Cadillac Repair: 99 Deville overheating, head bolts, engine coolant

Question
I have a 99 Deville it just started overheating did a pressure test on the system 12hr period with no leak down. after replacing Radiator and a water line replaced thermostat which I tested before installing the only place I'm loosing water is through the overflow so I then did a block test for co2 none in the cooling system cleared the purge line now I'm stomped why is it still overheating?

Answer
Because the lousy engine that you have was manufactured with steel head bolts going into an aluminum engine block that has aluminum threads and over time the steel head bolts start to rip the threads out of the engine block.

What you want to do is use a compression gage hose and attach constant air pressure to it and put air pressure 100 lbs into each spark plug hole and watch the air bubbles and or the explosion of engine coolant come out of the radiator cap opening.

To fix this you will have to driil out the bolt holes in the engine block and install steel heli-coils and larger diameter NEW head bolts.

This is a very very common problem.