2002 PT cruiser running hot after all repairs have been done

My PT cruiser has turned into a hot mess!
After my local mechanic, who I think is competent, ran all the diagnostics,
change the radiator,  fan  assembly, thermostat,three radiator caps And heat
sensor valve above the thermostat, at a cost of around $600.
  Alas,  it is still running hot and blowing out the coolant very quickly?
It seems as if the cooling system is under extreme pressure
The water pump does not seem to be making any noise and seems to be
working properly
When I shut it off it sounds as if it has a demon growling at me from under the
hood
My mechanic finally said he could not fix it I would have to take it elsewhere
  That it probably was a engine seal that would have to be changed for about
$3000
  The car is less than $3000 and I am considering ordering a engine and
exchange it instead of putting in all the labor
Any suggestions how I can exercise this demon from my engine
  It is a low mileage car with only 65,000 miles on it? Any suggestions?
Thanks for your help