
Need your help ASAP!
Should I just give up on this engine or replace the lines
Need your help ASAP!
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