Cadillac Northstar Overheats

This can be caused by a number of things most commonly failed headgaskets. You can use a cooling system pressure tester to pressurize the cooling system to see if it holds pressure if not then the headgaskets are likely leaking. You can also get a chemical tester to check for exahust gas in the coolant, if exhaust gas is present then replace the headgaskts. If both tests turn out fine first make sure your cooling fans are working if so remove your thermostat to see if engine stays cool, if so replace thermostat. If nothing works up to this point you may have a broken water pump or clogged radiator. You can use a laser temperature gun to check for hot/cold spots on the radiator if you find any replace. Otherwise remove the water pump to make sure the plastic impeller is not boke and still attatched to the shaft.