Cadillac Repair: Cadillac Deville 1997 overheating, bolt holes, head bolts

Question
I have a 1997 Cadillac Deville that overheats and the temperature gauge goes up to 260 when I am driving.  The fluids is always overboiling and coming out of the expansion tank.  I took the vehicle to a mechanic and he change the thermostat and the the water pump, but the car still overheats.

Answer
Welcome to the well known cause of overheating for this engine which is caused by leaking head gaskets due to the steel head bolts stretching the aluminum head bolt holes in the engine block.

This IS very common and requires an engine rebuild and replacement of the head bolts and installing heli-coils in the engine block.